Chemical Environment Effects on the Photophysical Behavior of Two-Photon Materials
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Chemical Environment Effects on the Photophysical Behavior of Two-Photon Materials Jeremy C. Collette and Aaron W. Harper* Loker Hydrocarbon Research Institute, University of Southern California, Los Angeles, California 90089-1661 U.S.A. ABSTRACT A set of six new two-photon engineered diethylamino-substituted styryl pyrazine (DEASP) dyes have been developed as chemically responsive chromophores. This work employs UV/Vis spectroscopy to draw structure-optical property relationships and to quantify the solvatochromic effect observed for these dyes. Absorbance profiles for each of these dyes have been measured in 22 solvents ranging from very nonpolar (TMS) to very polar (water). Absorbance maxima of the longest wavelength π→π* transitions have been correlated to nine empirical scales of solvent polarity, and a comparative analysis is presented. Dimroth & Reichardt’s and Kamlet & Taft’s single parameter scales have been recalculated with spectral data obtained for the six DEASP dyes. The correlation of these established and recalculated scales are shown and discussed. DEASP chromophores are found to exhibit high sensitivity to their chemical environment and exceptional range as solvatochromic probes. Current models of solvatochromism, based on dipolar probes, cannot account for the solvatochromism observed in our quadrupolar dyes, and fail to describe the effect of the chemical environment on this family of twophoton dyes. The need to develop a more universal model of solvation incorporating higher order moment contributions is apparent.
INTRODUCTION As two-photon materials gain importance in the development of advanced materials for applications such optical limiting and optical data storage, a greater understanding of the physical interactions between these molecules and their environment becomes imperative. In the past decade, it has been shown that chromophores based on push-pull electron-donor/electron-acceptor motifs exhibit exceptional two-photon responses [1]. It has also been shown that the polarizabilities of such two-photon chromophores greatly affect their two-photon absorption cross-sections [2]. An understanding of how the chemical environment affects the photophysical behavior of two-photon materials will help develop more reliable structure-optical property relationships and will allow researchers to better predict the success of these materials in advanced applications and devices. In order to understand the role of the solvent shell in the solvent sensitive nature of the absorptive and emissive properties of some two-photon materials and to quantify the effect of the chemical environment on photophysical properties of these materials, we employ nine of the most commonly recognized single parameter empirical scales of solvent polarity. We correlate the solvatochromism observed in a family of six diethylamino-substituted styryl pyrazine (DEASP) dyes with these solvent polarity
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