Yucknovsky Anna, Rich Benjamin B, Gutkin Sara, Ramanthrikkovil Variyam Ambili, Shabat Doron, Pokroy Boaz, Amdursky Nadav
Schulich Faculty of Chemistry, Technion─Israel Institute of Technology, Haifa 3200003, Israel.
Department of Materials Science & Engineering, Technion─Israel Institute of Technology, Haifa 3200003, Israel.
J Phys Chem B. 2022 Aug 25;126(33):6331-6337. doi: 10.1021/acs.jpcb.2c04020. Epub 2022 Aug 12.
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 p of -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 p of ∼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.
pH响应系统的动态控制是许多自然和人工过程的核心。在这里，我们使用光酸，即仅在激发态解离并将质子转移到附近质子受体的分子，来实现过程的动态控制。当需要使高酸性受体质子化时，就会出现一个问题。我们使用激发态pKa为-8的超强光酸来解决这个问题，从而使它们能够使非常弱的质子受体质子化。我们所针对的过程是液滴的光触发自推进，它由激发态质子转移（ESPT）引发，即从超强光酸供体转移到位于液滴表面、pKa约为0的表面活性剂受体。我们首先使用稳态和时间分辨光谱证实，超强光酸可以对酸性表面活性剂进行ESPT，而“普通”光酸则不能。接下来，我们展示了在照射溶剂化的超强光酸时液滴的自推进。我们还通过瞬态表面张力测量进一步证实了液滴表面表面活性剂的质子化。我们的系统是应用超强光酸控制动态过程的首个实例，并为光触发动态系统领域开辟了新的可能性。
