“Diimine–NiII–Catecholate” Chromophores Based on Phenanthroline-Type Ligand Systems: Molecular Structure, Ligand-to-Ligand Charge Transfer, and Thermal Behavior

A series of chromophoric complexes Ni^II(3,6-Cat)(Phen) (1), Ni^II(3,6-Cat)(DPQ) (2), and Ni^II(3,6-Cat)(DPPZ) (3) (where 3,6-Cat is 3,6-di-tert-butylcatecholate dianion) has been synthesized using 1,10-phenanthroline (Phen), dipyrido[3,2-d:2',3'-f]quinoxaline (DPQ), and dipyrido[3,2-a:2',3'-c]phenazine (DPPZ). Chromophores 1–3 have a slightly distorted planar structure of the coordination environment and undergo photoinduced ligand-to-ligand intramolecular charge transfer (HOMO_donor → LUMO_acсeptor), thus demonstrating strong light absorption in visible and near-IR regions. Complexes 1–3 are characterized by high thermostability and complete transition to the vapor phase under reduced pressure conditions. Compound 1 has high volatility, which makes it a suitable candidate for further testing in the fabrication of optoelectronic devices by “evaporation–deposition” technology.