Supramolecular photochemistry and photophysics. Biacetyl imprisoned in a hemicarcerand

Fernando Pina, A. Jorge Parola, Ester Ferreira, Mauro Maestri, Nicola Armaroli, Roberto Ballardini, Vincenzo Balzani

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41 Citations (Scopus)


When biacetyl is imprisoned into Cram's hemicarcerand 1, its absorption, fluorescence, and phosphorescence maxima are red shifted compared to the values obtained for solutions of free biacetyl in any solvent. Furthermore, the lifetime of the T1 excited state of imprisoned biacetyl is unaffected by solvent nature and presence of dioxygen. These results show that inclusion into the hemicarcerand (i) shields biacetyl from interaction with the solvent molecules and (ii) prevents deactivation of its long-lived T1 excited state by energy transfer to dioxygen. The perturbation provided by the cavity on the spectroscopic properties of biacetyl is much smaller than that provided by even the most "innocent" solvent. The consequent picture is that of a biacetyl molecule which is contained in a not-too-tight cavity where no specific host - guest interaction takes place. The peculiar spectroscopic and excited-state behavior of biacetyl imprisoned in hemicarcerand 1 supports Cram's view that the inner phase of carcerands and hemicarcerands is to be considered as a new phase of matter.

Original languageEnglish
Pages (from-to)12701-12703
Number of pages3
JournalJournal of Physical Chemistry
Issue number34
Publication statusPublished - 1 Jan 1995


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