On the barrier to excited-state intramolecular proton transfer (ESIPT): The controversial assignment of the spectra of 2,5-bis(2-benzoxazolyl)hydroquinone in solid argon

✍ Scribed by Bernhard Dick

• Publisher: Elsevier Science
• Year: 1989
• Tongue: English
• Weight: 733 KB
• Volume: 158
• Category: Article
• ISSN: 0009-2614
• DOI: 10.1016/0009-2614(89)87290-2

✦ Synopsis

The spectra of 2,5-bis( 2-benzoxazolyl)hydroquinone (BBXHQ) in solid argon at IS K reveals two species. The major species (96%) undergoes very efficient excited-state intramolecular proton transfer (ESIPT) after excitation to S,. It is assigned to the isolated BBXHQ molecule (solvated by argon atoms) in which ESIPT is not thermally activated. Either no energy barrier exists or it can be overcome by proton tunneling with a rate constant greater than 8x IO" s-'. The minor species produces only fluorescence with a normal Stokes shift, indicating the absence of ESIPT. It is tentatively assigned to a dimer of BBXHQ.