Spectroelectrochemistry in the Switching of Molecular Properties

Some accounts on the redox-induced switching of hyperpolarisabilities utilised penta-ammine ruthenium complexes bearing substituted 4,4 -bipyri-dinium coligands. The intense bipyridinium Ru LMCT band at 580 to 636 nm bleaches upon reduction of the metal centre, thus switching off their quadratic NLO response. The oxidation of the ferrocene donor in an ethenyl-linked ferrocene-nitrothiophene dyad likewise results in a decrease of the quadratic NLO response by about one order in magnitude. Oxidation-state-dependent quadratic NLO performance has also been noted by Lapinte and coworkers who compared the complexes Cp (dppe)Fe—C=CPh, Cp (dppe)Fe-C=C- 2(p-C6H4-l,4), Cp (dppe)Fe-C=C- 2(g-C6H4-l,3), 

Other work has demonstrated that it is possible to switch ON and OFF luminescence by reduction/oxidation, and it has been demonstrated that such switching is possible inside an OTTLE cell. Many alkynyl complexes, especially those of rhenium, platinum,copper, silver or gold are highly luminescent from their excited MLCT or metal perturbed 71 states. This opens up the possibility to significantly influence their emissive properties by redox processes. An interesting example is found in recent work of Wong et Unlike other rhenium(I)-alkynyl complexes, heterobimetallic 

UV-Vis-NIR spectroelectrochemical traces (top right) upon oxidation of [ Cl(dppe)2Ru-C=C-C6H4-4- 3C6H3-l,3,5] (left) closed and open aperture Z-scan traces for the complex and its trioxidised form at 800 nm using 100-fs pulses. Neutral Closed aperture (squares), open aperture (circles) trication closed aperture (triangles), open aperture (diamonds). Drawn out theoretical curves assume a thin sample approximation. Adapted with permission from ref 184. 

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