Abstract
In this paper, the nonlinear absorption properties of two complexes consisting of Ru(C≡CPh)(C≡C)(dppe)2 (dppe = Ph2PCH2CH2PPh2) as electron donor (D) and 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole as electron acceptor (A) units in two different arrangement, i.e., A–D–A and D–A–D, are presented. They were measured in solution by the femtosecond open-aperture Z-scan method. The complexes show moderate two-photon absorption cross-sections σ(2) of several hundred to one thousand GM (here 1 GM = 10−50 cm4 s molecule−1 photon−1). Although they are formed by the same building units, it was found that the two-photon absorption values of the D–A–D arrangement are six times higher than that of the A–D–A one. This difference can be explained by the number of metal cores (one or two ruthenium centers), the geometrical configurations of the complexes (more or less planar), and the resonance enhancement by lowering the intermediate state.
Highlights
Two-photon absorption (TPA), one of the nonlinear absorption (NLA) processes, has attracted considerable attention in the last few years because of its applications in various fields, such as 3D fluorescence imaging and control of biological systems, 3D-microfabrication, optical limiting, and so on [1,2]
In complex Ru-1 two di(thienyl)benzothiadiazole units are linked by a Ru(II) σ-acetylide bridge, forming a A–D–A type arrangement, while in Ru-2, Inorganics 2019, 7, 67; doi:10.3390/inorganics7050067
The molar absorption coefficients are similar for dichloromethane solution (10 M) are shown
Summary
Two-photon absorption (TPA), one of the nonlinear absorption (NLA) processes, has attracted considerable attention in the last few years because of its applications in various fields, such as 3D fluorescence imaging and control of biological systems, 3D-microfabrication, optical limiting, and so on [1,2]. A large number of compounds have been investigated and extensive efforts were devoted to clarifying the structure-property relationship. Σ-acetylide complexes, well-known for their second- and third-order optical nonlinearities [3,4,5,6,7], are of great interest because they tend to have very large two-photon absorption cross-sections [8,9,10,11]. Σ-acetylide complexes (Ru-1 and Ru-2, Figure 1) were synthesized [4,5,14] In these complexes, the metal centers act as donor (D) groups of a donor–acceptor (D/A) system, where the acceptor (A) is the organic fragment 4,7-di(2-thienyl)benzo[c][1,2,5]thiadiazole. In complex Ru-1 two di(thienyl)benzothiadiazole units are linked by a Ru(II) σ-acetylide bridge, forming a A–D–A type arrangement, while in Ru-2, Inorganics 2019, 7, 67; doi:10.3390/inorganics7050067 www.mdpi.com/journal/inorganics
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