Tetraphenylethylene-thiazole derivatives: a combined experimental and DFT study for the rational design of novel...

A series of six novel tetraphenylethylene (TPE)-based derivatives with an NH1,3-thiazole linker and donor or acceptor substituents were synthesized and comprehensively investigated to elucidate structure-photophysical property relationships in solution and in the solid state. All compounds exhibited good thermal stability (5% weight loss above 211 °C) and irreversible oxidation processes, with frontier molecular orbitals predominantly localized on the TPENH1,3-thiazole fragment. Steady-state absorption and emission spectroscopy studies in five solvents with different polarity and at low temperature in an ethanol:methanol mixture revealed pronounced solvent, temperature and rotation effects on the radiative and non-radiative emission pathways. Low quantum yields were observed in solutions, with significantly higher quantum yields in the solid state. Furthermore, host-guest systems based on selected materials dispersed in polymer matrices were evaluated, revealing the highest quantum yield in poly(methyl methacrylate) (PMMA), polyvinylpyrrolidone (PVP), and polystyrene (PS). Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations supported the experimental findings, providing insight into frontier molecular orbitals and excited-state characteristics. Analysis based on Marcus theory calculations suggested potentially favorable charge-transport characteristics, particularly for the nitro-substituted derivative, which exhibited low and well-balanced hole and electron reorganization energies. The combined spectroscopic and theoretical analysis demonstrates that subtle structural modifications significantly modulate excited-state deactivation pathways and solid-state emission, providing valuable insight into the design of future luminescent organic materials.