Photochemical Sciences Ph.D. Dissertations

Synthesis and Photophysics of Platinum (II) Diimine Acetylide Complexes

Date of Award

2007

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Felix Castellano

Abstract

The present thesis describes the synthesis and photophysics of a variety of platinum(II) diimine acetylide complexes containing mixed metal-ligand to ligand charge transfer excited states. In the second chapter, the synthesis, structural characterization, and photoluminescence properties of six Pt(II) diimine complexes, Pt(dbbpy)(C≡CR)2 [dbbpy = 4,4’-di(tert-butyl)-2,2’-bipyridine; R = -SiMe3, -C≡C-SiMe3, - t-Bu, -CH2CH2CH3, -H and -C≡CH], are presented. Pt(dbbpy)(C≡C-tBu)2 serves as a model complex with a carbon-based ligand for which the photophysical properties of two silicon-bearing complexes are compared in CH3CN, dichloromethane, 2-methyltetrahydrofuran (MTHF) and toluene. Pt(dbbpy)(C≡C-SiMe3)2 2 and Pt(dbbpy)(C≡C-C≡C-SiMe3)2 display visible absorptions with strong green emission while Pt(dbbpy)(C≡C-t-Bu)2 displays efficient, long-lived yellow emission. Direct side by side comparisons of Pt(dbbpy)(C≡C-SiMe 3) 2and Pt(dbbpy)(C≡C-tBu) 2suggest that the differences in the excited state energy result from the relative σ-donor strength of the acetylide ligands.

In the third chapter, the photophysical and electrochemical properties of a platinum(II) diimine complex bearing the bidentate diacetylide ligand tolan-2,2’-diacetylide (tda), Pt(dbbpy)(tda), are compared with two reference compounds, Pt(dbbpy)(C≡CPh)2 and Pt(dppp)tda [dppp = 1,3-bis(diphenylphosphino)propane], respectively. The rigidity imposed by the cyclic diacetylide ligand in Pt(dbbpy)(tda) leads to a reduction in nonradiative decay which increases its lifetime and quantum yield at room temperature. The 77 K emission spectrum of Pt(dbbpy)(tda) is from 3tda in nature, asserting that the charge transfer states are raised in energy relative to the 3tda levels in Pt(dbbpy)(tda) in the low temperature glass. Nanosecond transient absorption spectrometry was performed on all three compounds in CH2Cl2 at ambient temperature. For compounds Pt(dbbpy)(tda) and Pt(dbbpy)(C≡CPh)2, the major absorption transients are consistent with one-electron reduced complexes, corroborated by reductive spectroelectrochemical measurements performed at room temperature. As Pt(dppp)tda does not possess any charge transfer character, excitation into the π* orbitals of the tda ligand generates transient absorptions assigned to the ligand-localized triplet state.

In the forth chapter, the photophysical and electrochemical properties of another platinum(II) diimine complex bearing the tda ligand, Pt(mesBIAN)(tda) [mesBIAN = non-heterocyclic bidentate diimine ligandbis(mesitylimino)-acenaphthene] are studied. The presence of mesBIAN lowers the lowest unoccupied molecular orbital (LUMO) in energy, hence the charge-transfer absorption red shifts and the corresponding photoluminescence moves to near-IR range at room temperature.

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