Synthesis, crystal structures, photophysical, electrochemical studies, DFT and TD-DFT calculations and Hirshfeld analysis of new 2,2′:6′,2′′-terpyridine ligands with pendant 4′-(trimethoxyphenyl) groups and their homoleptic ruthenium complexes

Two new ligands, 4′-(2,3,4-trimethoxyphenyl)-2,2′:6′,2′′-terpyridine ( L 1 ) and 4′(2,4,5-trimethoxyphenyl)-2,2′:6′,2′′-terpyridine ( L 2 ), and their homoleptic ruthenium( ii ) complexes, [Ru( L 1 ) 2 ](PF 6 ) 2 ( 1 ) and [Ru( L 2 ) 2 ](PF 6 ) 2 ( 2 ), were synthesized and characterized by elemental analysis, 1 H and 13 C{ 1 H} NMR spectroscopy, FT-IR spectroscopy and single crystal X-ray diffraction. The crystals of these compounds contain CH F, OH F, CH O, CH π and/or π π intermolecular secondary interactions, resulting in supramolecular architectures. Hirshfeld surface analysis of all four compounds was also carried out to determine the intermolecular interactions. We investigated the photophysical properties of L 1 , L 2 , 1 and 2 by UV-Visible absorption and fluorescence emission spectroscopy and studied their electrochemical properties by cyclic voltammetry. In addition to n-π* and π-π* bands in the UV-Visible spectra of both ligands and complexes, a fairly strong and relatively broad 1 MLCT band appeared at λ max ∼ 500 nm in complexes 1 and 2 . The emission bands in ligands L 1 and L 2 appeared at λ em 429 and 426 nm, respectively, whereas in the complexes 1 and 2 , these bands showed red-shifts of 34 and 82 nm, respectively. Both L 1 and L 2 showed two oxidation peaks; however, only L 2 showed a significant reduction peak. Complexes 1 and 2 showed two oxidation peaks and two reduction peaks. The effects of increasing scan rate (100 to 1000 mV s −1 ) on the electrochemical behaviour of complexes 1 and 2 were also investigated. The experimentally observed structural and photophysical properties were supported by DFT and TD-DFT calculations. [Ru( L 1 ) 2 ](PF 6 ) 2 ( 1 ) and [Ru( L 2 ) 2 ](PF 6 ) 2 ( 2 ): X-ray structures, CH F/O, OH F/N, CH O/π, π π interactions, absorption and emission spectra, DFT/TD-DFT, Hirshfeld analysis.