Density-functional analysis of substituent effects on photochemistry of Ru(II)-polypyridyl complexes

Studies on complexes of the type: [Ru(en) 2 L 2 ] 2+ , en = ethylenediamine, L = pyridine (Py), 2-, 3-, or 4-methylpyridine (PyCH 3 ), 2-, 3-, or 4-acetylpyridine (PyCOCH 3 ) and 2-, 3-, or 4-cyanopyridine (PyCN) are carried out using the DFT method and B3LYP/LanL2DZ level of theory. The trends in substituent modifications (type and position) caused by electron-releasing group (methyl) and electron-withdrawing groups (acetyl and cyano) on the electronic structure and related properties have been investigated. Computational results show: first, substituents exert interesting effects on both ground and excited states of the examined complexes. Second, electron-releasing group (methyl), for example, causes a blue shift in the electronic MLCT ground band. However, electron-withdrawing groups (acetyl and cyano) cause a red shift in the electronic MLCT ground band. Third, substituent modification (by influencing the geometrical parameters, like bond length and angle, and thus the dependent optical properties of the involved complexes) helps in designing and engineering effective and selective colorimetric chemosensors to be employed in chemosensation.