The Relationship Between Molecular Structure and Spectroscopic Properties of a Series of Transition Metal-Containing Phe
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The Relationship Between Molecular Structure and Spectroscopic Properties of a Series of Transition Metal-Containing Phenylacetylene Oligomers and Polymers 1
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Thomas M. Cooper, Daniel G, McLean , and Joy E. Rogers Materials and Manufacturing Directorate, Air Force Research Laboratory, Wright-Patterson, Air Force Base, OH 45433, USA 1 Science Applications International Corporation, Dayton, OH 45434, USA 2 Technical Management Concepts International, Dayton, OH 45433, USA ABSTRACT To develop novel nonlinear dyes for photonic applications, we synthesized a series of transition metal-containing phenylacetylene oligomers and polymers. The optical properties of these compounds were measured by UV/Vis, fluorescence, and flash photolysis experiments. As the number of oligomer units increased, the transition energies decreased. A solvatochromism experiment suggested the fluorescing state was different from the absorbing state. As a group, the spectra of the polymeric versions of these complexes were red shifted from the spectra of the oligomers. The polymeric complexes had less clear trends relating the number of oligomer units to transition energies. A comparison of a low molecular weight and a high molecular weight polymer showed the degree of polymerization caused spectroscopic shifts comparable to the number of phenylacetylene units in the monomer unit. INTRODUCTION In recent years there has been increasing interest in the optical and nonlinear optical properties of transition metal complexes, both in oligomeric, polymeric and polygonal forms[13]. In particular, free-standing thin films of these polymers have been shown to have large third order hyperpolarizabilities[4]. Recent work has also shown two photon absorption[5] and nonlinear absorption promoting formation of the triplet state[6-8]. To increase our understanding of the excited state dynamics of these compounds, we synthesized a series of Ptalkynyl complexes and polymers and performed a variety of spectroscopic characterization experiments. EXPERIMENTAL Trans-bis(tri-n-butylphosphine)bis(alkynyl))Pt complexes and polymers poly(transbis(tri-n-butylphosphine)alkynyl)Pt) were prepared according to literature procedures[9, 10]. All spectroscopic measurements were performed on THF solutions. UV/Vis spectra were collected on a Cary 500 spectrophotometer. Emission spectra were collected on a Perkin-Elmer model LS 50B fluorometer with both excitation and emission bandwidths set at 5 nm. Fluorescence quantum yields referenced to a quinine sulfate standard were collected according to published procedures[11]. Phosphorescence spectra were obtained from degassed samples. Nanosecond transient absorption measurements employed the technique of laser flash photolysis. The third harmonic(355 nm) of a Q-switched Nd:Yag laser(Continuum YG661, pulse with ca. 18 nsec) was used for laser flash excitation. Preliminary investigation of processing these materials to high optical quality thin films was performed through surface roughness measurements. To C5.21.1
measure film surface
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