Duva Giuliano, Beyer Paul, Scholz Reinhard, Belova Valentina, Opitz Andreas, Hinderhofer Alexander, Gerlach Alexander, Schreiber Frank
University of Tübingen, Institute for Applied Physics, Auf der Morgenstelle 10, 72076 Tübingen, Germany.
Humboldt-Universität zu Berlin, Department of Physics, Newtonstraße 15, 12489 Berlin, Germany.
Phys Chem Chem Phys. 2019 Aug 21;21(31):17190-17199. doi: 10.1039/c9cp02939g. Epub 2019 Jul 31.
We investigate blended donor:acceptor (D:A) thin films of the two donors diindenoperylene (DIP) and poly(3-hexylthiophene) (P3HT) mixed with the strong acceptor 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (FTCNNQ) using Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PMIRRAS). For DIP:FTCNNQ thin films we first carry out a comprehensive study of the structure as a function of the D : A mixing ratio, which guides the analysis of the PMIRRAS spectra. In particular, from the red-shift of the nitrile (C[triple bond, length as m-dash]N) stretching of FTCNNQ in the different mixtures with DIP, we quantify the average ground-state charge-transfer (GS-CT) to be ρ = (0.84 ± 0.04) e. The PMIRRAS data for P3HT:FTCNNQ blended films reveal nearly the same shift of the CT-affected C[triple bond, length as m-dash]N stretching peak for this system. This points towards a very similar CT strength for the two systems. We extend the analysis to the relative intensity of the C[triple bond, length as m-dash]N to the C[double bond, length as m-dash]C stretching modes of FTCNNQ in the mixtures with DIP and P3HT, respectively, and support it with DFT calculations for the isolated FTCNNQ. Such comparison allows to identify the vibrational signatures of the acceptor mono-anion in P3HT:FTCNNQ, thus indicating a much stronger, integer CT-type interactions for this system, in agreement with available optical spectroscopy data. Our findings stress the importance of a simultaneous analysis of C[triple bond, length as m-dash]N and C[double bond, length as m-dash]C stretching vibrations in FTCNNQ, or similar quinoid systems, for a reliable picture of the nature of GS-CT interactions.
我们使用偏振调制红外反射吸收光谱法（PMIRRAS）研究了两种给体二茚并苝（DIP）和聚（3-己基噻吩）（P3HT）与强受体1,3,4,5,7,8-六氟四氰基萘并二甲基苯醌（FTCNNQ）混合而成的给体：受体（D:A）混合薄膜。对于DIP:FTCNNQ混合薄膜，我们首先对其结构作为D:A混合比例的函数进行了全面研究，这为PMIRRAS光谱的分析提供了指导。特别是，通过FTCNNQ在与DIP的不同混合物中腈基（C≡N）伸缩振动的红移，我们将平均基态电荷转移（GS-CT）量化为ρ = (0.84 ± 0.04) e。P3HT:FTCNNQ混合薄膜的PMIRRAS数据显示，该体系中受CT影响的C≡N伸缩峰的位移几乎相同。这表明这两个体系的CT强度非常相似。我们将分析扩展到FTCNNQ在与DIP和P3HT的混合物中C≡N与C═C伸缩模式的相对强度，并通过对孤立的FTCNNQ进行密度泛函理论（DFT）计算来支持这一分析。这种比较有助于识别P3HT:FTCNNQ中受体单阴离子的振动特征，从而表明该体系存在更强的整数CT型相互作用，这与现有的光谱数据一致。我们的研究结果强调了同时分析FTCNNQ或类似醌类体系中C≡N和C═C伸缩振动对于可靠了解GS-CT相互作用本质的重要性。
