Density Functional Theory (DFT) calculation was performed to obtain a comprehensive understanding of the molecular structure and photophysical properties. As shown in Figure , the two molecules afforded similar molecular geometries. The benzoselenadiazole and thiophene unit gave a relatively small dihedral angles between TPE and the adjacent onium salt ring, such good conjugation facilitated efficient intramolecular charge transfer (ICT) between the donor and acceptor units. Other phenyl rings in TPE segment afforded highly twisted conformation, which is favorable for solid-state emission. The electrons of the lowest unoccupied molecular orbital (LUMO) of TPE-Py is primarily situated at the electronwithdrawing pyridinium and benzoselenadiazole group, while the highest occupied molecular orbital (HOMO) located on the TPE segment, implying an effective ICT effect. TPE-Qu exhibited a similar electronic distribution (Figure ). Moreover, the energy gap between singlet and triplet states (ΔEST) of TPE-Py and TPE-Qu were calculated (Figure and).