Exciton Localization in Extended 蟺-Electron Systems: Comparison of Linear and Cyclic Structures

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• 作者：Alexander Thiessen ; Dominik W眉rsch ; Stefan-S. Jester ; A. Vikas Aggarwal ; Alissa Idelson ; Sebastian Bange ; Jan Vogelsang ; Sigurd H枚ger ; John M. Lupton
• 刊名：Journal of Physical Chemistry B
• 出版年：2015
• 出版时间：July 30, 2015
• 年：2015
• 卷：119
• 期：30
• 页码：9949-9958
• 全文大小：542K
• ISSN：1520-5207

文摘

We employ five 蟺-conjugated model materials of different molecular shape鈥攐ligomers and cyclic structures鈥攖o investigate the extent of exciton self-trapping and torsional motion of the molecular framework following optical excitation. Our studies combine steady state and transient fluorescence spectroscopy in the ensemble with measurements of polarization anisotropy on single molecules, supported by Monte Carlo simulations. The dimer exhibits a significant spectral red shift within 鈭?00 ps after photoexcitation which is attributed to torsional relaxation. This relaxation mechanism is inhibited in the structurally rigid macrocyclic analogue. However, both systems show a high degree of exciton localization but with very different consequences: while, in the macrocycle, the exciton localizes randomly on different parts of the ring, scrambling polarization memory, in the dimer, localization leads to a deterministic exciton position with luminescence characteristics of a dipole. Monte Carlo simulations allow us to quantify the structural difference between the emitting and absorbing units of the 蟺-conjugated system in terms of disorder parameters.