The Photophysical Behavior of Ester-Substituted Aminocoumarins: A New Twist
Abstract
The fluorescent behavior of two amino-substituted coumarin esters was examined in solvents of different polarity. Coumarin 3, a simple ester derivative, behaves conventionally. Its fluorescence emission shifts to lower energy as the solvent polarity increases and the efficiency of the emission is essentially unaffected by solvent change. This behavior is characteristic of a rotation-inhibited intramolecular charge transfer (ICT) state. Coumarin 4, substituted with an alpha-keto ester function at the 3-position, also shows emission characteristic of an ICT state. However, in this case, the fluorescence efficiency and lifetime of the excited state decrease markedly as the solvent polarity increases. This behavior is characteristic of formation of a non- emissive twisted intramolecular charge transfer (TICT) state. Since rotation of 4 about the carbon-nitrogen bond is inhibited, twisting must occur around another group in the molecule. Consideration of the structure leads to identification of a rotation around the bond connecting the carbonyl group of 4 as leading to a TICT state. Keywords: Twisted charge transfer, Amino compounds.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 06, 1988
- Accession Number
- ADA196979
Entities
People
- Gary Schuster
- J. A. Van Gompel
Organizations
- University of Illinois Urbana–Champaign