Theoretical investigation of Norrish type I photoinitiator
diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO)
DOI:
https://doi.org/10.26512/2446-564X2026e61681Keywords:
DFT; TPO; dental resin; photoinitiators; TD-DFT; electronic propertiesAbstract
Diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO) is widely used as a Norrish Type I photoinitiator in dental resins due to its high efficiency in generating free radicals under UV irradiation. In this work, a theoretical investigation based on Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) was carried out to analyze the structural, electronic, and spectroscopic properties of TPO. The geometries of the ground state (S0), singlet excited state (S1), and triplet state (T1)) were optimized at the B3LYP/6-31+G(d) level. Structural analysis revealed significant elongation of the C–P bond and the carbonyl group in the excited states, indicating electronic weakening associated with photochemical cleavage. Mulliken charge and spin density analyses showed that electronic redistribution is strongly localized in the acylphosphine oxide fragment, particularly in the triplet state. The simulated UV - Vis spectrum exhibits an intense absorption band in the UV region with a maximum at 375 nm, in agreement with experimental reports. The calculated HOMO - LUMO gap (3.891 eV) is consistent with the observed transition energy. These findings provide theoretical support for the Norrish Type I cleavage mechanism and highlight the importance of computational modeling for understanding photoinitiators used in restorative dentistry.
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