Oxygen-Mediated Sequential Down-Conversion in Perylenediimides

Abstract

Perylenediimides (PDIs) are among the best-known chromophores for optoelectronic applications. Their photophysics in oxygen-rich environments remains, however, underexplored. In this study, we investigate three different PDI derivatives using steady-state and time-resolved absorption and emission spectroscopy in toluene with different oxygen concentrations. Unsubstituted PDI and 1,7-bay-substituted PDI featuring diphenylphenoxy groups exhibit oxygen-mediated sequential down-conversion. Upon photoexcitation, the singlet excited state (S1) of PDIs interacts with molecular oxygen (3O2) to generate singlet oxygen (1O2) via the formation of the triplet excited state (T1) of PDIs. Subsequently, (T1)s of PDIs sensitize an additional 3O2 to produce a second 1O2. Overall, one (S1) produces two 1O2. Importantly, this process depends on energy requirements: on one hand, the energy difference between (S1) and (T1), and on the other hand, the (T1) energy level should exceed that of 1O2. Our work illustrates the oxygen-mediated sequential down-conversion in perylenediimides and reveals its effects.