Pulsed Laser Spectroscopic Study of the Photoisomerization of Azo Labels at Three Different Locations on a Polystyrene Chain

Chong Sook Paik Sung, Ian R. Gould, Nicholas J. Turro

Research output: Contribution to journalArticlepeer-review

76 Scopus citations


Azobenzene chromophores have been incorporated as molecular labels at three specific sites on a polystyrene chain: the chain end, the chain center, or as the side group. Trans ⇄ cis photoisomerization kinetic behavior of azo labels has been studied both in dilute solution and in the glassy state at 20 °C, using nanosecond pulsed laser spectroscopy, which reduced the measurement time to only 2 s. In dilute solution, a small difference in the label's photoisomerization behavior has been observed at different sites of the chain; the end label can photoisomerize a little faster than the center label or the side label. A much greater difference is observed in the glassy state, especially between the end label and the center label, mainly due to the free volume differences in the vicinity of each label. Assuming that in the glassy state, only a certain fraction of the label can isomerize with the same rate as in dilute solution, only 8% of the center label is found to photoisomerize while about 45% of the chain end or the side group photoisomerizes at 20 °C. The experimental results are discussed in terms of the theoretical predictions based on the free volume size distribution theory of Robertson, which was applied to meet the photoisomerization requirement of the azobenzene label. This theory predicts that 23% of the azo label can isomerize at 20 °C. In view of the packing differences and the resulting free volume differences in the chain end vs. the chain center, the relationships between the theoretical value and the experimental values seem reasonable.

Original languageEnglish (US)
Pages (from-to)1447-1451
Number of pages5
Issue number8
StatePublished - Aug 1984
Externally publishedYes

ASJC Scopus subject areas

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry


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