Modulation of luminescence properties of cocrystals composed of amino substituted dimethyl phthalates and 1,2,4,5-tetracyanobenzene by crystal engineering

Abstract

The preparation of a cocrystal is one of the effective strategies to tune the luminescence properties of organic crystals. In this work, four charge transfer cocrystals were constructed with isomeric substances of amino substituted dimethyl phthalates as the donors and 1,2,4,5-tetracyanobenzene as the acceptor. The emission range of the individual electron donors is from 400 nm to 505 nm, while all cocrystals have their emission redshift exceeding 100 nm. The tunable emission range of the charge transfer cocrystals is from 573 nm to 640 nm. All the obtained four cocrystals contain π–π stacking structures with the presence of π–π and C–H⋯π interactions. Fourier transform infrared spectroscopy and UV-vis spectroscopy demonstrated the presence of charge transfer interactions in the cocrystals. The tuning of the luminescence properties of the cocrystals was explained by the analysis of the crystal packing structure and the intermolecular interaction, and the distribution of frontier orbitals was obtained by DFT calculation. We believe our work is helpful to understand the relationship between the crystal structure and luminescence properties in the charge transfer cocrystals and provide guidance for the modulation of the luminescence properties.