Spectroscopic ellipsometry and fluorescence study of thermochromism in an ultrathin poly(diacetylene) film: Reversibility and transition kinetics
The authors have investigated the thermochromic transition of an ultrathin poly(diacetylene)film. The Langmuir film is composed of three layers of polymerized 10,12-pentacosadiynoic acid [Ch{sub 3}(CH{sub 2}){sub 11}C{triple_bond}CC{triple_bond}C(CH{sub 2}){sub 8}COOH] (poly-PCDA) organized into crystalline domains on a silicon substrate. Spectroscopic ellipsometry and fluorescence intensity measurements are obtained with in situ temperature control. Poly-PCDA films exhibit a reversible thermal transition between the initial blue form and an intermediate purple form that exists only at elevated temperature (between 303 and 333 K), followed by an irreversible transition to the red form after annealing above 320 K. The authors propose that the purple form is thermally distorted blue poly-PCDA and may represent a transitional configuration in the irreversible conversion to red. This hypothesis is supported by the appearance of unique features in the absorption spectra for each form as derived from the ellipsometry measurements. Significant fluorescence emission occurs only with the red form and is reduced at elevated temperatures while the absorption remains unchanged. Reduced emission is likely related to thermal fluctuations of the hydrocarbon side chains. Time-resolved fluorescence is likely related to thermal fluctuations of the hydrocarbon side chains. Time-resolved fluorescence measurements of the irreversible transition have been performed. Using a first-order kinetic analysis of these measurements, the authors deduce an energy barrier of 17.6 {+-} 1.1 kcal mol{sup {minus}1} between the blue and red forms.
- Research Organization:
- Sandia National Labs., Albuquerque, NM (US)
- Sponsoring Organization:
- US Department of Energy
- DOE Contract Number:
- AC04-94AL85000
- OSTI ID:
- 20080276
- Journal Information:
- Langmuir, Journal Name: Langmuir Journal Issue: 10 Vol. 16; ISSN LANGD5; ISSN 0743-7463
- Country of Publication:
- United States
- Language:
- English
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