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 (NBu2bipy) and related dipolar ([ZnY2(NBu2bipy)] (Y = Cl, CF3CO2), [Zn(2,2’-bipyridine)2(NBu2bipy)][PF6]2) and octupolar ([Zn(NBu2bipy)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.