Title of Invention: PHOTOGRAPHING OPTICAL LENS ASSEMBLY, IMAGE CAPTURING UNIT AND ELECTRONIC DEVICE Abstract: A photographing optical lens assembly includes, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element and a seventh lens element. The first lens element with refractive power has an object-side surface being convex in a paraxial region thereof. Each second, third, fourth and fifth lens element has refractive power. The sixth lens element with negative refractive power has an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof, and both of the surfaces of the sixth lens element are aspheric. The seventh lens element with refractive power has an image-side surface being concave in a paraxial region thereof, wherein the image-side surface has at least one convex shape in an off-axis region thereof. Detailed Description: RELATED APPLICATIONS This application is a continuation patent application of U.S. application Ser. No. 15/147,679, filed on May 5, 2016, which is a continuation patent application of U.S. application Ser. No. 14/513,827, filed on Oct. 14, 2014, the entire contents of which are hereby incorporated by reference for which priority is claimed under 35 U.S.C. §120. The U.S. application Ser. No. 14/513,827, filed on Oct. 14, 2014, is a non-provisional application claims priority to Taiwan Application Serial Number 103126474, filed on Aug. 1, 2014, which is incorporated by reference herein in its entirety. BACKGROUND Technical Field The present disclosure relates to a photographing optical lens assembly, an image capturing unit and an electronic device, more particularly to a photographing optical lens assembly and an image capturing unit applicable to an electronic device. Description of Related Art In recent years, with the popularity of electronic devices having camera functionalities, the demand of miniaturized optical systems has been increasing. The sensor of a conventional optical system is typically a CCD (Charge-Coupled Device) or a CMOS (Complementary Metal-Oxide-Semiconductor) sensor. As the advanced semiconductor manufacturing technologies have allowed the pixel size of sensors to be reduced and compact optical systems have gradually evolved toward the field of higher megapixels, there is an increasing demand for compact optical systems featuring better image quality. Due to the popularity of electronic devices with high-end specifications, such as smart phones, tablet personal computers and wearable apparatus, the requirements for large aperture and large image sensor of present compact optical systems increase significantly whereby the number of the lens elements increases. Therefore, it is unfavorable for keeping the optical systems compact. Furthermore, the aberration is severe when the optical system includes a large aperture. Therefore, it is important to keep the optical system compact and improve the image quality at the same time when the optical system includes a large aperture and a large image sensor. SUMMARY According to one aspect of the present disclosure, a photographing optical lens assembly includes, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element and a seventh lens element. The first lens element with refractive power has an object-side surface being convex in a paraxial region thereof. The second lens element has refractive power. The third lens element has refractive power. The fourth lens element has refractive power. The fifth lens element has refractive power. The sixth lens element with negative refractive power has an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof, wherein both of the object-side surface and the image-side surface of the sixth lens element are aspheric. The seventh lens element with refractive power has an image-side surface being concave in a paraxial region thereof, wherein the image-side surface of the seventh lens element has at least one convex shape in an off-axis region thereof, and both of an object-side surface and the image-side surface of the seventh lens element are aspheric. The photographing optical lens assembly has a total of seven lens elements with refractive power. An air gap in a paraxial region is between any two of the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element, the sixth lens element and the seventh lens element that are adjacent to each other. When an axial distance between the object-side surface of the first lens element and an image surface is TL, a maximum image height of the photographing optical lens assembly is ImgH, and the following condition is satisfied: TL/ImgH<3.0. According to another aspect of the present disclosure, an image capturing unit includes the photographing optical lens assembly according to the aforementioned aspect and an image sensor, wherein the image sensor is disposed on the image side of the photographing optical lens assembly. According to still another aspect of the present disclosure, an electronic device includes the image capturing unit according to the aforementioned aspect. BRIEF DESCRIPTION OF THE DRAWINGS The disclosure can be more fully understood by reading the following detailed description of the embodiments, with reference made to the accompanying drawings as follows: FIG. 1 is a schematic view of an image capturing unit according to the 1st embodiment of the present disclosure; FIG. 2 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 1st embodiment; FIG. 3 is a schematic view of an image capturing unit according to the 2nd embodiment of the present disclosure; FIG. 4 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 2nd embodiment; FIG. 5 is a schematic view of an image capturing unit according to the 3rd embodiment of the present disclosure; FIG. 6 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 3rd embodiment; FIG. 7 is a schematic view of an image capturing unit according to the 4th embodiment of the present disclosure; FIG. 8 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 4th embodiment; FIG. 9 is a schematic view of an image capturing unit according to the 5th embodiment of the present disclosure; FIG. 10 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 5th embodiment; FIG. 11 is a schematic view of an image capturing unit according to the 6th embodiment of the present disclosure; FIG. 12 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 6th embodiment; FIG. 13 is a schematic view of an image capturing unit according to the 7th embodiment of the present disclosure; FIG. 14 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 7th embodiment; FIG. 15 a schematic view of an image capturing unit according to the 8th embodiment of the present disclosure; FIG. 16 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 8th embodiment; FIG. 17 a schematic view of an image capturing unit according to the 9th embodiment of the present disclosure; FIG. 18 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 9th embodiment; FIG. 19 a schematic view of an image capturing unit according to the 10th embodiment of the present disclosure; FIG. 20 shows spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 10th embodiment; FIG. 21 shows an electronic device according to an embodiment; FIG. 22 shows an electronic device according to another embodiment; and FIG. 23 shows an electronic device according to still another embodiment. DETAILED DESCRIPTION A photographing optical lens assembly includes, in order from an object side to an image side, a first lens element, a second lens element, a third lens element, a fourth lens element, a fifth lens element, a sixth lens element and a seventh lens element. The photographing optical lens assembly has a total of seven lens elements with refractive power. According to the photographing optical lens assembly of the present disclosure, an air gap in a paraxial region is arranged between any two of the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element, the sixth lens element, and the seventh lens element that are adjacent to each other, that is, each of the first through seventh lens elements of the photographing optical lens assembly is a single and non-cemented lens element. Moreover, the manufacturing process of the cemented lenses is more complex than the non-cemented lenses. In particular, an image-side surface of one lens element and an object-side surface of the following lens element need to have accurate curvature to ensure these two lens elements will be highly cemented. However, during the cementing process, those two lens elements might not be highly cemented due to displacement and it is thereby not favorable for the image quality of the photographing optical lens assembly. Therefore, there is an air gap in a paraxial region between any two of the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element, the sixth lens element, and the seventh lens element that are adjacent to each other in the present disclosure for improving the problem generated by the cemented lens elements. The first lens element with refractive power has an object-side surface being convex in a paraxial region thereof. Therefore, it is favorable for avoiding overloading the refractive power on one single lens element resulting in excessive aberrations. It is also favorable for reducing the sensitivity of the photographing optical lens assembly. The second lens element has refractive power. Therefore, it is favorable for adjusting the refractive power with the first lens element so as to correct the aberration from the first lens element. The third lens element has refractive power. Therefore, it is favorable for effectively reducing the sensitivity of the photographing optical lens assembly. Furthermore, it is favorable for balancing the arrangement of the refractive powers of the photographing optical lens assembly so as to correct the astigmatism and the distortion in the peripheral region of the image, thereby improving the image quality. The fourth lens element has refractive power. Therefore, it is favorable for adjusting the refractive power with the third lens element so as to balance the arrangement of the refractive powers of the photographing optical lens assembly. The fifth lens element with refractive power can have an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof. Therefore, it is favorable for correcting the astigmatism of the photographing optical lens assembly so as to improve the image quality. The sixth lens element with negative refractive power has an object-side surface being concave in a paraxial region thereof and an image-side surface being convex in a paraxial region thereof. The image-side surface of the sixth lens element can have at least one concave shape in an off-axis region thereof. Therefore, it is favorable for correcting the aberration of the photographing optical lens assembly with a large aperture. Therefore, it is favorable for evenly distributing the refractive powers of the photographing optical lens assembly close to an image surface so as to reduce the sensitivity of the photographing optical lens assembly. The seventh lens element with refractive power has an image-side surface being concave in a paraxial region thereof. The image-side surface of the seventh lens element has at least one convex shape in an off-axis region thereof. Both of an object-side surface and the image-side surface of the seventh lens element are aspheric. Therefore, it is favorable for the principal point of the photographing optical lens assembly being positioned away from the image side of the photographing optical lens assembly so as to reduce a total track length of the photographing optical lens assembly. It is also favorable for reducing a back focal length so as to keep a compact size thereof. When an axial distance between the object-side surface of the first lens element and the image surface is TL, a maximum image height of the photographing optical lens assembly (half of a diagonal length of an effective photosensitive area of an image sensor) is ImgH, the following condition is satisfied: TL/ImgH<3.0. Therefore, it is favorable for keeping the photographing optical lens assembly compact so as to be equipped in an electronic device. Preferably, the following condition is satisfied: TL/ImgH<2.2. When a focal length of the photographing optical lens assembly is f, a composite focal length of the first lens element and the second lens element is f12, the following condition is satisfied: 0.25<f/f12<1.5. Therefore, it is favorable for arranging the refractive powers of the first lens element and the second lens element so as to further correct the aberration of the photographing optical lens assembly. Furthermore, it is favorable for reducing the back focal length of the photographing optical lens assembly so as to keep a compact size thereof. When an Abbe number of the first lens element is V1, an Abbe number of the second lens element is V2, an Abbe number of the fifth lens element is V5, an Abbe number of the sixth lens element is V6, the following condition is satisfied: 1.5<(V1+V2)/(V5+V6)<3.0. Therefore, it is favorable for correcting the chromatic aberration of the photographing optical lens assembly. When a focal length of the sixth lens element is f6, the focal length of the photographing optical lens assembly is f, the following condition is satisfied: f6/f<−1.0. Therefore, it is favorable for properly adjusting the refractive power of the sixth lens element so as to reduce the back focal length of the photographing optical lens assembly, thereby keeping a compact size. When the focal length of the photographing optical lens assembly is f, the focal length of the sixth lens element is f6, a focal length of the seventh lens element is f7, the following condition is satisfied: −1.8<(f/f6)+(f/f7)<−0.5. Therefore, it is favorable for properly arranging the refractive powers of the sixth lens element and the seventh lens element so as to reduce the back focal length of the photographing optical lens assembly, thereby reducing the total track length thereof. When an axial distance between the image-side surface of the seventh lens element and the image surface is BF, the focal length of the photographing optical lens assembly is f, the following condition is satisfied: BF/f<0.35. Therefore, the back focal length of the photographing optical lens assembly is sufficient for disposing additional opto-mechanical components. When a maximum refractive index of one single lens element among the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element, the sixth lens element and the seventh lens element is Nmax, a minimum refractive index of one single lens element among the first lens element, the second lens element, the third lens element, the fourth lens element, the fifth lens element, the sixth lens element and the seventh lens element is Nmin, the following conditions are satisfied: 1.60<Nmax<1.70, and 1.50<Nmin<1.60. Therefore, it is favorable for preventing the refractive indices from becoming too small so as to correct the aberration of the photographing optical lens assembly. Meanwhile, it is also favorable for preventing the refractive indices from becoming too large so as to avoid excessively small Abbe numbers. When an axial distance between the object-side surface of the first lens element and the image-side surface of the seventh lens element is Td, an entrance pupil diameter of the photographing optical lens assembly is EPD, the following condition is satisfied: Td/EPD<3.0. Therefore, it is favorable for providing sufficient amount of incident light and keeping the photographing optical lens assembly compact. When the Abbe number of the sixth lens element is V6, the following condition is satisfied: 10<V6<32. Therefore, it is favorable for correcting the chromatic aberration of the photographing optical lens assembly. When the focal length of the photographing optical lens assembly is f, a curvature radius of the image-side surface of the seventh lens element is R14, the following condition is satisfied: 0.20<R14/f<0.60. Therefore, it is favorable for reducing the back focal length of the photographing optical lens assembly. When a central thickness of the sixth lens element is CT6, a central thickness of the seventh lens element is CT7, the following condition is satisfied: 0.75<CT6/CT7<1.33. Therefore, it is favorable for properly adjusting the thicknesses of the sixth lens element and the seventh lens element. Therefore, it is favorable for assembling the photographing optical lens assembly so as to increase the manufacturing yield rate. When a curvature radius of the image surface is Rimg, the following condition is satisfied: −500 [mm]<Rimg<−20 [mm]. Therefore, it is favorable for correcting the astigmatism in the peripheral region of the image so as to effectively improve the image quality of the off-axis. When an f-number of the photographing optical lens assembly is Fno, the following condition is satisfied: Fno<2.0. Therefore, it is favorable for obtaining large aperture so as to take sharp images under insufficient light conditions by fast shutter speed. When a sum of central thicknesses of the first lens element through the seventh lens element is ΣCT (that is, a sum of central thicknesses of the first, second, third, fourth, fifth, sixth, and seventh lens elements), the axial distance between the object-side surface of the first lens element and the image-side surface of the seventh lens element is Td, and the following condition is satisfied: 0.60<ΣCT/Td<0.85. Therefore, it is favorable for properly adjusting the axial distances and the thicknesses of the lens elements so as to effectively assemble and arrange the photographing optical lens assembly. According to the photographing optical lens assembly of the present disclosure, the photographing optical lens assembly can include at least one stop, such as an aperture stop, a glare stop or a field stop. Said glare stop or said field stop is set for eliminating the stray light and thereby improving the image quality thereof. According to the photographing optical lens assembly of the present disclosure, an aperture stop can be configured as a front stop or a middle stop. A front stop disposed between an imaged object and the first lens element can provide a longer distance between an exit pupil of the photographing optical lens assembly and the image surface and thereby improves the image-sensing efficiency of an image sensor. A middle stop disposed between the first lens element and the image surface is favorable for enlarging the field of view of the photographing optical lens assembly and thereby provides a wider field of view for the same. According to the photographing optical lens assembly of the present disclosure, the lens elements thereof can be made of glass or plastic material. When the lens elements are made of glass material, the distribution of the refractive power of the photographing optical lens assembly may be more flexible to design. When the lens elements are made of plastic material, the manufacturing cost can be effectively reduced. Furthermore, surfaces of each lens element can be arranged to be aspheric, since the aspheric surface of the lens element is easy to form a shape other than spherical surface so as to have more controllable variables for eliminating the aberration thereof, and to further decrease the required number of the lens elements. Therefore, the total track length of the photographing optical lens assembly can also be reduced. According to the photographing optical lens assembly of the present disclosure, each of an object-side surface and an image-side surface has a paraxial region and an off-axis region. The paraxial region refers to the region of the surface where light rays travel close to the optical axis, and the off-axis region refers to the region of the surface away from the paraxial region. Particularly, when the lens element has a convex surface, it indicates that the surface is convex in the paraxial region thereof; when the lens element has a concave surface, it indicates that the surface is concave in the paraxial region thereof. Moreover, when the region of refractive power or focus of a lens element is not defined, it indicates that the region of refractive power or focus of the lens element is in the paraxial region thereof. According to the photographing optical lens assembly of the present disclosure, an image surface of the photographing optical lens assembly, based on the corresponding image sensor, can be flat or curved, especially a curved surface being concave facing towards the object side of the photographing optical lens assembly. According to the present disclosure, an image capturing unit is provided. The image capturing unit includes the photographing optical lens assembly according to the aforementioned photographing optical lens assembly of the present disclosure, and an image sensor, wherein the image sensor is disposed on the image side of the aforementioned photographing optical lens assembly, that is, the image sensor can be disposed on or near an image surface of the aforementioned photographing optical lens assembly. In some embodiments, the image capturing unit can further include a barrel member, a holding member or a combination thereof. In FIG. 21, FIG. 22 and FIG. 23, an image capturing device 10 may be installed in, but not limited to, an electronic device, including a smart phone (FIG. 21), a tablet personal computer (FIG. 22) or a wearable device (FIG. 23). The three exemplary figures of different kinds of electronic device are only exemplary for showing the image capturing device of present disclosure installing in an electronic device and is not limited thereto. In some embodiments, the electronic device can further include, but not limited to, a display unit, a control unit, a storage unit, a random access memory unit (RAM), a read only memory unit (ROM) or a combination thereof. According to the photographing optical lens assembly of the present disclosure, the photographing optical lens assembly can be optionally applied to moving focus optical systems. Furthermore, the photographing optical lens assembly is featured with good capability in corrections and high image quality, and can be applied to 3D (three-dimensional) image capturing applications, in products such as digital cameras, mobile devices, digital tablets, wearable devices, smart televisions, wireless monitoring devices, motion sensing input devices, driving recorders, rear view cameras and other electronic imaging devices. According to the above description of the present disclosure, the following specific embodiments are provided for further explanation. 1st Embodiment FIG. 1 is a schematic view of an image capturing unit according to the 1st embodiment of the present disclosure. FIG. 2 shows, in order from left to right, spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 1st embodiment. In FIG. 1, the image capturing unit includes the photographing optical lens assembly (its reference numeral is omitted) of the present disclosure and an image sensor 195. The photographing optical lens assembly includes, in order from an object side to an image side, an aperture stop 100, a first lens element 110, a second lens element 120, a third lens element 130, a fourth lens element 140, a fifth lens element 150, a sixth lens element 160, a seventh lens element 170, an IR-cut filter 180 and an image surface 190, wherein the photographing optical lens assembly has a total of six lens elements (110-170) with refractive power. There is an air gap in a paraxial region between any two of the first lens element 110, the second lens element 120, the third lens element 130, the fourth lens element 140, the fifth lens element 150, the sixth lens element 160 and the seventh lens element 170 that are adjacent to each other. The first lens element 110 with positive refractive power has an object-side surface 111 being convex in a paraxial region thereof and an image-side surface 112 being concave in a paraxial region thereof. The first lens element 110 is made of plastic material and has the object-side surface 111 and the image-side surface 112 being both aspheric. The second lens element 120 with positive refractive power has an object-side surface 121 being convex in a paraxial region thereof and an image-side surface 122 being concave in a paraxial region thereof. The second lens element 120 is made of plastic material and has the object-side surface 121 and the image-side surface 122 being both aspheric. The third lens element 130 with negative refractive power has an object-side surface 131 being convex in a paraxial region thereof and an image-side surface 132 being concave in a paraxial region thereof. The third lens element 130 is made of plastic material and has the object-side surface 131 and the image-side surface 132 being both aspheric. The fourth lens element 140 with positive refractive power has an object-side surface 141 being planar in a paraxial region thereof and an image-side surface 142 being convex in a paraxial region thereof. The fourth lens element 140 is made of plastic material and has the object-side surface 141 and the image-side surface 142 being both aspheric. The fifth lens element 150 with negative refractive power has an object-side surface 151 being concave in a paraxial region thereof and an image-side surface 152 being convex in a paraxial region thereof. The fifth lens element 150 is made of plastic material and has the object-side surface 151 and the image-side surface 152 being both aspheric. The sixth lens element 160 with negative refractive power has an object-side surface 161 being concave in a paraxial region thereof and an image-side surface 162 being convex in a paraxial region thereof. The image-side surface 162 of the sixth lens element 160 has at least one concave shape in an off-axis region thereof. The sixth lens element 160 is made of plastic material and has the object-side surface 161 and the image-side surface 162 being both aspheric. The seventh lens element 170 with negative refractive power has an object-side surface 171 being convex in a paraxial region thereof and an image-side surface 172 being concave in a paraxial region thereof. The image-side surface 172 of the seventh lens element 170 has at least one convex shape in an off-axis region thereof. The sixth lens element 170 is made of plastic material and has the object-side surface 171 and the image-side surface 172 being both aspheric. The IR-cut filter 180 is made of glass and located between the seventh lens element 170 and the image surface 190, and will not affect the focal length of the photographing optical lens assembly. The image sensor 195 is disposed on or near the image surface 190 of the photographing optical lens assembly. The equation of the aspheric surface profiles of the aforementioned lens elements of the 1st embodiment is expressed as follows: X  ( Y ) = ( Y 2 / R ) / ( 1 + sqrt  ( 1 - ( 1 + k ) × ( Y / R ) 2 ) ) + ∑ i   ( Ai ) × ( Y i ) , where, X is the relative distance between a point on the aspheric surface spaced at a distance Y from an optical axis and the tangential plane at the aspheric surface vertex on the optical axis; Y is the vertical distance from the point on the aspheric surface to the optical axis; R is the curvature radius; k is the conic coefficient; and Ai is the i-th aspheric coefficient, and in the embodiments, i may be, but is not limited to, 4, 6, 8, 10, 12, 14 and 16. In the photographing optical lens assembly of the image capturing unit according to the 1st embodiment, when a focal length of the photographing optical lens assembly in the paraxial region thereof is f, an f-number of the photographing optical lens assembly is Fno, and half of a maximal field of view of the photographing optical lens assembly is HFOV, these parameters have the following values: f=5.30 mm; Fno=2.10; and HFOV=37.5 degrees. When a maximum refractive index of one single lens element among the first lens element 110, the second lens element 120, the third lens element 130, the fourth lens element 140, the fifth lens element 150, the sixth lens element 160 and the seventh lens element 170 is Nmax, the following condition is satisfied: Nmax=1.63. When a minimum refractive index of one single lens element among the first lens element 110, the second lens element 120, the third lens element 130, the fourth lens element 140, the fifth lens element 150, the sixth lens element 160 and the seventh lens element 170 is Nmin, the following condition is satisfied: Nmin=1.54. When an Abbe number of the sixth lens element 160 is V6, the following condition is satisfied: V6=23.4. When an Abbe number of the first lens element 110 is V1, an Abbe number of the second lens element 120 is V2, an Abbe number of the fifth lens element 150 is V5, the Abbe number of the sixth lens element 160 is V6, the following condition is satisfied: (V1+V2)/(V5+V6)=2.39. When a central thickness of the sixth lens element 160 is CT6, a central thickness of the seventh lens element 170 is CT7, the following condition is satisfied: CT6/CT7=1.14. When a sum of central thicknesses of the first lens element 110 through the seventh lens element 170 is ΣCT, an axial distance between the object-side surface 111 of the first lens element 110 and the image-side surface 172 of the seventh lens element 170 is Td, the following condition is satisfied: ΣCT/Td=0.634. When a curvature radius of the image surface 190 of the photographing optical lens assembly is Rimg, the following condition is satisfied: Rimg=∞[mm]. When the focal length of the photographing optical lens assembly is f, a curvature radius of the image-side surface 172 of the seventh lens element 170 is R14, the following condition is satisfied: R14/f=0.41. When the focal length of the photographing optical lens assembly is f, a composite focal length of the first lens element 110 and the second lens element 120 is f12, the following condition is satisfied: f/f12=1.05. When the focal length of the photographing optical lens assembly is f, a focal length of the sixth lens element 160 is f6, the following condition is satisfied: f6/f=−4.00. When the focal length of the photographing optical lens assembly is f, the focal length of the sixth lens element 160 is f6, a focal length of the seventh lens element 170 is f7, the following condition is satisfied: (f/f6)+(f/f7)=−1.46. When an axial distance between the image-side surface 172 of the seventh lens element 170 and the image surface 190 is BF, the focal length of the photographing optical lens assembly is f, the following condition is satisfied: BF/f=0.21. When a maximum image height of the photographing optical lens assembly is ImgH, an axial distance between the object-side surface 111 of the first lens element 110 and the image surface 190 is TL, the following condition is satisfied: TL/ImgH=1.73. When the axial distance between the object-side surface 111 of the first lens element 110 and the image-side surface 172 of the seventh lens element 170 is Td, an entrance pupil diameter of the photographing optical lens assembly is EPD, the following condition is satisfied: Td/EPD=2.29. The detailed optical data of the 1st embodiment are shown in Table 1 and the aspheric surface data are shown in Table 2 below. TABLE 1 1st Embodiment f = 5.30 mm, Fno = 2.10, HFOV = 37.5 deg. Focal Surface# Curvature Radius Thickness Material Index Abbe # Length 0 Object Plano Infinity 1 Ape. Stop Plano −0.308 2 Lens 1 2.654 (ASP) 0.452 Plastic 1.544 55.9 14.85 3 3.716 (ASP) 0.059 4 Lens 2 3.744 (ASP) 0.625 Plastic 1.544 55.9 7.14 5 96.858 (ASP) 0.069 6 Lens 3 2.738 (ASP) 0.260 Plastic 1.633 23.4 −10.10 7 1.846 (ASP) 0.722 8 Lens 4 ∞ (ASP) 0.963 Plastic 1.544 55.9 3.00 9 −1.633 (ASP) 0.078 10 Lens 5 −1.256 (ASP) 0.614 Plastic 1.633 23.4 −58.83 11 −1.547 (ASP) 0.062 12 Lens 6 −3.216 (ASP) 0.400 Plastic 1.633 23.4 −21.22 13 −4.433 (ASP) 1.121 14 Lens 7 27.704 (ASP) 0.350 Plastic 1.535 55.7 −4.38 15 2.151 (ASP) 0.600 16 IR-cut filter Plano 0.200 Glass 1.517 64.2 — 17 Plano 0.325 18 Image Plano — Note: Reference wavelength is 587.6 nm (d-line). TABLE 2 Aspheric Coefficients Surface # 2 3 4 5 6 k = −3.5617E+00 −2.0000E+01 −2.8093E+00 −1.0000E+00 −1.0472E+00 A4 = 1.4436E−02 −1.1067E−02 −3.7250E−02 5.5248E−03 −8.0256E−02 A6 = 5.6396E−03 8.0140E−03 2.9977E−02 −6.5500E−03 3.1166E−02 A8 = −5.7355E−03 −3.9058E−03 −2.0926E−02 1.6038E−03 −2.7591E−02 A10 = 1.8196E−03 4.4662E−03 1.2453E−02 −6.8835E−03 1.5033E−02 A12 = 9.7976E−04 8.0133E−04 −4.8342E−04 6.1358E−03 −5.0952E−03 A14 = −4.8334E−04 −4.1346E−04 −1.4700E−03 −2.2356E−03 1.1335E−03 A16 = 6.0586E−05 −9.3249E−05 2.0429E−04 2.2791E−04 −1.2196E−04 Surface # 7 8 9 10 11 k = −1.7034E+00 −1.0000E+00 −4.5573E+00 −1.9931E+00 −2.3831E+00 A4 = −6.4892E−02 −1.5344E−02 −4.0939E−03 1.1503E−01 7.5666E−02 A6 = 3.3539E−02 −1.4815E−02 −3.5512E−02 −8.2179E−02 −3.1274E−02 A8 = −1.5958E−02 1.6363E−02 2.7556E−02 4.2696E−02 1.0700E−02 A10 = 5.2506E−03 −1.2418E−02 −1.2172E−02 −1.5553E−02 −4.1447E−03 A12 = −6.3505E−04 6.1466E−03 3.3438E−03 3.4548E−03 8.1224E−04 A14 = −4.8209E−05 −1.7585E−03 −5.2931E−04 −3.7288E−04 −6.0865E−05 A16 = 2.3866E−05 2.0236E−04 4.0681E−05 1.1639E−05 8.6034E−07 Surface # 12 13 14 15 k = −2.0000E+01 7.5348E−01 −6.1423E+00 −6.2822E+00 A4 = −2.5444E−02 −7.4794E−03 −6.4411E−02 −3.5213E−02 A6 = 5.9287E−03 −6.9438E−03 1.1584E−02 8.5452E−03 A8 = 2.4093E−03 9.5491E−03 −9.4024E−04 −1.6035E−03 A10 = −1.4394E−03 −3.6088E−03 4.1629E−05 1.9535E−04 A12 = −5.3124E−05 6.7027E−04 −1.0641E−06 −1.5661E−05 A14 = 7.1367E−05 −6.2123E−05 1.8240E−08 7.3114E−07 A16 = −6.2088E−06 2.2913E−06 −2.5563E−10 −1.4448E−08 In Table 1, the curvature radius, the thickness and the focal length are shown in millimeters (mm). Surface numbers 0-18 represent the surfaces sequentially arranged from the object-side to the image-side along the optical axis. In Table 2, k represents the conic coefficient of the equation of the aspheric surface profiles. A4-A16 represent the aspheric coefficients ranging from the 4th order to the 16th order. The tables presented below for each embodiment are the corresponding schematic parameter and aberration curves, and the definitions of the tables are the same as Table 1 and Table 2 of the 1st embodiment. Therefore, an explanation in this regard will not be provided again. 2nd Embodiment FIG. 3 is a schematic view of an image capturing unit according to the 2nd embodiment of the present disclosure. FIG. 4 shows, in order from left to right, spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 2nd embodiment. In FIG. 3, the image capturing unit includes the photographing optical lens assembly (its reference numeral is omitted) of the present disclosure and an image sensor 295. The photographing optical lens assembly includes, in order from an object side to an image side an aperture stop 200, a first lens element 210, a second lens element 220, a third lens element 230, a fourth lens element 240, a fifth lens element 250, a sixth lens element 260, a seventh lens element 270, an IR-cut filter 280 and an image surface 290, wherein the photographing optical lens assembly has a total of seven lens elements (210-270) with refractive power. There is an air gap in a paraxial region between any two of the first lens element 210, the second lens element 220, the third lens element 230, the fourth lens element 240, the fifth lens element 250, the sixth lens element 260 and the seventh lens element 270 that are adjacent to each other. The first lens element 210 with positive refractive power has an object-side surface 211 being convex in a paraxial region thereof and an image-side surface 212 being concave in a paraxial region thereof. The first lens element 210 is made of plastic material and has the object-side surface 211 and the image-side surface 212 being both aspheric. The second lens element 220 with positive refractive power has an object-side surface 221 being convex in a paraxial region thereof and an image-side surface 222 being convex in a paraxial region thereof. The second lens element 220 is made of plastic material and has the object-side surface 221 and the image-side surface 222 being both aspheric. The third lens element 230 with negative refractive power has an object-side surface 231 being convex in a paraxial region thereof and an image-side surface 232 being concave in a paraxial region thereof. The third lens element 230 is made of plastic material and has the object-side surface 231 and the image-side surface 232 being both aspheric. The fourth lens element 240 with positive refractive power has an object-side surface 241 being convex in a paraxial region thereof and an image-side surface 242 being convex in a paraxial region thereof. The fourth lens element 240 is made of plastic material and has the object-side surface 241 and the image-side surface 242 being both aspheric. The fifth lens element 250 with positive refractive power has an object-side surface 251 being concave in a paraxial region thereof and an image-side surface 252 being convex in a paraxial region thereof. The fifth lens element 250 is made of plastic material and has the object-side surface 251 and the image-side surface 252 being both aspheric. The sixth lens element 260 with negative refractive power has an object-side surface 261 being concave in a paraxial region thereof and an image-side surface 262 being convex in a paraxial region thereof. The image-side surface 262 of the sixth lens element 260 has at least one concave shape in an off-axis region thereof. The sixth lens element 260 is made of plastic material and has the object-side surface 261 and the image-side surface 262 being both aspheric. The seventh lens element 270 with negative refractive power has an object-side surface 271 being concave in a paraxial region thereof and an image-side surface 272 being concave in a paraxial region thereof. The image-side surface 272 of the seventh lens element 270 has at least one convex shape in an off-axis region thereof. The sixth lens element 270 is made of plastic material and has the object-side surface 271 and the image-side surface 272 being both aspheric. The IR-cut filter 280 is made of glass and located between the seventh lens element 270 and the image surface 290, and will not affect the focal length of the photographing optical lens assembly. The image sensor 295 is disposed on or near the image surface 290 of the photographing optical lens assembly. The detailed optical data of the 2nd embodiment are shown in Table 3 and the aspheric surface data are shown in Table 4 below. TABLE 3 2nd Embodiment f = 4.88 mm, Fno = 1.85, HFOV = 38.7 deg. Focal Surface# Curvature Radius Thickness Material Index Abbe # Length 0 Object Plano Infinity 1 Ape. Stop Plano −0.345 2 Lens 1 2.492 (ASP) 0.498 Plastic 1.544 55.9 10.54 3 4.096 (ASP) 0.100 4 Lens 2 5.326 (ASP) 0.664 Plastic 1.544 55.9 7.30 5 −14.943 (ASP) 0.050 6 Lens 3 3.018 (ASP) 0.260 Plastic 1.639 23.5 −8.91 7 1.906 (ASP) 0.631 8 Lens 4 29.807 (ASP) 0.944 Plastic 1.544 55.9 3.52 9 −2.022 (ASP) 0.067 10 Lens 5 −1.642 (ASP) 0.650 Plastic 1.639 23.5 28.48 11 −1.738 (ASP) 0.229 12 Lens 6 −3.652 (ASP) 0.400 Plastic 1.639 23.5 −46.87 13 −4.337 (ASP) 0.509 14 Lens 7 −90.991 (ASP) 0.500 Plastic 1.583 30.2 −3.46 15 2.068 (ASP) 0.500 16 IR-cut filter Plano 0.300 Glass 1.517 64.2 — 17 Plano 0.299 18 Image Plano — Note: Reference wavelength is 587.6 nm (d-line). TABLE 4 Aspheric Coefficients Surface # 2 3 4 5 6 k = −2.7451E+00 −1.9655E+01 −2.5770E−01 −1.0000E+00 −1.3273E+00 A4 = 1.0276E−02 −1.7113E−02 −4.1113E−02 7.6708E−03 −8.0332E−02 A6 = 5.0161E−03 6.7710E−03 2.4687E−02 −9.8820E−03 2.8575E−02 A8 = −4.7219E−03 −4.9153E−03 −1.7480E−02 5.2450E−03 −2.7172E−02 A10 = 7.5324E−04 4.9011E−03 1.2130E−02 −7.4098E−03 1.5269E−02 A12 = 7.7979E−04 5.1669E−04 −7.7254E−04 5.3379E−03 −5.2607E−03 A14 = −2.5945E−04 −5.7063E−04 −1.4847E−03 −2.1020E−03 9.8332E−04 A16 = 9.9514E−06 −5.1546E−06 2.6379E−04 2.9899E−04 −4.1982E−05 Surface # 7 8 9 10 11 k = −2.1251E+00 −1.0000E+00 −3.6390E+00 −1.7015E+00 −1.6803E+00 A4 = −6.5141E−02 −1.2916E−02 4.6925E−02 1.1659E−01 7.6154E−02 A6 = 3.3547E−02 −3.7104E−04 −6.9878E−02 −8.2545E−02 −3.1006E−02 A8 = −1.6516E−02 −5.0636E−04 4.9275E−02 4.2257E−02 1.0306E−02 A10 = 5.6137E−03 7.1659E−04 −2.5903E−02 −1.5583E−02 −4.0548E−03 A12 = −6.7538E−04 2.1274E−04 9.7449E−03 3.4836E−03 8.4339E−04 A14 = −7.2308E−05 −3.5062E−04 −2.1545E−03 −3.6424E−04 −5.9982E−05 A16 = 3.2881E−05 5.5234E−05 1.9954E−04 1.0294E−05 −2.0939E−07 Surface # 12 13 14 15 k = −2.0000E+01 6.5216E−01 4.7498E+00 −7.1215E+00 A4 = −2.7210E−02 −3.1242E−02 −1.0723E−01 −3.8828E−02 A6 = 2.8341E−02 2.1812E−02 2.6057E−02 8.0516E−03 A8 = −1.8703E−02 −7.3064E−03 −2.1234E−03 −8.5785E−04 A10 = 6.5928E−03 1.1931E−03 −2.6011E−05 2.0475E−05 A12 = −1.6661E−03 −4.3125E−05 1.4789E−05 2.7881E−06 A14 = 2.3570E−04 −8.4472E−06 −8.2708E−07 −1.7148E−07 A16 = −1.2301E−05 6.7621E−07 1.3310E−08 1.9342E−09 In the 2nd embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the 1st embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the 1st embodiment with corresponding values for the 2nd embodiment, so an explanation in this regard will not be provided again. Moreover, these parameters can be calculated from Table 3 and Table 4 as the following values and satisfy the following conditions: 2nd Embodiment f [mm] 4.88 Rimg [mm] ∞ Fno 1.85 R14/f 0.42 HFOV [deg.] 38.7 f/f12 1.07 Nmax 1.64 f6/f −9.60 Nmin 1.54 (f/f6) + (f/f7) −1.51 V6 23.5 BF/f 0.23 (V1 + V2)/(V5 + V6) 2.38 TL/ImgH 1.65 CT6/CT7 0.80 Td/EPD 2.09 ΣCT/Td 0.712 3rd Embodiment FIG. 5 is a schematic view of an image capturing unit according to the 3rd embodiment of the present disclosure. FIG. 6 shows, in order from left to right, spherical aberration curves, astigmatic field curves and a distortion curve of the image capturing unit according to the 3rd embodiment. In FIG. 5, the image capturing unit includes the photographing optical lens assembly (its reference numeral is omitted) of the present disclosure and an image sensor 395. The photographing optical lens assembly includes, in order from an object side to an image side, an aperture stop 300, a first lens element 310, a second lens element 320, a third lens element 330, a fourth lens element 340, a fifth lens element 350, a sixth lens element 360, a seventh lens element 370, an IR-cut filter 380 and an image surface 390, wherein the photographing optical lens assembly has a total of seven lens elements (310-370) with refractive power. There is an air gap in a paraxial region between any two of the first lens element 310, the second lens element 320, the third lens element 330, the fourth lens element 340, the fifth lens element 350, the sixth lens element 360 and the seventh lens element 370 that are adjacent to each other. The first lens element 310 with positive refractive power has an object-side surface 311 being convex in a paraxial region thereof and an image-side surface 312 being concave in a paraxial region thereof. The first lens element 310 is made of plastic material and has the object-side surface 311 and the image-side surface 312 being both aspheric. The second lens element 320 with positive refractive power has an object-side surface 321 being concave in a paraxial region thereof and an image-side surface 322 being convex in a paraxial region thereof. The second lens element 320 is made of plastic material and has the object-side surface 321 and the image-side surface 322 being both aspheric. The third lens element 330 with negative refractive power has an object-side surface 331 being convex in a paraxial region thereof and an image-side surface 332 being concave in a paraxial region thereof. The third lens element 330 is made of plastic material and has the object-side surface 331 and the image-side surface 332 being both aspheric. The fourth lens element 340 with positive refractive power has an object-side surface 341 being convex in a paraxial region thereof and an image-side surface 342 being convex in a paraxial region thereof. The fourth lens element 340 is made of plastic material and has the object-side surface 341 and the image-side surface 342 being both aspheric. The fifth lens element 350 with negative refractive power has an object-side surface 351 being concave in a paraxial region thereof and an image-side surface 352 being convex in a paraxial region thereof. The fifth lens element 350 is made of plastic material and has the object-side surface 351 and the image-side surface 352 being both aspheric. The sixth lens element 360 with negative refractive power has an object-side surface 361 being concave in a paraxial region thereof and an image-side surface 362 being convex in a paraxial region thereof. The image-side surface 362 of the sixth lens element 360 has at least one concave shape in an off-axis region thereof. The sixth lens element 360 is made of plastic material and has the object-side surface 361 and the image-side surface 362 being both aspheric. The seventh lens element 370 with negative refractive power has an object-side surface 371 being concave in a paraxial region thereof and an image-side surface 372 being concave in a paraxial region thereof. The image-side surface 372 of the seventh lens element 370 has at least one convex shape in an off-axis region thereof. The sixth lens element 370 is made of plastic material and has the object-side surface 371 and the image-side surface 372 being both aspheric. The IR-cut filter 380 is made of glass and located between the seventh lens element 370 and the image surface 390, and will not affect the focal length of the photographing optical lens assembly. The image sensor 395 is disposed on or near the image surface 390 of the photographing optical lens assembly. The detailed optical data of the 3rd embodiment are shown in Table 5 and the aspheric surface data are shown in Table 6 below. TABLE 5 3rd Embodiment f = 5.38 mm, Fno = 1.73, HFOV = 36.8 deg. Focal Surface# Curvature Radius Thickness Material Index Abbe # Length 0 Object Plano Infinity 1 Ape. Stop Plano −0.519 2 Lens 1 2.654 (ASP) 0.687 Plastic 1.544 55.9 5.82 3 14.875 (ASP) 0.050 4 Lens 2 −96.942 (ASP) 0.526 Plastic 1.514 56.8 97.14 5 −32.999 (ASP) 0.050 6 Lens 3 2.864 (ASP) 0.330 Plastic 1.640 23.3 −10.49 7 1.917 (ASP) 0.577 8 Lens 4 18.964 (ASP) 1.187 Plastic 1.544 55.9 3.05 9 −1.776 (ASP) 0.071 10 Lens 5 −1.409 (ASP) 0.643 Plastic 1.640 23.3 −23.83 11 −1.829 (ASP) 0.050 12 Lens 6 −8.873 (ASP) 0.400 Plastic 1.640 23.3 −27.83 13 −17.994 (ASP) 1.073 14 Lens 7 −32.658 (ASP) 0.500 Plastic 1.535 55.7 −4.40 15 2.551 (ASP) 0.500 16 IR-cut filter Plano 0.300 Glass 1.517 64.2 — 17 Plano 0.252 18 Image Plano — Note: Reference wavelength is 587.6 nm (d-line). TABLE 6 Aspheric Coefficients Surface # 2 3 4 5 6 k = −1.7181E+00 1.1104E+00 −2.0000E+01 −1.0000E+00 −8.9149E−02 A4 = 9.5611E−03 −2.4090E−02 −3.4435E−03 3.6835E−02 −7.0674E−02 A6 = 3.7019E−03 1.8135E−02 2.0716E−02 −1.3171E−02 2.5334E−02 A8 = −2.1882E−03 −7.5777E−03 −1.6290E−02 4.7648E−03 −2.6272E−02 A10 = 1.6773E−04 5.4750E−03 1.1487E−02 −6.6511E−03 1.4841E−02 A12 = 5.6189E−04 5.6842E−04 −5.6982E−04 5.3854E−03 −5.2035E−03 A14 = −1.6823E−04 −7.5474E−04 −1.2285E−03 −2.1163E−03 1.0445E−03 A16 = 1.2862E−05 7.4297E−05 2.3330E−04 3.5464E−04 −7.4689E−05 Surface # 7 8 9 10 11 k = −1.9940E+00 −1.0000E+00 −3.4848E+00 −1.3857E+00 −3.6772E+00 A4 = −5.7775E−02 −9.4863E−03 8.5885E−03 1.2328E−01 5.9384E−02 A6 = 3.3846E−02 3.0457E−03 −2.9727E−02 −7.7829E−02 −3.0931E−02 A8 = −1.8688E−02 −1.0812E−02 1.7657E−02 4.2569E−02 1.1483E−02 A10 = 5.8132E−03 1.3845E−02 −2.4281E−03 −1.5673E−02 −3.9964E−03 A12 = −5.0051E−04 −8.6161E−03 −1.5652E−03 3.4435E−03 8.0624E−04 A14 = −6.4496E−05 2.5655E−03 6.3476E−04 −3.7128E−04 −6.7726E−05 A16 = 3.2961E−06 −2.8547E−04 −6.4192E−05 1.1565E−05 7.2106E−07 Surface # 12 13 14 15 k = −9.9342E+00 −2.0000E+01 2.6238E+00 −9.2828E+00 A4 = −1.3120E−02 −6.5533E−02 −8.3641E−02 −3.3705E−02 A6 = 4.5857E−03 3.0002E−02 1.6838E−02 7.2650E−03 A8 = −7.5794E−03 −1.1493E−02 −6.8703E−04 −9.9339E−04 A10 = 4.3871E−03 2.9666E−03 −1.7616E−04 8.0847E−05 A12 = −1.5578E−03 −4.1297E−04 2.9158E−05 −3.9800E−06 A14 = 2.7939E−04 2.8544E−05 −1.8236E−06 1.1008E−07 A16 = −1.8643E−05 −7.8531E−07 4.3320E−08 −1.3508E−09 In the 3rd embodiment, the equation of the aspheric surface profiles of the aforementioned lens elements is the same as the equation of the 1st embodiment. Also, the definitions of these parameters shown in the following table are the same as those stated in the 1st embodiment with corresponding values for the 3rd embodiment, so an explanation in this regard will not be provided again. Moreover, these parameters can be calculated from Table 5 and Table 6 as the following values and satisfy the following conditions: 3rd Embodiment f [mm] 5.38 Rimg [mm] ∞ Fno 1.73 R14/f 0.47 HFOV [deg.] 36.8 f/f12 0.97 Nmax 1.64 f6/f −5.17 Nmin 1.51 (f/f6) + (f/f7) −1.42 V6 23.3 BF/f 0.20 (V1 + V2)/(V5 + V6) 2.42 TL/ImgH 1.80 CT6/CT7 0.80 Td/EPD 1.98 ΣCT/Td 0.695 4th Embodiment FIG. 7 is a schematic view of an image capturing unit according to the 4th embodiment of the present
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