A Reversible Photoacid Switched by Different Wavelengths of Light

Abstract

Reversible photoacids have been widely used in different areas for control of proton-driven processes with light. Previously reported reversible photoacids rely on thermal relaxation to return to the low-acidity ground state. Herein we report a photoacid that can be switched between low-acidity and highacidity states by different wavelengths of light. The photoacid can be converted into a high-acidity metastable state by 470 nm irradiation. The thermal relaxation of the metastable state is very slow and its half-life in DMSO is 55 h. Irradiation with 365 nm light quickly induced the reverse reaction and reached a photostationary state. UV/Vis absorption spectra of the forward and reverse processes induced by 470 nm and 365 nm irradiation, respectively, have well-matched isosbestic points. No decomposition was observed after the photoacid was switched by the two wavelengths of light for many cycles. Reversible patterning with both writing and erasing steps performed with light was demonstrated using a polymer thin film containing the photoacid and chlorophenol red as the proton acceptor.

Reversible photo control of proton chemistry

“…5 The photo p K a of merocyanine mPAH is 2–3 in water, 7,8 which is lower than that of indazole mPAH (4–6). 5,53 So the merocyanine mPAH is suitable for creating a large [H + ] but cannot be used under basic conditions. In fact, a pH change of 2–3 units has been routinely produced by merocyanine mPAHs.…”

“…44,45 Recently, our group reported an indazole mPAH, which has a very slow thermal reverse reaction. 53 However, the reverse reaction can be quickly induced by a different wavelength (365 nm) from that of the forward reaction (470 nm). Such a photoacid allows both high [H + ] and fast switching.…”

“…44,45 Our group demonstrated a polymer photochromic material, which can be patterned and erased using different wavelengths of light. 53 The mPAH used in this material was the photoswitchable indazole mPAH described in the previous section. Photoresponsive molecular systems are essential for molecular optoelectronic devices.…”

Arylazo Sulfones as Nonionic Visible-Light Photoacid Generators

“…Nevertheless, there is an interest in the development of visible-light PAGs for applications in 3D printing systems, photocurable adhesives, and incorporation in photoresists sensitive to 436 nm light (the so-called g-line 25 ). Visible-absorbing sulfonium salts 26 BODIPY 27 and especially photochromic-based derivatives 28 have been devised accordingly. As part of our ongoing interest in the applications of colored dyedauxiliary-group-bearing molecules, we focused on arylazo sulfones 29 ( VI , Scheme 1 path c) as visible-light-active PAGs.…”

Solvation-Tuned Photoacid as a Stable Light-Driven pH Switch for CO2 Capture and Release

“…Recently, there has been a growing interest in employing photoacids for CO 2 capture applications. − This approach harnesses a photodriven pH change, offering an attractive alternative to the energy-intensive pressure and temperature swings that are traditionally used for sorbent regeneration . In the process that employs photoacids, CO 2 is first captured by an alkaline solution (sorbent) containing protonated photoacid, leading to the formation of bicarbonate (HCO 3 – ). − Next, to regenerate, the sorbent solution is exposed to light, triggering the release of protons followed by bicarbonate protonation, which in turn releases gaseous CO 2 .…”