Dipolar Copper(I) Complexes: A Novel Appealing Class of Highly Active Second-Order NLO-Phores

The second-order nonlinear optical (NLO) properties of the known heteroleptic complex [Cu(1,10-phenanthroline)xantphos][PF₆] (complex <b>1</b>) and the related new complexes [Cu(5-NO₂-1,10-phenanthroline)xantphos][PF₆] and [Cu(5-NO₂-1,10-phenanthroline)(dppe)][PF₆] (dppe = 1,2-bis(diphenylphosphino)ethane) (complexes <b>2</b> and <b>3</b>) were investigated in solution by the EFISH (Electric Field-Induced Second Harmonic generation) technique, working at a non-resonant wavelength of 1907 nm. It turned out that they are characterized by large μβ values (957-1100 × 10^-48 esu), much higher than that of the Disperse Red One benchmark. Unexpectedly, the homoleptic complex [Cu(2-mesityl-1,10-phenanthroline)₂][PF₆] (complex <b>4</b>) shows a similar high second-order NLO response. Quantum chemical calculations based on Density Functional Theory (DFT) methods have been carried out to give insight into the electronic structure of the investigated complexes in relation to NLO properties. This investigation, which represents the first EFISH study on copper(I) complexes, opens a convenient route for the development of low-cost dipolar NLO-active heteroleptic [Cu(P^P)(N^N)][PF₆] and homoleptic [Cu(N^N)₂][PF₆] complexes.