INFLUENCE OF CYANO SUBSTITUENTS ON THE EFFECTIVE S1 TORSIONAL POTENTIALS OF SYMMETRICAL AND SYMMETRY-DISTURBED DERIVATIVES OF 9,9'-BIANTHRYL IN CONDENSED MEDIA
K. Elich et al., INFLUENCE OF CYANO SUBSTITUENTS ON THE EFFECTIVE S1 TORSIONAL POTENTIALS OF SYMMETRICAL AND SYMMETRY-DISTURBED DERIVATIVES OF 9,9'-BIANTHRYL IN CONDENSED MEDIA, Journal of physical chemistry, 97(39), 1993, pp. 9947-9955
Optical fluorescence spectra of 9-cyanoanthracene (9CA), 10-cyano-9,9'
-bianthryl (CBA), and 10, 10'-dicyano-9,9'-bianthryl (DCB) in 2-methyl
butane (2MB) were measured at several temperatures between 120 and 298
K. The 9CA spectra were subjected to a Franck-Condon (FC) analysis ba
sed upon a two-state model with eleven normal modes. On the basis of t
hese results a simultaneous FC and band-shape analysis of the temperat
ure-dependent spectra was carried out for CBA and DCB to determine the
effective S1 torsional potential. The S1 double-minimum torsional pot
ential of the symmetrical derivative DCB in 2MB has a local barrier at
phi = 90-degrees of DELTAV = 290 cm-1, very similar to 9,9'-bianthryl
(BA). On the other hand, a strong increase of the local barrier (DELT
AV= 680 cm-1) can be deduced for the symmetry-disturbed derivative CBA
from the model calculations. The minimum angle phi(min) was found to
be 63-degrees and 62-degrees for DCB and CBA, respectively. The fluore
scence quantum yields and lifetimes were determined for BA, CBA, and D
CB in apolar solvents. The comparison of the calculated radiative tran
sition rates (estimated from absorption spectra) with the experimental
values confirms the validity of the Condon approximation. No evidence
for an emission from a charge-transfer (CT) state could be found for
CBA and DCB in 2MB.