Effect of structural bending on the photophysical properties of perylene bisimide

The effect of nonplanarity on the electronic properties of π-systems has been difficult to study systematically because of the limited availability of suitable model compounds. Our group recently synthesized a series of end-to-end bent perylene bisimide (PBI) cyclophanes, whose degree of bending is adjustable by modifying the internal alkyl tethers. Herein, we subjected these bent PBI derivatives to theoretical calculations and time-resolved spectroscopy. The current study has offered rational explanations for several unique photophysical characteristics of bent PBIs: (1) the redshifts of the S0-S1 transitions, (2) the decrease in extinction coefficients, (3) the broadening of spectral shapes, and (4) the suppression of nonradiative decay processes. Furthermore, the investigation of the S1 states and radical anions has revealed that structural bending also substantially alters the energy levels of upper molecular orbitals such as LUMO+2.