Search

The structure-property correlations and control of electronic excited states in transition metal complexes (TMCs) are of high significance for TMC-based functional material development. Within these studies, a series of Re(I) carbonyl complexes with aryl-substituted 2,6-di(thiazol-2-yl)pyridines (Ar n -dtpy) was synthesized, and their ground- and excited-state properties were investigated. A number of condensed aromatic rings, which function as the linking mode of the aryl substituent, play a fundamental role in controlling photophysics of the resulting [ReCl(CO) 3 (Ar n -dtpy-κ 2 N)]. Photoexcitation of [ReCl(CO) 3 (Ar n -dtpy-κ 2 N)] with 1-naphthyl-, 2-naphthyl-, 9-phenanthrenyl leads to the population of 3 MLCT. The lowest triplet state of Re(I) chromophores bearing 9-anthryl, 2-anthryl, 1-pyrenyl groups is ligand localized. The rhenium(I) complex with appended 1-pyrenyl group features long-lived room temperature emission attributed to the equilibrium between 3 MLCT and 3 IL/ 3 ILCT. The excited-state dynamics in complexes [ReCl(CO) 3 (9-anthryl-dtpy-κ 2 N)] and [ReCl(CO) 3 (2-anthryl-dtpy-κ 2 N)] is strongly dependent on the electronic coupling between anthracene and {ReCl(CO) 3 (dtpy-κ 2 N)}. Less steric hindrance between the chromophores in [ReCl(CO) 3 (2-anthryl-dtpy-κ 2 N)] is responsible for the faster formation of 3 IL/ 3 ILCT and larger contribution of 3 ILCT anthracene → dtpy in relation to the isomeric complex [ReCl(CO) 3 (9-anthryl-dtpy-κ 2 N)]. In agreement with stronger electronic communication between the aryl and Re(I) coordination centre, [ReCl(CO) 3 (2-anthryl-dtpy-κ 2 N)] displays room-temperature emission contributed to by 3 MLCT and 3 IL anthracene / 3 ILCT anthracene → dtpy phosphorescence. The latter presents rarely observed phenomena in luminescent metal complexes.

Methyl-substituted 8-hydroxyquinolines (Hquin) were successfully used to synthetize five-coordinated oxovanadium(IV) complexes: [VO(2,6-(Me) 2 -quin) 2 ] ( 1 ), [VO(2,5-(Me) 2 -quin) 2 ] ( 2 ) and [VO(2-Me-quin) 2 ] ( 3 ). Complexes 1 - 3 demonstrated high catalytic activity in the oxidation of hydrocarbons with H 2 O 2 in acetonitrile at 50 °C, in the presence of 2-pyrazinecarboxylic acid (PCA) as a cocatalyst. The maximum yield of cyclohexane oxidation products attained was 48%, which is high in the case of the oxidation of saturated hydrocarbons. The reaction leads to the formation of a mixture of cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone. When triphenylphosphine is added, cyclohexyl hydroperoxide is completely converted to cyclohexanol. Consideration of the regio- and bond-selectivity in the oxidation of n-heptane and methylcyclohexane, respectively, indicates that the oxidation proceeds with the participation of free hydroxyl radicals. The complexes show moderate activity in the oxidation of alcohols. Complexes 1 and 2 reduce the viability of colorectal (HCT116) and ovarian (A2780) carcinoma cell lines and of normal dermal fibroblasts without showing a specific selectivity for cancer cell lines. Complex 3 on the other hand, shows a higher cytotoxicity in a colorectal carcinoma cell line (HCT116), a lower cytotoxicity towards normal dermal fibroblasts and no effect in an ovarian carcinoma cell line (order of magnitude HCT116 > fibroblasts > A2780).