Photoexcited Triplet State Properties of Brominated and Nonbrominated Ga(III)-Corroles as Studied by Time-Resolved Electron Paramagnetic Resonance†

The effect of the corrole macrocycle bromination on its photoexcited triplet state parameters was examined in a comparison study of brominated and nonbrominated Ga(III) 5,10,15-tris(pentafluorophenyl)corroles, employing X-band (9.5 GHz) time-resolved electron paramagnetic resonance (TREPR) spectroscopy. It is demonstrated that the spectrum of the brominated Ga-corrole is characterized by an opposite polarization pattern and a larger zero-field splitting (ZFS) parameter |D|, compared to nonbrominated Ga-corrole. With the assignment of a negative sign for the ZFS parameter D, the dominant intersystem crossing (ISC) pathways are evaluated. Spectral line shape analysis reveals that in the brominated Ga-corrole,the out-of-plane triplet sublevel is overpopulated (AZ > AX, AY), while in nonbrominated Ga-corrole, the in-plane triplet sublevels are preferentially populated (AX, AY ≫ AZ). The differences in the photophysical properties of the corroles are attributed to the heavy atom effect upon corrole skeleton br...