Synthesis and study of Re(I) tricarbonyl complexes based on octachloro-1,10-phenanthroline: Towards deep red-to-NIR emitters

To shift the emission of classical [Re(CO)(3)(N"N)X](0/+) complexes to the NIR region, we have proposed a novel and efficient design strategy based on perchlorination of the diimine (N"N) ligands. In pursuing this goal, we have exploited octachloro-1,10-phenanthroline (phen-Cl-8), a strong It-acceptor ligand, to synthesize complexes of [Re (phen-Cl-8)(CO)(3)Br], [Re(phen-Cl-8)(CO)(3)OTf], and [Re(phen-Cl-8)(CO)(3)(CH3CN)]OTf type. The emission of these compounds in solid and solution states is found to be significantly red-shifted by 131-186 nm compared to their parent H-analogs. The "perchloronation effect" most pronouncedly appears for [Re(phen-Cl-8)(CO)(3)Br], whose emission maxima are 685 and 730 nm in solid and solution states, i.e. red-shifted by 186 nm (0.539 eV) and 158 nm (0.543 eV), respectively, relative to [Re(phen)(CO)(3)Br]. The in-depth spectral and DFT studies indicate that the above complexes emit phosphorescence of (3)(M + X)LCT character (X = CO + L-an).