DASA photoswitches work in chloroform if N-methyl

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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

Mallo N, Foley ED, Iranmanesh H, et al. · Chemical science · 2018

doi.org/10.1039/c8sc03218a Read the full paper ↗69 citationscc by

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.

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.

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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.