Inside Cover: Molecular Polygons Probe the Role of Intramolecular Strain in the Photophysics of π‐Conjugated Chromophores (Angew. Chem. Int. Ed. 5/2017)

Abstract

p-Conjugated segments,chromophores,are the electronically active units of polymer materials used in organic electronics.Toelucidate the effect of the bending of these linear moieties on elementary electronic properties,such as lumines-cence color and radiative rate,weintroduce aseries of molecular polygons.The p-system in these molecules becomes so distorted in bichromophores (digons) that these absorb and emit light of arbitrary polarization:any part of the chain absorbs and emits radiation with equal probability.Bending leads to acancellation of transition dipole moment (TDM), increasing excited-state lifetime.Simultaneously,fluorescence shifts to the red as radiative transitions require mixing of the excited state with vibrational modes.However,strain can become so large that excited-state localization on shorter units of the chain occurs,compensating TDM cancellation. The underlying correlations between shape and photophysics can only be resolved in single molecules.