Ultrafast Excited State Dynamics in 9,9鈥?Bifluorenylidene

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• 作者：Jamie Conyard ; Ismael A. Heisler ; Wesley R. Browne ; Ben L. Feringa ; Saeed Amirjalayer ; Wybren Jan Buma ; Sander Woutersen ; Stephen R. Meech
• 刊名：Journal of Physical Chemistry A
• 出版年：2014
• 出版时间：August 7, 2014
• 年：2014
• 卷：118
• 期：31
• 页码：5961-5968
• 全文大小：403K
• ISSN：1520-5215

文摘

9,9鈥?Bifluorenylidene has been proposed as an alternative and flexible electron acceptor in organic photovoltaic cells. Here we characterize its excited state properties and photokinetics, combining ultrafast fluorescence and transient IR measurements with quantum chemical calculations. The fluorescence decay is ultrafast (sub-100 fs) and remarkably independent of viscosity. This suggests that large scale structure change is not the primary relaxation mode. The ultrafast decay populates a dark state characterized by distinct vibrational and electronic spectra. This state decays with a 6 ps time constant to a hot ground state that ultimately populates the initial state with a 20 ps time constant; these times are also insensitive to solvent viscosity. No metastable intermediate structures are resolved in the photocycle after population of the dark state. The implications of these results for the operation of 9,9鈥?bifluorenylidene as an electron acceptor and as a potential molecular switch are discussed.