Charge-transfer cocrystal engineering of anthracene chalcone compound containing cyano group: DFT-guided modulation of solid-state optical properties

Abstract

The charge transfer (CT) cocrystal A4BTC of anthracene chalcone compound (αZ)-α-(9-Anthracenylmethylene)-4-pyridineacetonitrile (A4BCN) with 1,2,4,5-Benzenetetracarbonitrile (TCNB) was successfully constructed by supramolecular self-assembly technology. The cocrystal was formed based on π^…π interactions in the D^…A^…D mode was stacked in the solid state. The A4BCN acted as a donor (D) and the electron-deficient TCNB acted as an acceptor (A). The pure phase formation of the cocrystal was confirmed by PXRD and FT-IR analysis. Solid-state optical properties revealed that, in comparison with the donor, A4BTC exhibited a red-shifted UV absorption band of 75 nm and a 73 nm red-shifted fluorescence emission peak. Moreover, the emission quantum yield and fluorescence lifetime showed a remarkable increase. Specifically, the quantum yield was enhanced by a factor of 4.47, and the fluorescence lifetime was extended by 6.9 ns, significantly improving the fluorescence performance. Using Density Functional Theory, the weak intermolecular and π^…π interactions in A4BTC were analyzed based on the obtained SXRD crystal data, confirming the CT effect. It could also be inferred that the narrowing of the cocrystal's bandgap due to the CT effect induced a change in the transition dipole moment of the excited state. The change in the excited state dipole moment was directly correlated with the optical properties, thereby achieving the modulation of the optical properties. This study integrated theoretical calculations and experimental investigations, not only clarifying the mechanism by which π^…π stacking-mediated CT effect modulates optical properties, but also establishing a theoretical model for the development of high-performance tunable organic fluorescent materials.