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The molecular and condensed phase optical excitations of 4-(4,4-bis((trifluoromethyl)sulfonyl) -1,3-butadienyl)-N,N-dimethyl-benzeamine
Abstract
A complete study of the electronic states of the molecular dye 4-(4,4-bis ((trifluoromethyl)sulfonyl) -1,3-butadienyl) -N,N-dimethyl-benzeamine (FSMB) is reported. The investigation revealed that FSMB exists as two valence tautomers; a benzenoid form and a quinoidal form. These can be selectively stabilized by solvent choice. In carbon tetrachloride solution the benzenoid species is the stable one but may be photoconverted into the quinoidal form. Polarized specular reflection spectra of FSMB crystals at 293 K, 10 K, and a number of intermediate temperatures were obtained. These revealed the presence of an electronic transition, the H band, which arises from dimeric interactions. This band's intensity demonstrated a marked temperature dependance similar to that previously observed for the J band of pseudoisocyanine crystals. The existence of several faces which contain the b-axis allowed a study of the monoclinic FSMB crystal free from axial and directional dispersion. This allowed observation of effects attributed to spatial dispersion for the b-axis spectra of a molecular crystal. The ac-factor group spectra of these faces, like that of many dyes, exhibited a strong directional dispersion. The (101) face spectra show high reflectivity along both principal directions. This quasi-metallic reflection indicates that the crystal should support exciton surface polaritons (ESP) along both principal directions. By using attenuated total reflection (ATR) spectroscopy, the ESP dispersion curve for both principal directions and an intermediate direction were measured. The measured curves are in good qualitative agreement with curves calculated by using the bulk dielectric function determined from the single crystal spectra and macroscopic electromagnetic theory. This theory was generalized for use with a complex dielectric tensor and arbitrary crystal orientations. The largest deviation occurs within the energy region where the spatial dispersion occurs in the reflection spectra. This is taken as further confirmation that the observed anomalies in the b-axis reflection spectra are due to spatial dispersion.
Subject Area
Chemistry
Recommended Citation
Ries, Paul Denis, "The molecular and condensed phase optical excitations of 4-(4,4-bis((trifluoromethyl)sulfonyl) -1,3-butadienyl)-N,N-dimethyl-benzeamine" (1988). ETD collection for University of Nebraska-Lincoln. AAI8907535.
https://digitalcommons.unl.edu/dissertations/AAI8907535