Transition states of the 3MLCT to 3MC conversion in Ru(bpy)2(phen derivative)2+ complexes

Electronic structures of ruthenium complexes [Ru(bpy)2(L)]2+ were studied by DFT calculations, where bpy is 2,2′-bipyridine and L’s are 1,10-phenanthroline (phen) derivatives. They are parent (1) and eight complexes with L = 4-phenyl-phen (2), 4,7-diphenyl-phen (3), 2,9-dimethyl-4,7-diphenyl-phen (4), 2,9-dimethyl-phen (5), 3,4,7,8-tetramethyl-phen (6), 5-amino-phen (7), 5-methyl-phen (8), and 3-phenylethynyl-phen (9). Those complexes except 7, and 9 were prepared and characterized.Three triplet (called here 3MLCT, 3MC1 and 3MC2) states were obtained in all the complexes. 3MC1 and 3MC2 states were found to have the elongated Ru–N bonds and large spin densities on Ru2+. The geometry optimization of the triplet state of ruthenium complexes leads to the elongation of two trans Ru–N bonds confirming the 3MC character. The correlation between quantum yields and (3MLCT – 3MC2) energy gaps was examined and discussed. Successive conversion paths of (3MLCT → 3MC1) and (3MC1 → 3MC2) of 1 and 5 were determined. Their activation energies were calculated to be very small.

Graphical abstractSpin densities were analyzed to characterize the triplet states and their conversion transition states in ruthenium complexes [Ru(bpy)2(L)]2+ by DFT calculations. Energy gaps between 3MLCT and ground states were compared with energies corresponding to wavelengths of emission spectra.Figure optionsDownload full-size imageDownload as PowerPoint slide