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

Abstract

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 (A(Z) > A(X), A(Y)), while in nonbrominated Ga-corrole, the in-plane triplet sublevels are preferentially populated (A(X), A(Y) ≫ A(Z)). The differences in the photophysical properties of the corroles are attributed to the heavy atom effect upon corrole skeleton bromination, which enhances the spin-orbit coupling strength in the brominated complex, thus affecting its ISC and ZFS parameters.

Coordination chemistry of corroles with focus on main group elements

“…Addition of bromine to a benzene solution of 2a resulted in the fully brominated gallium(III) corrole Ga(tpfc-Br 8 )(py) 3 [40]. By adding the Vilsmeier reagent (POCl 3 in DMF) to CH 2 Cl 2 solution of 2a, two formylated gallium complexes were obtained (4a, 4b) [39].…”

“…Time-resolved electron paramagnetic resonance (TREPR) spectroscopy, combined with selective laser light excitation, is a suitable tool to provide unique information on the nature of corrole complexes bearing different core ions and different axial ligands [40]. The value and the sign of the zero-field splitting (ZFS) parameter D is an important feature of the corrole.…”

A Spectroscopic and Theoretical Investigation of a Free‐Base meso‐Trithienylcorrole

“…meso-Triaryl-substituted corroles were firstly described by Gross and co-workers in 1999 (11,12). Their syntheses were improved since (10,(13)(14)(15)(16), and numerous investigations illuminated the unique structural and electronic aspects of triarylcorroles (and their metal complexes) (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34). The smaller trianionic corrolato ligand has a greater ability to stabilize higher central metal oxidation states than the larger dianionic porphyrinato ligand (35)(36)(37).…”

Metallocorroles as Photocatalysts for Driving Endergonic Reactions, Exemplified by Bromide to Bromine Conversion

“…[5] Considering photocatalysis,p orphyrins come into mind since they are versatile photosensitizers and their photoexcited state is efficiently quenched by halides. [6] Based on some very encouraging features disclosed for metallocorroles in completely different light-driven applications, [7][8][9][10][11] we have decided to check if they may be used as photosensitizers that are able to catalyze the aerobic oxidation of bromide to bromine using only sunlight.…”

“…Based on the above,t he attention was driven to the previously synthesized Al-Br 8 [7a] and Ga-Br 8 [11] and to the analogous phosphorous corrole.T he latter was expected to have photophysical properties that are similar to Sb-Br 8 ,b ut of higher stability regarding demetalation. Treatment of H 3 (tpfc-Br 8 )b yP Cl 3 at RT and subsequent column chromatography allowed the isolation of the bis-hydroxophosphorus(V) corrole P-Br 8 in high yield.…”