Tert-Butylcarbazole and Methoxycarbazole Substituted on the Phenazine Group Exhibit Mechano and Thermoresponsivity for TADF LEECs

Abstract

Two new well-defined donor–acceptor–donor (D–A–D′) thermally activated delayed fluorescence (TADF) molecules with mechanochromic and thermochromic architectures were designed and synthesized based on tert-butylcarbazole and methoxycarbazole substituents attached to a phenazine derivative. Density functional theory (DFT) studies revealed molecular structures with extended π-conjugation and low singlet–triplet energy gaps (ΔE_ST), which enhance reverse intersystem crossing (RISC) for efficient TADF. Single-crystal X-ray diffraction confirms differences in molecular packing. The dye composed of tert-butylcarbazole exhibits lower aggregation and higher photoluminescence quantum yield (PLQY) upon spin-coating in a solid film, owing to its bulkier structure. Thermal stability studies demonstrated high decomposition temperatures (T_d > 300 °C) and improved rigidity of the dye consisting of tert-butylcarbazole. Photophysical investigations revealed that the dyes dispersed in a tetrahydrofuran (THF):water mixture showed aggregation-induced emission enhancement (AIEE). Incorporation of the complex organometallic [Ir(buoppy)₂(dmapzpy)]PF₆ as a host in LEECs favors the energy transfer and yields single emission peaks at 588 and 587 nm with 60 wt % host content. The improved device attains maximum current (28.97 cd A^–1), power (22.11 lm W^–1), and external quantum efficiency (4.02%). These findings underline the significance of substituent design and host:guest interactions in improving TADF LEEC performance and provide new insights for high-efficiency optoelectronic devices.