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Degree

PhD, University of Cincinnati, Arts & Sciences : Chemistry, 2003.

Abstract

Neutral square planar platinum(II) diimine complexes undergo self-quenching in fluid solution, characterized by an increase in the emission decay rate with concentration. The corresponding quenching rates (10 ⁹ -10 ^{10 -1} s ^-1 ) are nearly diffusion limited. The accumulated evidence suggests that an excited platinum complex, (M*) reacts with a ground-state complex, (M), to form an excimer, (M2*), which rapidly relaxes to give two ground-state complexes. These complexes possess many attractive properties for use in application such as DNA recognition and chemical sensing. However, because the self-quenching rates are nearly diffusional, this behavior presents serious problems for applications demanding a long-lived excited state. As a result, there is great interest in learning to control the self-quenching behavior. Three possible interactions have been proposed to stabilize the excimer: (i) diimine-diimine interactions, (ii) metal-metal interactions, and (iii) a combination of these interactions. Efforts to distinguish between these possibilities have been hampered by short lifetimes and low quantum yields of the excimers. Consequently, we have turned our efforts toward cross-quenching reactions which are similar to self-quenching with the distinction that the excited monomer, M*, reacts with a different ground-state complex, Q, presumably to form an exciplex, MQ*. Through steady-state and time-resolved cross-quenching studies of Pt(tmphen)(tdt) with quenchers having various steric and electronic properties, we were able to investigate the mechanism of quenching. Rapid rates of cross-quenching (10 ⁹ 10 ¹⁰ M ^-1 s ^-1 ) were only observed when the quencher was another platinum(II) diimine complex. Energy transfer and outer-sphere electron transfer were ruled out as possible quenching mechanisms based on the driving forces for these reactions. The effects of both steric and electronic properties of the platinum(II) diimine quenchers on the observed rate constants have been examined in detail. The accumulated data are consistent with metal-metal interactions playing a critical role in cross-quenching.

Keywords

self-quenching; cross-quenching; excimer formation; plotinum(II) Diimine Complexes; luminescence

Advisor

Dr. William B. Connick

Pages

187p.

Document number: ucin1070634712
Permalink: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1070634712

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