Solvent-dependent Photophysical Dynamics of Nitro-substituted Triphenylamine: Insights from Spectroscopies and DFT Calculations

Triphenylamine (TPA) derivatives, prized for their electron-donating and hole-transport properties, are pivotal in optoelectronic materials. However, the photophysical behavior of nitro-substituted variants remains underexplored despite their potential in triplet-mediated applications. Herein, we investigate the ground- and excited-state dynamics of 4-bromo-N-(4-bromophenyl)-N-(4-nitrophenyl)aniline (Br-NTPA), a nitro-substituted TPA, using Raman, UV-Vis absorption, fluorescence, and nanosecond transient absorption (ns-TA) spectroscopy across various solvents, experimently and therotically (DFT calculation). Raman spectra confirm the ground-state structure, while UV-Vis absorption reveals a solvent-sensitive charge transfer (CT) band at 377–394 nm, red-shifting 17 nm in acetonitrile versus cyclohexane. Fluorescence quantum yields drop from 0.211 in solid powder to <0.001 in acetonitrile, reflecting solvent-driven nonradiative decay, with ns-TA spectra identifying triplet states (T_CT and T_TICT) with quenching rates of 3.89 × 10⁹ –6.85 × 10⁹ (mol/L)⁻¹·s⁻¹, approaching diffusion limits. These results highlight solvent polarity’s role in modulating singlet and triplet CT character, with intersystem crossing and structural relaxation dictating outcomes. This integrated study elucidates Br-NTPA’s tunable photophysics, offering insights for designing efficient optoelectronic and photochemical materials.