Effect of Coordination Modes on the Tunable Luminescence of 1,10-Phenanthroline-Based Complexes

Two luminescent compounds [Zn(L)(2)](ClO4)(2) (1) and [Na(L)(MeOH)(mu-ClO4)](n) (2) are obtained from the reactions of 2,9-bis(carbomethoxy)-1,10-phenanthroline (L) with corresponding hydrated perchlorate salts in MeOH. Their crystal structures are determined by X-ray crystallography. 1 is a mononuclear 8-coordinate Zn2+ compound and 2 is a ClO4--bridged 1D polymer, where the ligand L exhibits different coordination modes (carbonyl O vs methoxyl O coordination). Although the luminescence of these two compounds originates similarly from the ligand-centered pi ->pi* transitions, it is interesting to note that their emissions are significantly influenced by the different coordination modes of L. The relationship between their structures and emission properties has been investigated in detail. The stability and energy difference between these two coordination modes in these two compounds are analyzed by Time-dependent density functional theory (TD-DFT) calculations.