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Published on: January 16, 2016
Size- and solvent-dependent kinetics for cis-trans isomerization in donor-acceptor systems
Hans-Christian Becker1, Kristine Kilså
1Department of Photochemistry and Molecular Sciences, Box 523, Uppsala University, SE-751 20 Uppsala, Sweden.
Investigating charge transfer compounds revealed that cis-trans isomerization dynamics are influenced by molecular size and solvent viscosity. This conformational change breaks conjugation, affecting rotation time after photoexcitation.
Area of Science:
- Photochemistry
- Molecular Spectroscopy
- Organic Chemistry
Background:
- Charge transfer compounds are crucial in optoelectronic applications.
- Understanding cis-trans isomerization dynamics is key to controlling molecular properties.
Purpose of the Study:
- To investigate cis-trans isomerization dynamics in donor-acceptor compounds.
- To correlate molecular structure and solvent effects with isomerization kinetics.
Main Methods:
- Time-resolved and steady-state optical spectroscopy.
- Systematic variation of donor (dithiafulvene) and acceptor (p-nitrophenyl) moieties.
- Systematic variation of spatial arrangement around an ethynylethene core.
Main Results:
- Compounds exhibit weak fluorescence with a picosecond red-shift.
- Transient absorption spectra blue-shift concurrently with fluorescence red-shift.
- Multi-exponential kinetics correlate with molecular size and solvent viscosity.
Conclusions:
- Photoexcitation breaks conjugation through the central double bond.
- Isomerization time depends on solute-solvent interactions.
- Conformational changes dictate charge transfer dynamics.
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