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Polymorphism in the 1:1 Charge-Transfer Complex DBTTF-TCNQ and Its Effects on Optical and Electronic Properties

Published

Author(s)

Katelyn Goetz, Jun?ya Tsutsumi, Sujitra J. Pookpanratana, Jihua Chen, Curt A. Richter, Christina A. Hacker, Tatsuo Hasegawa, Oana Jurchescu

Abstract

The organic charge-transfer (CT) complex dibenzotetrathiafulvalene – 7,7,8,8-tetracyanoquinodimethane (DBTTF-TCNQ) is found to crystallize in two polymorphs when grown by physical vapor transport: the known α-polymorph and a new structure, the β-polymorph. Structural and elemental analysis via selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), and polarized IR spectroscopy reveal that the complexes have the same stoichiometry with a 1:1 donor:acceptor ratio, but exhibit different unit cells. Though the structural differences are small, they result in significant differences in the optoelectronic properties of the crystals. Raman spectroscopy shows that the α-polymorph has a degree of charge transfer of about 0.5e while the β-polymorph is nearly neutral. Organic field-effect transistors fabricated on these crystals reveal that in the same device structure both polymorphs are ambipolar, but the α-polymorph exhibits electron-dominant transport while the β-polymorph is hole-dominant. Together, these measurements imply that the transport features result from differing donor-acceptor overlap and consequential varying in frontier molecular orbital mixing. These features have been suggested theoretically for charge-transfer complexes but have not explicitly confirmed by experiment until now.
Citation
Advanced Materials
Volume
2
Issue
10

Keywords

organic semiconductors, charge-transfer complexes, single crystals, polymorphism

Citation

Goetz, K. , Tsutsumi, J. , Pookpanratana, S. , Chen, J. , Richter, C. , Hacker, C. , Hasegawa, T. and Jurchescu, O. (2016), Polymorphism in the 1:1 Charge-Transfer Complex DBTTF-TCNQ and Its Effects on Optical and Electronic Properties, Advanced Materials, [online], https://doi.org/10.1002/aelm.201600203 (Accessed September 17, 2021)
Created September 14, 2016, Updated November 10, 2018