Influence of para substituents in controlling photophysical behavior and different non-covalent weak interactions in zinc complexes of a phenol based “end-off” compartmental ligand

Abstract

Three dinuclear zinc(II) complexes with “end-off” compartmental ligands, namely 2,6-bis(N-ethylmorpholine-iminomethyl)-4-R-phenol (R = –CH₃, Cl, ^tBu) have been synthesized with the aim of exploring the role of the para substituent present in the ligand backbone in controlling the structural diversity, photophysical properties and different weak interactions of the complexes. All three species, with the general formula {2[Zn₂L(CH₃COO)₂][Zn(NCS)₄]}, show the complex anion Zn(NCS)₄²⁻ as a common structural feature decisive for crystallization. Interestingly, all of them possess several non-covalent weak interactions where the nature of the “R” group plays an essential role as exposed by DFT study. Besides exhibiting fluorescence behavior, the complexes also show para substitution controlled phosphorescence both at room and low temperature. Anisotropy studies suggest the existence of complexes 2 and 3 as dimers in solution. The origins of the unusual room temperature phosphorescence and fluorescence behavior of the complexes have been rationalized in the light of theoretical calculations.