Journal
CANADIAN JOURNAL OF CHEMISTRY
Volume 89, Issue 2, Pages 221-234Publisher
CANADIAN SCIENCE PUBLISHING
DOI: 10.1139/V10-102
Keywords
adamantanes; ESIPT; proton transfer; photochemistry; quinone methides; photosolvolysis
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Funding
- National Foundation for Science, Higher Education, and Technological Development (NZZ) [02.05/25]
- Ministry of Science, Education, and Sports of the Republic of Croatia [098-0982933-2911]
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- University of Victoria, Victoria, British Columbia
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2-Phenylphenol derivatives strategically substituted with a hydroxyadamantyl substituent were synthesized and their photochemical reactivity was investigated. Derivatives 9 and 10 undergo competitive excited-state intramolecular proton transfer (ESIPT) from the phenol to the carbon atom of the adjacent phenyl ring and formal ESPT from the phenol to the hydroxyl group coupled with dehydration. These two processes (both via S-1) give rise to two classes of quinone methides (QMs) that revert to starting material or react with nucleophiles, respectively. ESIPT to carbon atoms was studied by performing photolyses in the presence of D2O, whereupon deuterium incorporation to the adjacent phenyl ring was observed (Phi = 0.1-0.2). The competing formal ESPT and dehydration takes place with quantum yields that are an order of magnitude lower and was studied by isolation of photomethanolysis products. Derivative 8 did not undergo ESIPT to carbon atom. Owing to the presence of an intramolecular H bond, an efficient ESIPT from the phenol to the hydroxyl group coupled with dehydration gives a QM that efficiently undergoes electrocyclization (overall Phi = 0.33), to give chroman 16. In addition, spiro[adamantane-2,9'-(4'-hydroxy)fluorene] (12) undergoes ESIPT, unlike the previously reported unreactive parent 2-hydroxyfluorene. The reactive singlet excited states of the prepared biphenyl and fluorene molecules were characterized by fluorescence spectroscopy, whereas laser flash photolysis (LFP) was performed to characterize the longer lived QM intermediates.
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