Impact of C-H center dot center dot center dot X (X = F, N) and pi-pi Interactions on Tuning the Degree of Charge Transfer in F(6)TNAP-Based Organic Binary Compound Single Crystals

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