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 ([ZnY(2)(NBu(2)bipy)] (Y = Cl, CF(3)CO(2)), [Zn(2,2'-bipyridine) (2)(NBu(2)bipy)][PF(6)](2)) and octupolar ([Zn(NBu(2)bipy)(3)][PF(6)](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.