Third-order nonlinear optics, dithiolene

Since Chapter 6 (352) in this volume is devoted to the luminescence and photochemistry of dithiolene complexes, these aspects will not be developed here. In this section, we restrict ourselves to the review of dithiolene complex-based compounds exhibiting optical properties, such as strong infrared (IR) absorption and second- and third-order nonlinear optical properties. In the last part of this section, we will review the use of some dithiolene complexes for optical data storage (printers, developer, CD-ROM, etc.). Contrary to what was observed throughout the two previous sections, no particular dithiolene complex really dominates the domain of the molecular materials exhibiting interesting optical properties. 

Hill, C. A. S. Underhill, A. E. Winter, C. S. Oliver, S. N. Rush, J. D. Resonance Enhanced Third-order Nonlinearities in Metal Dithiolenes. In Organic Materials for Nonlinear Optics II Hann, R. A., Bloor, D., Eds. Royal Society of Chemistry London, 1991, pp 217-222. 

Some heteroleptic dithiolene complexes studied for their third-order NLO properties and involving the dmit or the mnt ligands are shown in Scheme 27 (455, 456). Only the dmit-containing complexes exhibit a large third-order optical nonlinearity, due to their larger planar conjugated system compared to the mnt analogues. 

Third-order NLO effects, of interest for potential applications, for example in optical limiting ° impose no symmetry constraints. Thus, studies on this type of nonlinearity have addressed both homoleptic and heteroleptic 1,2-dithiolene complexes. Among the members of the former class, study on TBA salts of monoanionic nickel Al5(l,2-dithiolene) complexes with ligands such as phdt , dddt , pddt , cddt, and -substituted 1,2-diphenyl-1,2-ethyl-enedithioate ° have been published. Underhill and co-workers have reported on the nonlinear properties of unsymmetrically substituted w(l,2-dithiolene) complexes, such as iw[l-butyl-2-phenylethene-l,2-dithiolato(2 )-S,S ]nickel(II), embedded in PMMA-based composites (PMMA=polymethylmethacrylate), or in sol-gel materials.As regards the latter class, some works have dealt with complexes containing mnt and dmit ligands. ... 

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