Reversible fluorescence modulation through the photoisomerization of an azobenzene-bridged perylene bisimide cyclophane

Abstract

A new type of perylene bisimide (PBI) cyclophane in which two PBI chromophores were linked via an azobenzene (Azo) bridge was designed and synthesized. It was found that the integration of electron-donating azobenzene and electron-deficient PBI in a well-defined cyclophane enables the regulation of the fluorescence lifetime and quantum yield of the PBI units. With the aid of a high efficiency trans → cis transformation of the azobenzene moiety, the PBI–PBI chromophore distance can be effectively controlled as revealed by exciton coupling and density functional theory (DFT) computation, leading to additional non-radiative decay pathways and a pronounced fluorescence quenching due to cooperative adjustments of PBI–PBI and PBI–Azo interactions. Reversible fluorescence intensity switching for at least five cycles was successfully achieved with alternate UV and visible light irradiation. These well-controlled fluorescence modulation and photoswitching behaviours not only provide insights into interchromophoric interactions but also contribute to the development of stimuli-responsive luminescent macrocycles.