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Third‐Order Nonlinear Optical Properties of DA‐salen‐Type Nickel(II) and Copper(II) Complexes

2006; Wiley; Volume: 2006; Issue: 17 Linguagem: Inglês

10.1002/ejic.200600017

1099-0682

João Tedim, Sónia G. Patrício, R. Bessada, Rui Morais, Carla Sousa, Manuel B. Marques, Cristina Freire,

Porphyrin and Phthalocyanine Chemistry

Abstract Third‐order nonlinear and linear optical properties ofnickel(II) and copper(II) complexes with salen ligands, functionalised with electron donor/acceptor groups (DA‐salen), have been investigated in solution by the Z‐scan technique using an Nd:YAG laser ( λ inc = 1064 nm) and UV/Vis spectroscopy. The [M(DA‐ salen )] complexes exhibit positive nonresonant nonlinear refractive indexes ( n 2 I ) in the range27.0–8.50 · 10 –21 m 2 W –1 and nonlinear absorption coefficients ( α 2 I ) within the range 1.80–26.0 · 10 –17 m W –1 . The latter values correspond to less than 10 % of the overall magnitude of the third‐order susceptibility, | χ 3 |, which is the result of the absence of electronic transitions near λ inc = 1064 nm. For the group of Ni II complexes, the highest n 2 I values are exhibited by the complexes with aromatic diimine bridges and large π‐electron delocalisation, which leads to intense electronic charge‐transfer bands ( ϵ > 16000 mol –1 dm 3 cm –1 ) in the region λ = 275–500 nm. The complexes that exhibit charge‐transfer bands near λ inc /2 = 532 nm, also show the highest α 2 I values, a consequence of multiphoton absorption processes. For the group of Cu II complexes, the highest n 2 I value is also observed by the complex that exhibits the most intense charge‐transfer bands in the region λ = 275–475 nm. Between Ni II and Cu II complexes with the same DA‐salen ligands, those of copper show always higher n 2 I values, indicating that NLO responses can also be fine‐tuned by the metalcentre. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)