Dual emission and multi-stimuli-response in iridium(III) complexes with aggregation-induced enhanced emission: applications for quantitative CO2 detection

Four new Ir(III) complexes with the general formula [IrHCl(C<^>N)(PPh3)(2)] containing different conjugated Schiff base ligands (C<^>N) have been synthesized and characterized by H-1, C-13, and P-31 NMR, HRMS, and IR spectra and one of them by single crystal X-ray diffraction. Their photophysical properties in solution and in the solid state have been analyzed and three main practical results have been obtained: (i) a dual fluorescent and phosphorescent emissive complex in solution, (ii) successful acid/base sensing in the solid state and (iii) quantitative CO2 detection. Quantum chemical calculations have been employed to assign the character of the lowest excited states. A plausible explanation for the observed aggregation induced enhanced emission (AIEE) is given, based on the restriction of intramolecular motions due to the effect of intermolecular C-H. . .pi and C-H. . .Cl type interactions upon aggregation.