Two novel mononuclear heteroleptic Ru(II) photosensitizers with 2-(1H-benzo[d]imidazol-2-yl)quinoline derivatives were designed and successfully synthesized. The facile synthesis and their photophysical properties are investigated. Both the Ru(II) complexes i.e., [RuII(bpy)2(L1)](ClO4) : [1](ClO4) and [RuII(bpy)2(L2)](ClO4)2 : [2](ClO4)2 {L1 = 2-(1H-benzo[d]imidazol-2-yl)quinoline and L2 = 2-(1-methyl-1H-benzo[d]imidazol-2-yl)quinoline} have been meticulously characterized by different spectroscopic and analytical techniques such as FT–IR, 1H NMR, ESI mass spectra, UV–vis and fluorescence spectroscopy, etc. Molecular structures of [1](ClO4) and [2](ClO4)2 have been determined by a single-crystal X-ray structure diffraction study. Redox and spectral properties of the synthesized Ru(II) complexes were examined along with their corresponding ligands and compared with the classic homoleptic [RuII(bpy)3](PF6)2. The effects on substituents in the ligand backbone were scrutinised. The emission behaviour of both [1](ClO4) and [2](ClO4)2 revealed relatively long-lived emissive 3MLCT and bathochromic shift (~ 715 nm) while compared with [RuII(bpy)3](PF6)2 (~ 605 nm). Fairly weak quantum yields for [1](ClO4) and [2](ClO4)2 : ∼ 0.00299 and ∼ 0.00295 with half-lives 181.57 ns and 198.89 ns, respectively, suggested different non-radiative emission pathways. Additionally, for [1](ClO4) and [2](ClO4)2, electrochemical reduction of carbon dioxide (CO2) in dry acetonitrile solvent was performed and showed great promises for future designing of electrochemical reduction of CO2. Graphical abstract: Two mononuclear heteroleptic Ru(II) photosensitizers [1](ClO4) and [2](ClO4)2 containing 2-(1H-benzo[d]imidazol-2-yl)quinoline ligand were synthesized and investigated via FT–IR, 1H NMR, ESI mass spectra, UV–vis, time-resolved photoluminescence spectroscopy, X-ray structure, etc. Both [1](ClO4) and [2](ClO4)2 showed great promises for electrochemical reduction of carbon dioxide in dry acetonitrile.[Figure not available: see fulltext.] © 2022, Indian Academy of Sciences.