Morphology-Dependent Luminescence and Optical Waveguide Property in Large-Size Organic Charge Transfer Cocrystals with Anisotropic Spatial Distribution of Transition Dipole Moment

Organic cocrystals exhibiting active optical waveguide behaviors are strongly related to the total internal reflection, molecule stacking modes, and the spatial distribution of transition dipole moment (mu) in crystals. However, organic charge transfer (CT) cocrystals as new materials that exhibit optical waveguide property responses to anisotropic spatial distribution of mu are still unknown. Herein, prepared is a novel organic CT cocrystal 9AC-TCNB (9AC = 9-anthracene carboxylic acid, TCNB = 1,2,4,5-tetracyanobenzene) with a mixed stacking structure of donor (D) and acceptor (A) along two different orientations on the same lattice plane. According to various spectroscopic analyses, two direction-oriented asymmetric light propagate in the cocrystal derived from the anisotropic spatial distribution of mu have been confirmed. Photoluminescence (PL) microscopic images and spatial resolution PL spectra of 1D and 2D 9AC-TCNB cocrystals further demonstrate that the CT cocrystals possess morphology and color-dependent optical waveguide properties with anisotropy, which confirms the principle theory of light propagation. This result can open new potential applications of organic cocrystals in large-scale optical waveguide devices and integrated optics.