Multifunctionality is one of the main goals and a great promise of materials science. It is also a hot topic in the subfield of molecular materials which promises to deliver single molecules with multiple intertwined functions. The multifunctionality in molecule-based systems can be achieved by a rational design/choice of building blocks and their smart assembly into various classes of molecules and molecular solids ranging from purely organic compounds and mononuclear coordination complexes to sophisticated multi-dimensional polymeric structures including coordination polymers. One of the many classes of multifunctional molecule-based compounds are magnets responsive to visible light -molecular photomagnets. Photomagnets enable the control of the magnetic properties by photons -a feature that can be achieved by design in molecular systems but is hardy accessible in conventional magnetic materials except some orthoferrites and transparent films of some garnets. One of the strategies towards photomagnetic compounds is the incorporation of photochromic molecules widely used by Feringa et al. to achieve unique photomechanical properties and by Lehn et al. for photo-and electroswitchable molecular devices. Such molecules coordinated to paramagnetic centers enable the control of the magnetic properties of the resulting compound upon reversible photoisomerization reaction of the ligand. The control occurs either through the modification of the magnetic interaction pathways -the two photoisomers need to transmit these interaction differently or by influencing the coordination geometry of the paramagnetic species. Dithienylethenes (a subgroup of diarylethenes ) seem to be the most widely used photochromic ligands for the construction of photomagnetic assemblies. Some of the current trends in the field of molecular photomagnets focus on the incorporation of the photoswitching functionality into lanthanide single molecule magnets (Ln-SMMs) -compounds that show magnetization blocking below a certain blocking temperature TB. The use of photochromic ligands in the construction of Ln-SMMs allows the control of various magnetization relaxation mechanisms -usually the quantum tunneling of magnetization. However, the main targets are the temperature-dependent relaxation mechanisms: Raman and Orbach. To the best of our knowledge, all photochromic Ln-SMM systems are based on Ln centers with high coordination numbers, which make their design challenging and serendipitous according to the Ln-SMM design strategies proposed by Tong and co-workers. Herein, we take an approach where a low-coordinate lanthanide complex showing SMM behavior, is approached only by one or two monodentate weak-field ligands so that the SMM character of the parent compound is retained and enriched by an additional functionality. This strategy was proposed by some of us previously and demonstrated by the substitution of THF by the TEMPO molecule in the structure of [Er III (BHT)3(THF)] (BHT = 2,6-di-tert-butyl-4-methylphenolate). In this work particularly, the four-coordinate [Er III (BHT)3(THF)] and the three-coordinate Er III complex [Er III (BHT)3] are reacted with two types of N-donor diarylethene-type bridging ligands that are wellknown to undergo photoisomerization: 1,2-bis(2-methyl-5-pyridyl)thie-3-yl)perfluorocyclopentene (dtepy) and 4,4'-azopyridine (azopy). The respective reactions yield two coordination species: the trinuclear linear {[Er III (BHT)3]3(dtepy)2} . 3C5H12 complex (1) and a coordination chain {[Er III (BHT)3(azopy)2C5H12}n (2). The reaction takes place in a strictly non-coordinating solvent -n-pentane -with a strictly controlled number of bridging ligands. Hence, the coordination number of the Er III centers increases in a controlled manner from 3 to 4 and 5 in compound 1 and from 3 to 5 in compound 2. As aforementioned, this strategy enables the retention of the SMM functionality and the observation of the photoisomerization associated with dtepy ligand in compound 1, while compound 2 remains unresponsive to light, most probably due to the more rigid chain structure. The combination of both functionalities: the SMM-type slow magnetic relaxation and the reversible ligand photoisomerization are presented and discussed.