Charge-Transfer Transitions Govern the Reactivity and Photophysics of Vicinally Diphosphanyl-Substituted Diborapentacenes.

Abstract

2,3-Difluoro-5,14-dihydro-5,14-diborapentacene (DBP) was endowed with two vicinal Ph2 P groups by an SN Ar reaction at both CF sites using Ph2 PSiMe3 . Computations reveal the ambipolar product P to undergo P-to-B charge transfer under ambient light irradiation. Consequently, P is prone to photooxidation by air, yielding the Ph2 P(O) species PO. With S8 or [Me3 O][BF4 ], P furnishes the Ph2 P(S) or Ph2 P(Me)+ derivatives PS or [PMe][BF4 ]2 . Along the series P, PO, PS, and [PMe][BF4 ]2 , the redox potentials shift anodically from E1/2 =-1.89 V to -1.02 V (CH2 Cl2 ). Thus, derivatization of the Ph2 P group allows late-stage modulation of the LUMO-energy level of the DBP. Derivatization also influences the emission properties of the compounds, as PO shows green (521 nm) and [PMe][BF4 ]2 red (622 nm) fluorescence in C6 H6 , while P and PS are dark. With CuBr and AgBr, P forms dimeric [M(μ-Br)]2 complexes [PCu]2 and [PAg]2 , which show pronounced metal-to-ligand charge transfer (MLCT), making P a promising ligand for photocatalysts.