Color Tuning and Noteworthy Photoluminescence Quantum Yields in Crystalline Mono/Dinuclear ZnII Complexes

Series of ZnII complexes with coordinated pyridine and a O,N,O tridentate core are reported. Four species of the general formula ZnLiPy2 were synthesized, where Li is a substituted ((aroylhydrazono)methyl)-3-hydroxyphenyl-4-(octyloxy)benzoate. The structure of the four mononuclear complexes and of dinuclear Zn2L24Py2 was solved by single crystals X-ray analysis. By TGA-DSC analysis and optical observation a nematogenic phase behavior was detected for ligands only and not for complexes. Photoluminescence spectra were recorded both in solution and in solid state Only the complexes showed a noteworthy photoluminescence in the solid state with tunable wavelength by varying the aroyl group. Medium to very high PL quantum yields were recorded on the crystalline complexes obtained in their mononuclear coordination environment. In the case of 4-nitrobenzoyl substituent a dinuclear complex with formula Zn2L24Py2 showed an unprecedent exceptionally high PLQY value. Both periodic and molecular DFT calculations were performed to rationalize the absorbance of these complexes at “one particle” level.