TICT compounds by design: comparison of two naphthalimide-π-dimethylaniline conjugates of different lengths and ground state geometries
Résumé
Two new twisted intramolecular charge transfer (TICT) donor-p-acceptor compounds were designed by
combining a well-known electron acceptor naphthalimide unit with a classic electron donor
dimethylaniline through two types of different rigid linkers. The combined steady-state and timeresolved spectroscopy of molecules in solvents of different polarities in comparison to solid-state
solvation experiments of doped polymer matrixes of different polarities allowed distinguishing between
solvation and conformation determined processes. The photophysical measurements revealed that nonpolar solutions possess high fluorescence quantum yields of up to 70% which is a property of pretwisted/planar molecules in the excited charge transfer (CT) states. The increase of polarity allows tuning
the Stokes shift through all the visible wavelength range up to 8601 cmÿ1 which is accompanied by a
three orders of magnitude drop of fluorescence quantum yields. This is a result of the emerged TICT
states as dimethylaniline twists to a perpendicular position against the naphthalimide core. The TICT
reaction of molecules enables an additional non-radiative excitation decay channel, which is not present
if the twisting is forbidden in a rigid polymer matrix. Transient absorption spectroscopy was employed to
visualize the excited state dynamics and to obtain the excited state reaction constants, revealing that
TICT may occur from both the Franck-Condon region and the solvated pre-twisted/planar CT states.
Both molecules undergo the same photophysical processes, however, a longer linker and thus a higher
excited state dipole moment determines the faster excited state reactions
Domaines
Physique [physics]
Origine : Fichiers produits par l'(les) auteur(s)