Electrooptical Absorption Measurements (EOAM) Testify Existence of two Conformers of Prodan and Laurdan with Different Dipole Moments in Equilibrium Ground and Franck-Condon Excited State

• Published in: Journal of fluorescence Vol. 26; no. 5; pp. 1563 - 1572
• Main Authors: Nemkovich, N. A., Detert, H., Roeder, N.
• Format: Journal Article
• Language: English
• Published: New York Springer US 01-09-2016; Springer Nature B.V
• Subjects: Absorption spectra; Analytical Chemistry; Biochemistry; Biological and Medical Physics; Biomedical and Life Sciences; Biomedicine; Biophysics; Biotechnology; Carbonyl groups; Carbonyls; Density functional theory; Dipole moments; Equilibrium; Naphthalene; Original Article; Molecular Stark-effect spectroscopy; Electrooptical absorption measurements (EOAM); Prodan; Laurdan; Dipole moments; Conformers
• ISSN: 1053-0509; 1573-4994
• DOI: 10.1007/s10895-016-1809-0

The results from the electrooptical absorption measurements (EOAM) on the equilibrium ground and excited Franck-Condon state dipole moments of Prodan and Laurdan in 1,4-dioxane are presented. As follows from experiments Prodan and Laurdan in the equilibrium ground and excited Franck-Condon state have two conformers with considerably different dipole moments. The electrical dipole moments and the transition dipole moment, obtained from the short-wavelength region of the absorption spectrum are parallel. The electrical dipole moments measured at the long-wavelength spectral region are parallel to each other but not parallel to the transition dipole moment
m
a
. The angle θ between the transition dipole moment
m
a
and the dipole moment in the equilibrium ground state
μ
g
of the long-wavelength conformer is about 30
0
for both probes. Obtained results evidence that donor-acceptor pairs of the short-wavelength and long-wavelength conformers are not located on the same axis. Two low-energy conformers of Prodan have been found by density functional theory (DFT) calculations, differing in the orientation of the carbonyl group towards the naphthalene system.