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



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


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.
Advanced Materials


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


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], (Accessed April 14, 2024)
Created September 13, 2016, Updated October 12, 2021