Application of Super Photoacids in Controlling Dynamic Processes: Light-Triggering the Self-Propulsion of Oil Droplets

Anna Yucknovsky, Benjamin B. Rich, Sara Gutkin, Ambili Ramanthrikkovil Variyam, Doron Shabat, Boaz Pokroy, Nadav Amdursky*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


The dynamic control of pH-responsive systems is at the heart of many natural and artificial processes. Here, we use photoacids, molecules that dissociate only in their excited state and transfer their proton to nearby proton acceptors, for the dynamic control of processes. A problem arises when there is a need to protonate highly acidic acceptors. We solve this problem using super photoacids that have an excited-state pKaof -8, thus enabling them to protonate very weak proton acceptors. The process that we target is the light-triggered self-propulsion of droplets, initiated by an excited-state proton transfer (ESPT) from a super photoacid donor to a surfactant acceptor situated on the surface of the droplet with a pKaof ∼0. We first confirm using steady-state and time-resolved spectroscopy that a super photoacid can undergo ESPT to the acidic surfactant, whereas a "regular" photoacid cannot. Next, we show self-propulsion of the droplet upon irradiating the solvated super photoacid. We further confirm the protonation of the surfactant on the surface of the droplet using transient surface tension measurements. Our system is the first example of the application of super photoacids to control dynamic processes and opens new possibilities in the field of light-triggered dynamic systems.

Original languageEnglish
Pages (from-to)6331-6337
Number of pages7
JournalJournal of Physical Chemistry B
Issue number33
StatePublished - 25 Aug 2022


FundersFunder number
Ariane de Rothschild
United States-Israel Binational Science Foundation2018239
Ministry of Science and Technology, Israel3-16243


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