Kim Kuntze identified three key strategies to enable efficient photoswitching of indigos under red (660 nm) light. They are: (i) choosing a soft polymer matrix to minimise its resistance toward the isomerisation, (ii) creating free volume around the indigo molecules through synthetic modifications, and (iii) applying low dye loading (<1% w/w) to inhibit aggregation. These strategies are shown to improve both photostationary state distributions and the thermal stability of the Z isomer. When all three strategies are implemented, the isomerisation performance (>80% Z form in the photostationary state) is nearly identical to that in the solution.
We also thank our collaborators Dennis Huang (Hokkaido University, Japan) and Stefan Hecht (Humboldt-Universität zu Berlin, Germany).
Read more in the article “Red-light photoswitching of indigos in polymer thin films“.