Deep insight into the charge-transfer cocrystals: Decreasing structural overlap induced bathochromically shift emission

Two charge transfer (CT) cocrystals (cocrystal-O and cocrystal-R) were prepared by solvent evaporation method with 9-(3-(pyren-1-yl)phenyl)-9H-carbazole (1PY-mCzB) as donor (D), 1,2,4,5-tetracyanobenzene (TCNB) as acceptor (A). The spectroscopic studies, single-crystal X-ray diffraction structure and theoretical calculations are carried out to explore the relationship between structures and properties of cocrystal system. The results indicate both cocrystals were assembled as the … D-A-D … alternated stacking way, implying strong CT interactions. Cocrystal-O with larger structural overlap and smaller intermolecular distance shows orange fluorescence with λmax = 592 nm, while cocrystal-R with smaller structural overlap and larger intermolecular distance shows red fluorescence with λmax = 614 nm. Actually, the decreasing structural overlap plays a key role in bathochromically shift emission for cocrystal-R, and it make the higher CT excited transition proportions in cocrystal-R (92.74%) than that in cocrystal-O (89.96%). This work not only provides a deep insight into CT cocrystals, but also supplies some guidance for the design and preparation of multicomponent luminescent materials.