DASA photoswitches work in chloroform if N-methyl
First-generation donor–acceptor Stenhouse adducts with a small N-methyl substituent switch well in chloroform; kinetics split photoisomerisation from cyclisation.
Source
Structure-function relationships of donor-acceptor Stenhouse adduct photochromic switches
Study at a glance
- Design
- Other — Synthesis and photoswitching kinetics/fatigue of DASA photochromes 1–14
- N
- Molecular photochrome SAR — no sample N
- Population
- Donor–acceptor Stenhouse adduct photoswitches
- Outcome
- Photoswitching amplitude, kinetics, and fatigue related to substituents
Structured fields used in claim comparison tables when every cited study has a complete layer.
Inspect source passages
DASA photoswitches work in chloroform if N-methyl
These passages occur verbatim in the stored paper text. They support the points listed below; they do not verify every statement in the explanation.
Most DASAs share λmax = 567 ± 3 nm in chloroform.
Each of these compounds, except 14 , has a similar absorption maximum in chloroform ( λ max = 567 ± 3 nm) indicating the electronic transition responsible for driving the isomerisation is essentially identical for the series.
DASA 1 undergoes a 94% absorbance decrease on irradiation.
shows a typical photoswitching cycle for DASA 1 in chloroform which undergoes a 94% decrease in absorption upon irradiation, followed by rapid equilibration in the dark.
What they did
Authors prepared DASAs 1–14, assigned linear/cyclic isomers by NMR and X-ray, measured photoswitching and 100–1000 cycle fatigue, and fitted a three-species kinetic model.
What they found
Most alkyl-amine DASAs share λmax ≈ 567 nm; DASA 1 drops 94% absorbance on irradiation. N-methyl is needed for good switching; ring-closing rates track substituent parameters. Fatigue can exceed 99% recovery per cycle.
The limits
What it doesn't show
Aqueous switching is not the focus; compound 14 (aniline) behaves differently; air still causes fatigue versus argon.
Key terms
- DASA
- Donor–acceptor Stenhouse adduct: reverse photochrome between a colored triene and a colorless cyclic isomer.
- Photostationary state (PSS)
- Light-on isomer ratio when forward and reverse rates balance.
- Fatigue resistance
- How completely absorbance recovers after repeated light/dark cycles.
- Linear vs cyclic isomer
- Open conjugated triene (colored) versus ring-closed cyclopentenone (pale).
- σ* substituent parameter
- Taft-type electronic parameter used here to predict ring-closing rates.
Flashcards
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Quiz yourself
Good DASA switching in CHCl3 needs:
Common questions
Which amine substituent helps switching?
A small methyl on nitrogen.
Are 1st-generation DASAs useless in CHCl3?
No—several are excellent switches there.
Must both kinetic steps be modelled?
Yes: photoisomerisation and cyclisation rates are comparable.
How robust is DASA 4?
1000 cycles; 50% decomposition only after >610 cycles.
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