The spin dynamics of photoconductive tetrathiafulvalene (TTF) derivatives containing 2,5-diphenyl-1,3,4-oxadiazole (PPD) was examined using time-resolved electron spin resonance (TR-ESR) spectroscopy. TR-ESR signals of a frozen solution sample under visible excitation were attributed to the excited triplet state T1, which was populated via intersystem crossing from the excited singlet state S1 as confirmed by TR-ESR spectral simulations. From DFT calculations, the spin-density distribution of the T1 state was found to be concentrated around the linker between the TTF and PPD molecules.