Exploring the dynamic behaviour and optical properties of indolocarbazole charge-transfer cocrystals

Abstract

Organic charge-transfer cocrystals offer a well-established route to engineer crystalline materials by strategically selecting their coformers. Herein, we report two novel cocrystals with indolo[3,2,1-jk]carbazole as a donor molecule with two different components: 7,7,8,8-tetracyanoquinodimethane (ICZ-TCNQ) and tetrafluoro-1,4-benzoquinone (ICZ-TFBQ). The degree of charge transfer (DCT) was elucidated in both cocrystals through the use of FTIR and diffuse reflectance spectroscopic studies. The ICZ-TCNQ cocrystal shows photothermal conversion properties with an efficiency of 12.8 ± 2.1% at 0.52 W cm⁻². Moreover, the ICZ-TFBQ cocrystal shows thermally-driven rotational motions of the TFBQ fragment, reaching hundreds of MHz at ca. 348 K, as evidenced by ¹⁹F T₁ relaxation measurements and ¹³C CPMAS solid-state NMR experiments. Contrasting ICZ-TCNQ and ICZ-TFBQ cocrystals, our study offers a broad perspective on the structural and functional versatility of ICZ-based systems, providing deeper comprehension into their optical and dynamic behaviour.