UBC Theses and Dissertations
Synthesis and characterization of photochromic platinum-coordinated dithienylethenes Roberts, Matthew
The syntheses and characterization of photochromic platinum-coordinated dithienylethenes (DTEs) are reported. Platinum acetylide complexes were investigated as potentially useful chromphores to integrate with photoresponsive DTEs. Acetylides were observed to be successful at promoting strong electronic interaction between the Pt atom and the DTE’s thienyl scaffold. As a result of platinum’s large spin-orbit coupling, these metal complexes exhibit a high propensity for generating excited states with triplet character upon photoexcitation. Consequently, platinum acetylide complexes were found to be effective sensitizers for population of DTE-localized triplet states via energy transfer between the two chromophores. Platinum terpyridine complexes were initially targeted because they exhibit long-lived excited states, whose lifetime could be potentially modulated by photoswitching of the appended DTE. In fact, selective irradiation of the Pt complex with visible light resulted in energy transfer from a metal-based excited state to the DTE chromophore, in either the ring-open or ring-closed state. The triplet excited state of the ring-open DTE was observed to be photoactive and underwent cyclization to the ring-closed form. The effect of the alkynyl linkage on energy transfer was studied by incorporating a longer, non-conjugated alkynyl linkage between the two chromophores. Lengthening the linker reduced excited-state interaction between the metal-based and DTE-localized states, but did not completely eliminate energy transfer. The high efficiency of metal-sensitized ring-closing in the Pt terpyridine system led to subsequent exploration of multifunctional systems, those containing more than one DTE. Symmetrical Pt(II)-bis(phosphine)bis(acetylide) complexes were used for the preparation of discrete model systems and extended oligomeric species. The Pt-acetylide linkage was successful in allowing photoswitching of multiple adjacent DTE chromophores while maintaining a conjugated pathway between DTE units. Optical and electrochemical characterization supported that adjacent DTEs are capable of electronic communication through the Pt center. Extended electronic delocalization observed when multiple adjacent DTEs are ring-closed makes this system suitable for applications utilizing π-conjugated materials.
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