Two-photon absorption properties of Zn(II) complexes: Unexpected large TPA cross section of dipolar [ZnY2(4,4′-bis(para-di-n-butylaminostyryl)-2,2′-bipyridine)] (Y = Cl, CF3CO2)

The two-photon absorption (TPA) properties of 4,4'-bis(para-di-n-butylaminostyryl)-2,2'-bipyridine (NBu(2)bipy) and related dipolar ([ZnY2(NBu(2)bipy)] (Y = Cl, CF3CO2), [Zn(2,2'-bipyridine) (2)(NBu(2)bipy)][PF6](2)) and octupolar ([Zn(NBu(2)bipy)(3)][PF6](2)) complexes were investigated by the two-photon emission (TPE) technique in a femtosecond regime, working in the 730-930 nm spectral range. We found, in contrast with previous literature data, that the TPA enhancement upon coordination of a TPA active ligand to a metal center may be larger in the dipolar rather than the corresponding octupolar complex, the response being easily modulated by the choice of the ancillary ligands. (C) 2009 Elsevier B.V. All rights reserved.