Enhanced third-order nonlinear optical properties determined in thin films using the Z-scan technique: bis(μ-4,4′-oxydibenzoato)bis[(4′-phenyl-2,2′:6′,2′′-terpyridine)cobalt(II)]

Abstract

π-Conjugated organic materials exhibit high and tunable nonlinear optical (NLO) properties, and fast response times. 4′-Phenyl-2,2′:6′,2′′-terpyridine (PTP) is an important N-heterocyclic ligand involving π-conjugated systems, however, studies concerning the third-order NLO properties of terpyridine transition metal complexes are limited. The title binuclear terpyridine CoIIcomplex, bis(μ-4,4′-oxydibenzoato)-κ3O,O′:O′′;κ3O′′:O,O′-bis[(4′-phenyl-2,2′:6′,2′′-terpyridine-κ3N,N′,N′′)cobalt(II)], [Co2(C14H8O5)2(C21H15N3)2], (1), has been synthesized under hydrothermal conditions. In the crystal structure, each CoIIcation is surrounded by three N atoms of a PTP ligand and three O atoms, two from a bidentate and one from a symmetry-related monodentate 4,4′-oxydibenzoate (ODA2−) ligand, completing a distorted octahedral coordination geometry. Neighbouring [Co(PTP)]2+units are bridged by ODA2−ligands to form a ring-like structure. The third-order nonlinear optical (NLO) properties of (1) and PTP were determined in thin films using the Z-scan technique. The title compound shows a strong third-order NLO saturable absorption (SA), while PTP exhibits a third-order NLO reverse saturable absorption (RSA). The absorptive coefficient β of (1) is −37.3 × 10−7 m W−1, which is larger than that (8.96 × 10−7 m W−1) of PTP. The third-order NLO susceptibility χ(3)values are calculated as 6.01 × 10−8 e.s.u. for (1) and 1.44 × 10−8 e.s.u. for PTP.