title: Origin of the Reversible Thermochromic Properties of Polydiacetylenes Revealed by Ultrafast Spectroscopy.
abstract: Polydiacetylenes (PDAs) with thermochromic properties undergo colorimetric transitions when the external temperature is varied. This capability has the potential to enable these materials to be used as temperature sensors. These thermochromic properties of PDAs stem from their temperature-dependent optical properties. In this work, we studied the temperature-dependent optical properties of Bis-PDA-Ph, which exhibits reversible thermochromic properties, and PCDA-PDA, which exhibits irreversible thermochromic properties, by UV-visible absorption and femtosecond transient absorption spectroscopy. Our results indicate that the electronic relaxation of PDAs occurs via an intermediate state in cases where the material exhibits reversible thermochromic properties, whereas the excited PDAs relax directly back to the ground state when irreversible thermochromic properties are observed. The existence of this intermediate state in the electronic relaxation of PDAs thus plays an important role in determining their thermochromic properties. These results are very important for both understanding and strategically modulating the thermochromic properties of PDAs.
authors.affiliation: Department of Chemistry, Korea University , Seoul 136-701, Korea.
authors.forename: Junwoo
authors.initials: J
authors.lastname: Baek
authors.affiliation: Department of Chemistry, Korea University , Seoul 136-701, Korea.
authors.forename: Joonyoung F
authors.initials: JF
authors.lastname: Joung
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul, 120-750, Korea.
authors.forename: Songyi
authors.initials: S
authors.lastname: Lee
authors.affiliation: Space-Time Resolved Molecular Imaging Research Team, Korea Basic Science Institute , Seoul 136-713, Korea.
authors.forename: Hanju
authors.initials: H
authors.lastname: Rhee
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul, 120-750, Korea.
authors.forename: Myung Hwa
authors.initials: MH
authors.lastname: Kim
authors.affiliation: Department of Chemistry, Korea University , Seoul 136-701, Korea.
authors.forename: Sungnam
authors.initials: S
authors.lastname: Park
authors.affiliation: Department of Chemistry and Nano Science, Ewha Womans University , Seoul, 120-750, Korea.
authors.forename: Juyoung
authors.initials: J
authors.lastname: Yoon