Enhanced two-photon excited fluorescence of mercury complexes with a conjugated ligand: Effect of the central metal ion

Based on the chelation of 6-phenyl-4′-(4-[4-(diphenylamino)styryl]phenyl)-2,2′-bipyridine (L) to Hg(II) ions, two luminescent coordination complexes HgBr2L (1) and HgI2L (2) were prepared. Compared with the free ligand, the complexes exhibit enhanced two-photon excited fluorescence and larger two-photon absorption cross-section values. Time-dependent density functional theory calculations were carried to investigate the influence of central metal ion on the characteristic of charge transition of the complexes. The results indicated that the complexation of the ligand with Hg(II) ion causes stronger intramolecular charge transfer, leading to enhanced two-photon absorption of the complexes.