Insight into Intermolecular Charge Transfer Determined by Two Packing Mode Cocrystals

Abstract

Cocrystal molecules obtained through simple self-assembly of small organic molecules often have unique properties that monomolecular crystals do not have. However, it is not easy to purposefully construct a series of cocrystals with specific functions. Moreover, the structures and dynamics of cocrystals are still riddles on account of the initial stage of cocrystal development. In this work, two electron donors (hexamethylbenzene and 1,3,5-trimethoxybenzene) are selected to govern the degree of charge transfer (CT) between the donor and acceptor (pyromellitic dianhydride), which may help obtain two light-emitting materials. In comparison with the monocomponent crystals, the emitting wavelengths of these cocrystals redshift from the ultraviolet range to visible region. It is worth noting that the intermolecular CT of these cocrystal materials is probed by femtosecond transient absorption (fs-TA) spectrometry. The relationship between the characteristics of emission and the stacking patterns of two specific cocrystals has been explored by fs-TA and density functional theory simulation. This work established the foundation to trace the excited-state evolution channels of the organic cocrystal materials.