Solvent dielectric delimited nitro–nitrito photorearrangement in a perylenediimide derivative

Abstract

Vibrant excited-state dynamics, in conjunction with distinctive photochemistry has established nitrated-polycyclic aromatic hydrocarbons as an exhilarating class of organic compounds. Herein, we report the atypical photorearrangement of nitro-perylenediimide (NO2-PDI) to nitrito-perylenediimide (ONO-PDI), giving rise to linkage isomers in polar aprotic acetonitrile solvent triggered by visible-light excitation. ONO-PDI has been isolated and unambiguously characterized using standard spectroscopic, spectrometric and elemental composition techniques. Although nitritoaromatic compounds are conventionally considered as crucial intermediates in the photodissociation of nitroaromatics, the experimental evidences for the same are not observed heretofore. Ultrafast transient absorption spectroscopy equipped with computational investigations revealed the prominence of a conformationally relaxed singlet excited-state (S_1^CR) of NO2-PDI in the photoisomerization pathway. Theoretical transition state (TS) analysis displayed the presence of a 6-membered cyclic TS, pivotal in connecting the S_1^CR state to the photoproduct state. This article addresses the prevailing knowledge gaps in the field of organic linkage isomers and provides a comprehensive understanding of the unprecedented photoisomerization mechanism operating in NO2-PDI.