Synthesis and photophysical characterisation of luminescent zinc complexes with 5-substituted-8-hydroxyquinolines

New 5-substituted-8-hydroxyquinoline ligands HLn (1-3), in which the quinoline and the p-N,N-dimethylphenyl fragments are connected through the -N=N- (1), -CH=N- (2) or -CH2-NH- (3) group, were designed and synthesised. Their reaction with a Zn(II) salt gave the pertinent Zn(L-n)(2) complexes (4-6). The compounds 1-4 and 6 are stable in solution and their photophysical properties were explored. Zinc complexes 4 and 6 are both luminescent (4, lambda(em) : 620 nm, Phi< 1 x 10(-4); 6, λ(em) : 475 nm, Φ = 7 x 10(-3)), although the states responsible for the radiative deactivation processes were different: CT in nature for 4 and from π-π* transition localised on the quinoline fragment for 6. The roles exerted by both the metal and bridge on the photophysical properties are discussed.