Excited-state torsional relaxation dynamics of meso–meso directly linked corrole dimers: importance of linking position

Abstract

Herein, we present a combined spectroscopic and computational study on 5,5′-linked and 10,10′-linked corrole dimers, 5CD and 10CD, respectively, to reveal their strikingly different excited-state dynamics. The excited-state dynamics of 10CD indicate relatively small electronic interactions between the two corrole units, which is similar to the case of the meso–meso directly linked Zn(II) porphyrin dimer. On the other hand, 5CD exhibits characteristic excitation-wavelength-dependent dual fluorescence. Transient absorption spectra of 10CD on the picosecond timescale showed torsional relaxation with a time constant of 25 ps, whereas the torsional relaxation of 5CD was faster, exhibiting a time constant of 10 ps. Quantum calculations have indicated that the eccentric dual fluorescence and the faster torsional relaxation process of 5CD are consequences of a large π-orbital coefficient at the connecting 5-position, which enhances the conjugative stabilization in the excited-state. In contrast, a small π-orbital coefficient at the 10-position and a larger torsional barrier of 10CD cause monomer-like characters in the excited-state.