P-Centered Dibenzophospholyl Radical: A Matrix Isolation IR, UV/Vis and ESR Spectroscopic Study

Organophosphorus compounds are fundamental building blocks in organic synthesis, pharmaceuticals, and most notably as optoelectronic materials. In this study, we describe the generation and matrix isolation of a dibenzophosphole-based P-centered radical via photolysis or pyrolysis from an iodo precursor in Ar, and para-hydrogen (p-H₂). The radical is experimentally characterized by infrared (IR), UV/Vis and electron spin resonance (ESR) spectroscopy. Based on a detailed analysis of the spectroscopic data, supported by quantum chemical calculations, the P-dibenzophospholyl radical is a π-radical with a ²B₁ electronic ground state, where the unpaired electron resides in a p-orbital perpendicular to the molecular plane and with some degree of electron density delocalization over the aromatic rings. We compared the experimental and computational results of the P-dibenzophospholyl radical with its nitrogen analogue, the N-carbazolyl radical, which is a highly delocalized π-radical.