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The development of metal complex-based photoluminescent multifunctional materials is of great importance. Two cyclometalated Ir(III) polypyridyl complexes, 1PF6 and 2PF6 of dichloro and dibromo-substituted 1,10-phenanthroline ligands, have been developed and characterized by various spectroscopic means and single-crystal X-ray diffraction. Both the complexes, in addition to C–H···π interactions, show C–X···π halogen bonding interaction in the solid state. Two perchlorate analogues, 1ClO4 and 2ClO4, were also prepared to see the supramolecular interactions in the solid state. The crystal structures show the presence of C–Cl···O halogen bonding interaction in the solid state. Hirshfeld analysis for all the crystals supports the presence of halogen bonding and hydrogen bonding interactions, helping in intermolecular packing. Compounds 1PF6 and 2PF6 show very bright luminescence in chlorinated solvents and the solid state but weakly emit in most nonchlorinated solvents. The enhanced luminescence of 1PF6 and 2PF6 in the chlorinated solvent may be due to the aggregation, caused by the weak supramolecular interactions between the neighboring substituted phenanthroline ligand and halogen bonding interactions. The aggregation in the chlorinated solvent has been supported by scanning electron microscopy, transmission electron microscopy, and dynamic light scattering. Comparison of 1H NMR spectra of 1PF6 in acetone-d6 and a mixture of acetone-d6 and CDCl3 shows the broadening of the peaks in the presence of a high amount of CDCl3, further supporting the aggregation in chlorinated solvents. Quantum yield (ϕPL) and excited-state lifetime (τav) of 1PF6 and 2PF6 are increased significantly in all the chlorinated solvents. The ground- and excited-state TDDFT calculations were carried out to assign absorption and luminescence bands of 1PF6 and 2PF6.
Kashyap et al. (Thu,) studied this question.