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Temperature dependent reflection and piezomodulated reflection spectroscopy of polydiacetylene single crystals
Abstract
Optical properties of the polydiacetylenes (PDAs) 2,4-hexadiyne-1,6-diol-bis(p-methylbenzene-sulphonate) (PTS), 9,9$\sp\prime$-(2,4-hexadiyne-1,6-diyl)-bis-9H-carbazole (DCHD), 1,2-bis((diphenyl-amino)-methyl) -1-buten-3-yne-1,4-diyl (THD), and two form (referred to as A$\sp\prime$ and B) of 5,7-dodecadiyne-1,12-diol-bis(phenyl-carbamate) (TCDU) have been investigated using temperature-dependent reflection and piezomodulated reflection spectroscopy, with primary attention given to results from modulation experiments. Room temperature Raman spectra of TCDU-A$\sp\prime$ and THD have also been measured. Each PDA exhibited unique physical properties that were exploited using piezomodulated reflection (PMR) spectroscopy. Splitting of peaks in the visible spectrum of PTS due to a phase transition at 190 K was examined. PMR spectra show the acetylenic backbone double bond to be the vibrational mode affected first by side group reorientation. The chemically similar side groups in DCHD and THD offer an opportunity to investigate side group induced changes in the electronic energy of the conjugated polymer backbone. Optical spectra exhibited by TCDU-A$\sp\prime$ and $-$ B mimic those of thermochromic or soluble PDA systems, and analysis of low temperatures TCDU spectra finds evidence for intergrowth of A form in B, and vice verse. PMR spectroscopy was used to examine vibronic contributions to the optical electronic spectra of each PDA because of the increased sensitivity and spectral resolution gained compared to unmodulated reflection techniques. Analysis of room temperature PMR spectra show that the electronic transition origin in each PDA is significantly broadened by hot band transitions. PMR spectra measured at low temperature (below 20 K) allow a complete determination of vibronic progressions. In addition, extrema in PMR spectra accurately locate transverse and longitudinal modes for the vibronic bands. Finally, low temperature PMR spectra of PTS, DCHD, and THD display structure that is attributed to a proposed second, close-lying exciton transition.
Subject Area
Chemistry
Recommended Citation
Morrow, Martin Elliot, "Temperature dependent reflection and piezomodulated reflection spectroscopy of polydiacetylene single crystals" (1988). ETD collection for University of Nebraska-Lincoln. AAI8824947.
https://digitalcommons.unl.edu/dissertations/AAI8824947