Electronic spectroscopy and photoisomerization of trans-urocanic acid in a supersonic jet

W.L. Ryan, D.H. Levy

Research output: Contribution to journalArticlepeer-review

35 Scopus citations


trans-Urocanic acid (trans-UA), a component of the epidermal layer of skin, exhibits wavelength-dependent photochemistry. The quantum efficiency of isomerization to cis-UA is greatest when the molecule is excited on the long wavelength tail of its absorption profile in solution (300-320 nm). However, exciting the molecule where it absorbs UV light most efficiently (260-285 nm) causes almost no isomerization. We have used fluorescence excitation and dispersed emission methods in a supersonic jet to investigate the electronic states involved in this complex and interesting photochemistry. Three distinct regions are present in the excitation spectrum. Region I, which is below the isomerization barrier, contains sharp, well-resolved peaks that upon excitation emit from the S(1) state of trans-UA. Region II exhibits peaks that increase in broadness and decrease in intensity with increasing excitation energy. Upon excitation these peaks produce dual emission from the S(1) states of both trans- and cis-UA. The trans to cis isomerization barrier is estimated to be 1400 cm(-1). Region III exhibits excitation to the S(2) electronic state and has a broad structure that spans 3000 cm(-1) and occurs 4000 cm(-1) above S(1). S(2) excitation results in essentially no trans to cis isomerization.

Original languageEnglish (US)
Pages (from-to)961-6
Number of pages6
JournalJournal of the American Chemical Society
Issue number5
StatePublished - Feb 7 2001


  • Aircraft
  • Isomerism
  • Photochemistry
  • Spectrophotometry, Ultraviolet
  • Urocanic Acid/chemistry

PubMed: MeSH publication types

  • Journal Article


Dive into the research topics of 'Electronic spectroscopy and photoisomerization of trans-urocanic acid in a supersonic jet'. Together they form a unique fingerprint.

Cite this