Solvation-Enhanced Intermolecular Charge Transfer Interaction in Organic Cocrystals: Enlarged C-C Surface Close Contact in Mixed Packing between PTZ and TCNB.

The mixed π-π packing of the donor (D) and acceptor (A) molecules is the highlighting feature of the intermolecular interactions following charge transfer (CT) issues in organic cocrystal systems. There is an inverse relationship between the D-A interplanar distance and the intermolecular CT interaction. However, the D-A C-C surface close contact (relative areas) on the intermolecular CT interactions in organic cocrystal systems is rarely investigated. Herein, we designed and constructed a novel cocrystal and its solvate cocrystal. The structural and electrostatic potential analyses suggest that the solvation destroys the N-H···N hydrogen bond interaction between phenothiazine (PTZ) and 1,2,4,5-tetracyanobenzene (TCNB), which causes the TCNB molecules to have a 90° rotation along the normal axis of the PTZ plane. Thus, the D-A C-C surface close contact is enlarged, strengthening the intermolecular π-π stacking interactions and intermolecular CT interaction between PTZ and TCNB, which are further evidenced by the absorption and Raman spectroscopic analyses. This study provides rare evidence of the enlarged C-C surface close contact in the mixed packing between D and A that greatly contributes to the intermolecular CT interaction in a D-A cocrystal system. It also provides a deeper understanding of the role of solvation in the structure-property relationship of organic cocrystal materials.