A key step for the singlet oxygen formation is the ISC of the photosensitizer, populating the triplet states (Scheme 1, reaction 2b). Therefore, it is essential to evaluate the ISC rates of the derivatives. After excitation to their bright states, the compounds would typically vibrationally relax to the S1 excited state, following Kasha's rule. From the S1 state minimum, fluorescence and intersystem crossing can compete (reactions 2a and 2b). To evaluate which compounds under study would be more prone for singlet oxygen generation upon excitation of trans-resveratrol, we calculated their fluorescence and ISC rates.