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Mono- and di-nuclear photoluminescent complexes of zinc(ii), cadmium(ii) and mercury(ii) of a chiral diimine ligand†
Suman Kundu,Suvendu Maity,Pinki Saha Sardar,Sanjib Ghosh,Prasanta Ghosh
Dalton Transactions Pub Date : 07/19/2013 00:00:00 , DOI:10.1039/C3DT51348C
Abstract

Reaction of α-pyridoin and N-phenyl-o-phenylenediamine affords 2-(2-(phenylamino)phenylimino)-1,2-di(pyridin-2-yl)ethanol (L) which undergoes cyclization to a chiral diimine, 2-methoxy-1-phenyl-2,3-di(pyridin-2-yl)-1,2-dihydroquinoxaline, LOMeOMe (conjugated 14πe system) in the presence of zinc(II), cadmium(II) and mercury(II) ions affording [Zn(LOMe)Cl2] (1), [Cd2(LOMe)2Cl4] (2) and [Hg2(LOMe)2Cl4] (3) complexes. Ligand L and complexes 1–3 are substantiated by elemental analyses, mass, IR, 1H NMR and UV-vis spectra including the single-crystal X-ray structures of 1 and 3. The possibility of the atropisomerism of L is restricted in cyclic LOMeOMe. L and complexes 1–3 are fluorescent in fluid solutions at 298 K (CH2Cl2: 1, λex = 470 nm, λem = 627 nm, Φ = 0.014, τavg = 2.5 ns; 2, λex = 430 nm, λem = 599 nm, Φ = 0.08, τavg = 7.6 ns; 3, λex = 415 nm, λem = 600 nm, Φ = 0.021, τavg = 2.8 ns). Time-resolved emission spectra (TRES) established that the two-component lifetimes of 1–3 are due to the existence of two conformers. Density functional theory (DFT) and time dependent (TD) DFT calculations authenticated that 1–3 complexes are fluorescent due to intra-ligand charge transfer (ILCT) to the πdiimines* orbital.

Graphical abstract: Mono- and di-nuclear photoluminescent complexes of zinc(ii), cadmium(ii) and mercury(ii) of a chiral diimine ligand
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