Bimanes. 22. Flexible fluorescent molecules. Solvent effects on the photophysical properties of syn-bimanes (1,5-diazabicyclo[3.3.0]octa-3,6-diene-2,8-diones)

Edward M. Kosower*, Rina Giniger, Annette Radkowsky, David Hebel, Alan Shusterman

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

42 Scopus citations

Abstract

The photophysical properties of bimanes (1,5-diazabicyclo[3.3.0]octa-3,6-diene-2,8-diones) exhibit two types of behavior in solution. The maximal absorption energies, the maximal emission energies, the quantum yields of fluorescence, and the radiative rate constants all decrease (a) moderately fast with solvent polarities up to the intermediate range and (b) slowly from the intermediate polarity range up to water. The bimanes examined include syn-(hydro,hydro)bimane (1), syn-(methyl, fluoro)bimane (2), syn-(methyl,hydro)bimane (3), μ(0)-syn-(methylene,methyl)bimane (4), syn-(methyl,chloro)bimane (5), and syn-(methyl,methyl)bimane (6). The effects are interpreted in terms of two conformational isomers, "bent" and "quasi-planar", for both the ground and excited states. The magnitude of the solvent sensitivities of the photophysical properties, the nature of the conjugation, and the shapes observed in crystal structures suggest that solvent polarity affects the conformation of the bent conformers. The equilibrium between bent and quasi-planar forms may not vary much with solvent polarity, but the appearance of the emission spectrum changes drastically due to substantial differences in the radiative rates for the two conformers.

Original languageEnglish
Pages (from-to)5552-5557
Number of pages6
JournalJournal of Physical Chemistry
Volume90
Issue number22
DOIs
StatePublished - 1986

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