Bending‐Induced Vibrational Landscape Reorganization Governs Energy Dissipation in Perylene Bisimides

Abstract

ABSTRACT Structural distortion is widely recognized to suppress emissions in organic chromophores; however, the mechanistic origin of the associated enhancement in nonradiative decay remains unresolved. Here, we employ a series of perylene bisimide derivatives with systematically controlled bending to directly elucidate the structural origin of distortion‐enhanced nonradiative relaxation. A pronounced transition is observed from near‐unity emission to strongly enhanced nonradiative decay within the singlet manifold, while intersystem crossing remains negligible. Time‐resolved electronic spectroscopy excludes triplet‐mediated pathways and establishes internal conversion as the dominant decay channel. Crucially, time‐resolved Raman measurements provide direct insight into the underlying structural dynamics, revealing that bending suppresses the electronically coupled aromatic skeletal mode, reorganizes the low‐frequency vibrational manifold, and accelerates vibrational dephasing. The results herein demonstrate that bending enhances internal conversion not primarily through energy‐gap reduction, but by transforming the excited‐state vibrational landscape into a more dissipative environment that facilitates efficient energy relaxation. More broadly, this work identifies vibrational dissipation and coherence loss as key determinants of nonradiative decay and establishes a general structure–vibrational dynamics framework for controlling excited‐state energy flow in π‐conjugated systems.