Preparation, Thermal, and Optical Properties of D-A-Type Molecules Based on 1,3,5-Triazine for Violet-Blue Fluorescent Materials

Organic violet-blue fluorescent materials have garnered significant interest for a broad spectrum of applications. A series of triazine-based molecules, that is, 2,4,6-tri(9H-carbazol-9-yl)-1,3,5-triazine (TCZT), 2,4,6-tri(1H-indol-1-yl)-1,3,5-triazine (TIDT), and 2,4,6-tris(3,6-di-tert-butyl-9H-carbazol-9-yl)-1,3,5-triazine (TDBCZT), exhibiting violet-blue emission were synthesized via a catalyst-free aromatic nucleophilic substitution reaction. These compounds possess a non-planar and twisted structure with favorable charge-transfer characteristics, demonstrating excellent thermal stability (decomposition temperatures of 370 °C, 384 °C, and 230 °C, respectively). Cyclic voltammetry analysis, combined with time-dependent density functional theory (TD-DFT) calculations at the B3LYP/6-31G(d) level, offered detailed insights into their electronic structures and electrochemical properties. Optical properties were systematically characterized using Ultraviolet-visible (UV-Vis) absorption and photoluminescence (PL) spectroscopy. The compounds exhibited violet-blue luminescence with emission peaks located at 397 nm, 383 nm, and 402 nm in toluene, respectively. In their respective films, the compounds exhibited varying degrees of spectral shifts, with emission peaks at 408 nm, 381 nm, and 369 nm. Moreover, the CIE (Commission Internationale de l'Éclairage) coordinates of TIDT in toluene were (0.155, 0.067), indicative of excellent violet purity. These compounds demonstrated significant two-photon absorption (TPA) properties, with cross-sections of 4.6 GM, 15.3 GM, and 7.4 GM, respectively. Notably, they exhibited large molar absorptivities and substantial photoluminescence quantum yields (PLQYs), suggesting their potential for practical applications as violet-blue fluorescent materials.