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Issue 31, 2019
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Ground-state charge-transfer interactions in donor:acceptor pairs of organic semiconductors – a spectroscopic study of two representative systems

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Abstract

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 (F6TCNNQ) using Polarization-Modulation Infrared Reflection-Absorption Spectroscopy (PMIRRAS). For DIP:F6TCNNQ 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 F6TCNNQ in the different mixtures with DIP, we quantify the average ground-state charge-transfer (GS-CT) to be ρavg = (0.84 ± 0.04) e. The PMIRRAS data for P3HT:F6TCNNQ 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 F6TCNNQ in the mixtures with DIP and P3HT, respectively, and support it with DFT calculations for the isolated F6TCNNQ. Such comparison allows to identify the vibrational signatures of the acceptor mono-anion in P3HT:F6TCNNQ, 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 F6TCNNQ, or similar quinoid systems, for a reliable picture of the nature of GS-CT interactions.

Graphical abstract: Ground-state charge-transfer interactions in donor:acceptor pairs of organic semiconductors – a spectroscopic study of two representative systems

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Publication details

The article was received on 24 May 2019, accepted on 23 Jul 2019 and first published on 23 Jul 2019


Article type: Paper
DOI: 10.1039/C9CP02939G
Phys. Chem. Chem. Phys., 2019,21, 17190-17199

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    Ground-state charge-transfer interactions in donor:acceptor pairs of organic semiconductors – a spectroscopic study of two representative systems

    G. Duva, P. Beyer, R. Scholz, V. Belova, A. Opitz, A. Hinderhofer, A. Gerlach and F. Schreiber, Phys. Chem. Chem. Phys., 2019, 21, 17190
    DOI: 10.1039/C9CP02939G

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