Two benzotriazole derivatives, 2-benzyl-4,7-di(thiophen-2-yl)-2H-benzo[d][1,2,3] triazole (BBTS) and 2-benzyl-4,7-bis(2,3-dihydrothieno[3,4-b][1,4] dioxin-5-yl)-2H-benzo[d] [1,2,3] triazole (BBTES) were employed as photosensitizers for diaryliodonium salt photoinitiators in photoinitiated cationic polymerization of various epoxide and vinyl ether monomers. Diphenyliodonium hexafluorophosphate (Ph2I+PF6-) salt was used as the photoinitiator in this study. Extended conjugation and electron-rich moieties of the photosensitizers enabled the use of long wavelength UV and visible light emitting light sources in cationic photopolymerizations. Having low oxidation potentials and good solubility in cationically polymerizable monomers make them efficient photosensitizers for the diphenyliodonium salt in the photoinitiated cationic polymerization. Polymerizations were achieved at room temperature and monitored by optical pyrometry. Moreover, photopolymerization of a diepoxide monomer with ambient solar irradiation in the presence of BBTES and BBTS were examined.