Photophysical Properties of a Rhodium Tetraphenylporphyrin-tin Corrole Dyad. The First Example of a Through Metal–Metal Bond Energy Transfer†

Abstract

The luminescence spectroscopy study and the determination of the photophysical parameters for the M-M'-bonded rhodium meso-tetraphenylporphyrin-tin(2,3,7,13,17,18-hexamethyl-8,12-diethylcorrole) complex, (TPP)Rh-Sn(Me6Et2Cor) 1, was investigated. The emission bands as well as the lifetimes (tau(e)) and the quantum yields (Phi(e); at 77 K using 2MeTHF as solvent) were compared with those of (TPP)RhI 2 (TPP = tetraphenylporphyrin) and (Me6Et2Cor)SnCl 3 (Me6Et2Cor = 2,3,7,13,17,18-hexamethyl-8,12-diethylcorrole) which are the two chemical precursors of 1. The energy diagram has been established from the absorption, fluorescence and phosphorescence spectra. The Rh(TPP) and Sn(Me6Et2Cor) chromophores are the energy donor (D) and acceptor (A), respectively. The total absence of fluorescence in 1 (while fluorescence is observed in the tin derivative 3) indicates efficient excited state deactivation, presumably due to heavy atom effect and intramolecular energy transfer (ET). The large decreases in tau(P) and Phi(P) of the Rh(TPP) chromophore going from 2 to 1 indicate a significant intramolecular ET in the triplet states of 1 with an estimated rate ranging between 10(6) and 10(8) s(-1). Based on the comparison of transfer rates with other related dyads that exhibit similar D-A separations and no M-M' bond, and for which slower through space ET processes (10(2)-10(3) s(-1)) operate, a through M-M' bond ET has been unambiguously assigned to 1.

New rhodium(I) supramolecular structures containing pyridyl and bipyridyl ligands

“…However, other metals have also been used in these reactions. In particular, Rh(I) and Ir(I) units have been explored in the synthesis of bi- [23][24][25][26][27] and three-dimensional compounds [28,29] and they are of great interest due to their potential catalytic activity and luminescent behaviour, that could be very useful in host-guest studies [30][31][32][33][34][35].…”

What can we learn from artificial special pairs?

“…For curiosity purposes, the use of a metal−metal bond holding the two chromophores together was also investigated. 14,15 In these cases, rigidity was clearly not an issue keeping a clear cofacial geometry with an extremely short interplanar distance, but the expected and unavoidable heavy atom effect was clearly present. Such an approach is also not practical for such an endeavour.…”

Comments on the through-space singlet energy transfers and energy migration (exciton) in the light harvesting systems

“…Over the past 7 years, our research groups investigated a large series of cofacial bisporphyrin dyads along with the corresponding homo-bimetallic models [23][24][25][26][27][28][29][30][31][32][33][34][35]. Most of these compounds were especially designed for through space singlet-singlet (S 1 ) and triplet-triplet (T 1 ) energy transfer (ET) investigations (Scheme 1) [23][24][25][26][27][28][29][30][31][32][33][34][35].…”

“…Most of these compounds were especially designed for through space singlet-singlet (S 1 ) and triplet-triplet (T 1 ) energy transfer (ET) investigations (Scheme 1) [23][24][25][26][27][28][29][30][31][32][33][34][35]. Rate for S 1 ET (S 1 k ET ) turned out to be much slower than that found for LH I and LH II.…”