title: Relationship between the molecular structure of cyanine dyes and the vibrational fine structure of their electronic absorption spectra.
abstract: Electronic absorption spectra of symmetrical cyanine dyes show vibronic sub-bands, attributed to the symmetric C-C valence vibration of the polymethine chain in the electronic excited state. Displacements in the equilibrium configuration between electronic ground and excited states of cyanine dyes lead to longer C-C bonds in the excited state. Additionally, in the electronic ground state, a small degree of bond localisation always remains in the chain depending on the different heterocyclic terminal groups. Our investigations suggest that we can use (3)J(H,H) coupling constants in the polymethine chain to characterise the bond localisation within the chain. Based on these values and the Franck-Condon principle, the intensity distribution among the vibrational sub-bands can be explained.
authors.affiliation: FEW Chemicals GmbH, Technikumstrasse 1, 06756 Bitterfeld-Wolfen, Germany. mustroph@few.de
authors.forename: Heinz
authors.initials: H
authors.lastname: Mustroph
authors.forename: Knut
authors.initials: K
authors.lastname: Reiner
authors.forename: Jürgen
authors.initials: J
authors.lastname: Mistol
authors.forename: Steffen
authors.initials: S
authors.lastname: Ernst
authors.forename: Dietmar
authors.initials: D
authors.lastname: Keil
authors.forename: Lothar
authors.initials: L
authors.lastname: Hennig