Experimental and theoretical investigations on spectroscopic properties of the imidazole-fused phenanthroline and its derivatives

Abstract

Two phenanthroline derivatives, 1H-imidazo[4,5-f][1,10]phenanthroline (imPhen) and 2-(9H-fluoren-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (Flu-imPhen), have been synthesized and characterized and the corresponding absorption and emission spectroscopic properties have been studied in CH2Cl2 solution. The imPhen exhibits the main two absorption bands at 282nm and 229nm and these bands are assigned as the typical π→π*(Phen) state. In addition, the weak absorption bands at 313nm associated with a shoulder near 302nm were assigned to the π→π*(Phen) state with partial charge transfer (CT) character. A similar absorption spectra are observed in the case of the Flu-imPhen in the region of 200–300nm, while the region of 300–400nm of the spectra are dominated by the characteristic π→π* transition of the fluorene moiety. imPhen shows the typical ligand-centered 1π→π* emission, while Flu-imPhen emits from the mixed 1π→π*/CT states. Density functional theory (DFT) and time-dependent density functional theory (TDDFT) were employed to rationalize the photophysical properties of these ligands studied. The theoretical data confirm the assignment of the experimental absorption spectra and the nature of the emitting states.