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Molecular Polygons Probe the Role of Intramolecular Strain in the Photophysics of π‐Conjugated Chromophores
Author(s) -
Wilhelm Philipp,
Vogelsang Jan,
Poluektov Georgiy,
Schönfelder Nina,
Keller Tristan J.,
Jester StefanSven,
Höger Sigurd,
Lupton John M.
Publication year - 2017
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201610723
Subject(s) - chromophore , excited state , intramolecular force , transition dipole moment , conjugated system , luminescence , photochemistry , dipole , molecule , fluorescence , radiative transfer , chemistry , molecular physics , spontaneous emission , polarization (electrochemistry) , materials science , chemical physics , atomic physics , polymer , optoelectronics , optics , physics , laser , stereochemistry , organic chemistry
π‐Conjugated segments, chromophores, are the electronically active units of polymer materials used in organic electronics. To elucidate the effect of the bending of these linear moieties on elementary electronic properties, such as luminescence color and radiative rate, we introduce a series of molecular polygons. The π‐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 a cancellation 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.