We report experiments on dendritic molecules with integrated conjugated chromophores that provide microscopic mechanistic information about their solvation dynamics. The fluorescence of a series of immobilized dendritically organized oligothiophenes is studied as they are exposed to good solvents. Initially, the pi-stacking of the oligothiophene units in the dendrimer is destabilized, but full separation of the oligothiophene dendrons takes a time that is orders of magnitude longer due to barriers to torsional motion of the ester linkages. The metastable state prior to separation of the conjugated segments exhibits solution-like spectroscopy but low fluorescence quantum yield relative to the fully solvated segments. This species may play an important role in the photophysics of conjugated oligomer and polymer films. Unusual non-exponential kinetics for the oligothiophene separation step are observed and can be understood in terms of energy transfer among the dendrons.
A highlight of the recent advances in the study of fully functionalized organic photorefractive materials based on polymers, oligomers and small organic molecules is presented.
Photorefractive (PR) materials are multifunctional materials which combine both photoconductivity and electro-optic response to show a new phenomenon: reversible modulation of the index of refraction by light. In the past years, our group has focused on the development of fully functionalized polymers, oligomers and small molecular materials. We have had success in identifying new materials and in gaining understanding in design principles of better materials. Several new PR material systems have been explored, including conjugated PR polymers containing transition metal complexes as photosensitizers, oligothiophene based PR systems and small molecular PR materials containing carbazole and methine dyes. Large net optical gain and minimized phase separation were achieved. The correlation between molecular structure and physical properties is the focal point of this paper.
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