Exploration of photophysical, electrochemical and electronic properties of rhenium(I) complexes incorporating acridine moiety: Role of coligands in tuning the spectral and electronic properties

Abstract

Dinuclear rhenium complex possesing fac-[Re(CO)₃]⁺ core having the formula [Re₂(CO)₆(L)₂] (1) and bearing acridine moiety has been synthesized in excellent yields by the reaction of acridin-4-ol with [Re(CO)₅Cl] in 1:1 ratio in toluene under argon atmosphere. Here, L is the deprotonated form of acridin-4-ol. The reaction of the synthesized dinuclear complex with imidazole (Im), N-methylimidazole (N-MeIm), quinoline (Quin), and 2-methylquinoline (Me-Quin) in dry dichloromethane furnished the mononuclear complexes with the formula, [Re(CO)₃L(Im)] (1a), [Re(CO)₃L(N-MeIm)] (1b), [Re(CO)₃L(Quin)] (1c), and [Re(CO)₃L(Me-Quin)] (1d) in good yields. Molecular structure of fac-[Re₂(CO)₆(L)₂] was confirmed by single crystal X-ray diffraction. Elemental analysis, ESI mass spectroscopy and ¹H NMR spectroscopy were utilised to confirm the formation of the desired complexes. The as-synthesized complexes were further utilised to explore the photophysical, electrochemical, and electronic properties. Photophysical measurements reveal a bathochromic shift upon incorporation of different coligands into the fac-[Re(CO)₃]⁺ core. The emission behaviour of the molecules is consistent with an admixture of ³MLCT and ³ILCT character. To gain insight into the charge transfer-associated conducting nature of the molecules, Electrochemical Impedance Spectra analysis was carried out. Herein, the coligands played a crucial role in tuning the opto-electronic properties of the designed complexes. The ground and excited state geometries of the molecules were explored by theoretical calculations, employing DFT and TD-DFT measurements.