Photoaccelerated Hole Transfer in Oligothiophene Assemblies

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• 作者：Chao Lu ; Mamoru FujitsukaTetsuro Majima
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：January 12, 2017
• 年：2017
• 卷：121
• 期：1
• 页码：649-655
• 全文大小：507K
• ISSN：1932-7455

文摘

A new series of mesitylene-linked oligothiophenes (nT, n is the number of thiophene units), including 2T-M, 3T-M, 4T-M, 4T-M-2T, and 4T-M-3T, was prepared to investigate the intramolecular hole transfer (HT) from the excited radical cation for the first time. The results of spectroscopic and theoretical studies indicated that mesitylene acts as a spacer minimizing the perturbation to the thiophene π-conjugation and increasing the stability of nT radical cations (nT^•+). Femtosecond laser flash photolysis was applied to the FeCl₃-oxidized 4T^•+-M, 4T^•+-M-2T, and 4T^•+-M-3T. Upon 670 nm laser excitation, the transient absorption spectra of 4T^•+-M showed the existence of two species as the D₁ and D₀^hot states. The intramolecular HT processes from excited 4T^•+ with the time constants of 1.6 and 0.8 ps were observed upon excitation of 4T^•+-M-2T and 4T^•+-M-3T, respectively. This is the first capture of such ultrafast processes with the subsequent back HT from the ground-state 2T^•+ or 3T^•+ in nT assemblies. The current findings indicated an accelerated migration of photocarriers (polarons) in thiophene-based p-type semiconductor materials upon irradiation and provided a fresh viewpoint to understand the successive HT in polythiophenes for various organic molecular devices.