Unprecedented optically induced long-lived intramolecular electron transfer in cobalt–dioxolene complexes

Abstract

The observation of very long lifetimes of the metastable states of two cobalt-dioxolene complexes undergoing photoinduced and high T(c) thermally-induced valence tautomer interconversion opens new research perspectives.

Complete Direct and Reverse Optically Induced Valence Tautomeric Interconversion in a Cobalt–Dioxolene Complex

“…This confirms the major role of the intermolecular interactions and crystal packing in determining the relative stability of the different charge distributions in valence tautomeric complexes. [17,18] The presence of two distinct Co centers in the lattice is confirmed by the solution of X-ray structures at 100 and 160 K (Figure 2), even if we could only obtain a partial refinement [25] due to the probable formation of spin-like domains. [26] Notwithstanding these limitations, we can safely conclude that at both temperatures the asymmetric unit consists of two crystallographically independent [CoA C H T U N G T R E N N U N G (Me 2 tpa)-…”

“…[20][21][22][23] For this reason we decided to synthesize different 6 ) complex (1, DBCat = 3,5-di-tert-butylcatecolato) which was observed to undergo both entropy driven and optically induced valence tautomerism. The results we obtained for the toluene solvate provide, when compared to those previously reported for other derivatives, [17,18] an intriguing benchmark for the description of these systems.…”

“…1 mW cm À2 ), the system evolves to the metastable highspin state, according to the valence tautomeric interconversion, Co + [18] not undergoing VT, the steady-state conversion has been estimated to 85 % of the total molar amount of cobalt after irradiation. Such a high percentage of conversion, compared with the ethanol solvate, [17,18] may be attributed to the increase of the lattice volume per molecule (3863 3 at 100 K for the toluene solvate vs 3799 3 at 150 K for the ethanol solvate). This may account by itself for the improved conversion capabilities of the cation, by reducing the lattice pressure.…”

“…[15][16][17][18][19] In recent publications we have shown how the charge distribution of a series of cobalt-dioxolene complexes of for- 6 ) (Me n tpa = methyl derivatives of tris(2-pyridylmethyl)amine, diox = catecholato (Cat) or semiquinonato (SQ) forms of o-quinones) can be qualitatively related to the difference between the redox potentials of the metal acceptor and of the coordinated dioxolene ligand, which can be independently observed in a series of appropriate reference compounds. [17,18] This allowed us to justify the observation of entropy driven valence tautomeric interconversion for some of these complexes as well as the trend of the relaxation decay rates of the optically induced metastable redox isomers at cryogenic temperatures. The observed data showed that the intramolecular ET process in these 1:1 adducts were, as expected, extremely sensitive to lattice energies.…”

Tuning the Charge Distribution and Photoswitchable Properties of Cobalt–Dioxolene Complexes by Using Molecular Techniques

“…A preliminary account of some of the experimental results reported herein has recently been published. [45] Results Synthesis: The four Me n tpa ligands were prepared by using a general one-step procedure, according to the recently reported preparation of tpa. [46] Treatment of pyridine-2-carboxyaldheyde with 2-aminomethylpyridine (mol/mol = 2:1) in dichloromethane in the presence of triacetoxyborohydride yielded the tpa ligand in 89 % yield.…”