Impact of C-H···X (X = F, N) and π-π Interactions on Tuning the Degree of Charge Transfer in F₆TNAP-Based Organic Binary Compound Single Crystals

Single crystals of four new charge transfer compounds, triphenylene (TP)-1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F₆TNAP), pyrene-F₆TNAP, phenanthrene (PA)-F₆TNAP, and naphtho[1,2-b:5,6-b']dithiophene (NDT)-F₆TNAP, with needle-like morphologies and dark color were grown by chemical vapor transport. The influence of C-H···X (X = F, N) interactions as well π-π interactions on the degree of charge transfer (DCT) in these compounds was investigated. The results indicate that the DCT is proportional to the interplanar D-A distance along the π-π interaction direction in TP-F₆TNAP, pyrene-F₆TNAP, and PA-F₆TNAP single crystals. With the decreasing of the D-A interplanar distance from 3.3560 Å of TP-F₆TNAP to 3.3254 Å of PA-F₆TNAP, the DCT is significantly increased from 0.03 ± 0.02 of TP-F₆TNAP to 0.26 ± 0.03 of PA-F₆TNAP, showing the strong relationship between π-π interactions and the DCT. In addition to π-π interactions, a stronger C-H···F interaction (C-H···F bond length: 2.3689 Å) is observed in NDT-F₆TNAP, which exhibits larger contributions to the DCT of NDT-F₆TNAP (0.46 ± 0.04). These results suggest that it is important to evaluate the DCT by considering the combination of π-π interactions and C-H···X (X = F, N) interactions in organic charge transfer compounds.