Solvent Effects on the Phosphorescence of Gold(III) Complexes Chelated by ß-Multisubstituted Corroles.

A set of gold corrole complexes containing four different ß-substituent groups (Br/I/CF3), namely, 4Br-Au, 4I-Au, and 4CF3-Au, were investigated; all showed room temperature phosphorescence. The phosphorescence quantum yields of the corroles were determined using tetraphenylporphyrin as a reference: Φph (4I-Au, 0.75%) > Φph (4Br-Au, 0.64%) > Φph (4CF3-Au, 0.38%). 4CF3-Au exhibited near-IR emission (858 nm, aerobic); absorbance intensity for the Q-band was higher than that for the Soret band. Complex 4I-Au showed a longer phosphorescence lifetime (82 µs) compared to those of 4Br-Au (53 µs) and 4CF3-Au (28 µs; N2, tol). Thermally activated delayed fluorescence (TADF) emission of 4I/Br-Au complexes was observed: stronger emission intensity correlated with increasing temperature. Good negative correlations for 4I/Br-Au were observed between the Soret band absorption energy and the solvent polarizability: excited states of 4I/Br-Au are more polar than their ground states. TD-DFT calculations revealed very fast intersystem crossing (ISC) rate constants, 2.20 × 1012 s-1 (4CF3-Au) > 1.96 × 1011 s-1 (4Br-Au) > 1.15 × 1011 s-1 (4I-Au), and importantly, the reverse intersystem crossing (rISC) rate constants are determined as 1.68 × 107 s-1 (4I-Au) > 2.40 × 103 s-1 (4Br-Au) ≫ 8.09 × 10-8 s-1 (4CF3-Au). The exceptionally low rISC rate constant of 4CF3-Au is attributed to its more steric and deformed structure bearing a larger energy gap between the S1 and T1 states.

Effect of Selective CF3 Substitution on the Physical and Chemical Properties of Gold Corroles.

Gold corroles are not readily accessible and they display no interesting physical or chemical properties. A facile methodology has now been developed for obtaining selectively CF3 -substituted gold(III) corroles and the introduction of these groups has been found to have an immense effect on the structures of the complexes, their photophysical and redox properties, and on their ability to participate in catalytic processes.

Trifluoromethylation for affecting the structural, electronic and redox properties of cobalt corroles.

Cobalt corroles excel as catalysts in the two most clean-energy-relevant processes, the electrochemical oxygen reduction reaction (ORR) and the hydrogen evolution reaction (HER). Common to both is the need to replace platinum by earth abundant metal ions and the desire to positively shift the redox potentials of the catalysts. The main aim of this study was to prepare cobalt corroles whose macrocyclic skeleton contains trifluoromethyl groups, since they are purely electron withdrawing with no π-back donation capability. New synthetic methodologies were developed for gaining access to a series of cobalt(iii) corroles with two, three, and four CF3 groups and all of them were fully characterized for determining the effect of the CF3 groups on the structural parameters, electronic structures and redox processes. Our most novel findings are the ability to control the number and positioning of the CF3 groups, the macrocycle deformation and the quite dramatic changes in the electronic spectra induced thereby, the isolation of 4-coordinate cobalt(iii) corroles and the paramagnetic NMR spectra of these intermediate-spin complexes, and the 180 mV/CF3 shift of redox potentials in the direction desired for the utility of the complexes as electrocatalysts.

One-Pot Conversion of Fluorophores to Phosphorophores.

Facile, one-pot conversion of free base 5,10,15-tris(pentafluorophenyl)corrole, (H3)tpfc, into the coinage metal complexes of 2,3,17,18-tetraiodo-5,10,15-tris(pentafluorophenyl)corrole, (I4-tpfc)M (M = Cu, Ag, Au), is reported. The iodination/metalation procedures provide much higher yields and larger selectivity than both conceivable stepwise syntheses. Photophysical analysis shows that the gold(III) complex (I4-tpfc)Au displays phosphorescence at room temperature and a substantial quantum yield for singlet oxygen formation.

Ultrafast Photoinduced Charge Separation Leading to High-Energy Radical Ion-Pairs in Directly Linked Corrole-C60 and Triphenylamine-Corrole-C60 Donor-Acceptor Conjugates.

Closely positioned donor-acceptor pairs facilitate electron- and energy-transfer events, relevant to light energy conversion. Here, a triad system TPACor-C60 , possessing a free-base corrole as central unit that linked the energy donor triphenylamine (TPA) at the meso position and an electron acceptor fullerene (C60) at the ß-pyrrole position was newly synthesized, as were the component dyads TPA-Cor and Cor-C60. Spectroscopic, electrochemical, and DFT studies confirmed the molecular integrity and existence of a moderate level of intramolecular interactions between the components. Steady-state fluorescence studies showed efficient energy transfer from (1) TPA* to the corrole and subsequent electron transfer from (1) corrole* to fullerene. Further studies involving femtosecond and nanosecond laser flash photolysis confirmed electron transfer to be the quenching mechanism of corrole emission, in which the electron-transfer products, the corrole radical cation (Cor(⋅+) in Cor-C60 and TPA-Cor(⋅+) in TPACor-C60) and fullerene radical anion (C60(⋅-)), could be spectrally characterized. Owing to the close proximity of the donor and acceptor entities in the dyad and triad, the rate of charge separation, kCS , was found to be about 10(11)  s(-1), suggesting the occurrence of an ultrafast charge-separation process. Interestingly, although an order of magnitude slower than kCS , the rate of charge recombination, kCR , was also found to be rapid (kCR ≈10(10)  s(-1)), and both processes followed the solvent polarity trend DMF>benzonitrile>THF>toluene. The charge-separated species relaxed directly to the ground state in polar solvents while in toluene, formation of (3) corrole* was observed, thus implying that the energy of the charge-separated state in a nonpolar solvent is higher than the energy of (3) corrole* being about 1.52 eV. That is, ultrafast formation of a high-energy charge-separated state in toluene has been achieved in these closely spaced corrole-fullerene donor-acceptor conjugates.