Continuous Illumination of a Conjugated Polymer Causes Strong Enhancement of Photoluminescence

• Published in: The journal of physical chemistry. B Vol. 125; no. 21; pp. 5636 - 5644
• Main Authors: AlShetwi, Yaser A, Schiefer, Daniel, Sommer, Michael, Reiter, Günter
• Format: Journal Article
• Language: English
• Published: American Chemical Society 03.06.2021
• Subjects: B: Soft Matter, Fluid Interfaces, Colloids, Polymers, and Glassy Materials
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/acs.jpcb.1c01837

We present measurements of absorbance and photoluminescence (PL) for films of poly­(3-(2,5-dioctylphenyl)­thiophene) (PDOPT) as a function of temperature (T) and time (t) of illumination. While having no detectable influence on absorbance of this conjugated polymer, our experiments clearly revealed that illumination of PDOPT caused a significant increase in the PL intensity (I PL(T,t)), that is, the emission probability of PDOPT. Without illumination, we always observed a decrease in I PL with time. An increase in I PL was only detectable when the sample was illuminated. Interestingly, while absorption and emission of photons occur on a time scale of nanoseconds, the here-reported changes in the emission probability were slow and occurred on a time scale of minutes to hours. The influence of illumination on changes in I PL(T,t) was qualitatively similar for slowly and rapidly crystallized PDOPT, that is, the degree of crystallinity was not decisive for the observation. The rate of the increase in I PL depended clearly on the power of the illumination light source. As a function of the illumination time, the change in I PL(T,t) was nonmonotonic and depended on sample temperature. We speculate that changes in polymer interactions caused by excited electronic states might have induced slow changes in polymer conformations.