Unveiling the Multifaceted Nature of 4-(4-MethylphenylThio)benzophenone: A Combined DFT, NBO, and Spectroscopic Investigation of its Electronic Structure and Excited States

Benzophenone and its derivatives play a crucial role as UV (ultra-violet) lters and UV-ink photoinitiators. The photoinitiating properties of benzophenones are primarily linked to the degree of -conjugation and the extent of delocalization within the molecule. Understanding the intricate interplay of conjugation, delocalization, and substituent effects allows for the precise customization of benzophenone derivatives to meet speci c application requirements. Quantum mechanical calculations, employing the B3LYP/6-311++G(d, p) density functional theory (DFT), are utilized to compute chemical reactivity, stability, and photoinitiating properties for 4-4 (methylphenylthio) benzophenone. Various parameters such as proton af nity, ionization energy, electron af nity, reactivity, and spectroscopic properties are determined. The DFT-computed infrared spectra align well with available experimental results. The UV/Visible spectra obtained using TD-DFT reveal absorption toward higher wavelengths, attributed to the extended delocalization of -electrons. In an aqueous medium, the absorption spectra of 4-4 (methylphenylthio) benzophenone exhibit a high- intensity peak with a longer wavelength shift in the visible region compared to gas-phase spectra. This knowledge provides the foundation for designing novel initiators with tailored light absorption, excited state lifetimes, and reaction selectivities. Consequently, these advancements open doors to bene ts in UV-curing, photopolymerization, and other light-driven processes.