Photoreaction of indazole metastable-state photoacid

Photochemically‐Driven CO2 Release Using a Metastable‐State Photoacid for Energy Efficient Direct Air Capture

“…If the third cycle of CO 2 release is performed instead only 4 hours after the second cycle, we observed a higher pH increment of 0.31 pH units/hour as shown in Figure S5a. The absorption spectra taken over the course of the reverse reaction process further show clearly that this extended waiting time yielded an equilibrated mixture of slightly different isomer compositions [12, 21, 24] . Nevertheless, our results shown in Figures 3 and S4 confirm that recovery of the trans state occurs simply by ceasing irradiation and this recyclability is ample for subsequent CO 2 release cycles, which can be performed after short periods of equilibration time.…”

“…Since the deprotonation reaction takes place after a series of PSC processes and the resulting neutral and deprotonated isomers are characterized by very different absorption spectra, [11,12,24] this offers a straightforward means to assess the existence of long-lived isomers by simply acquiring absorption spectra of the reaction solutions at different time points during illumination. Figure 2c and d show the absorption spectra acquired for the samples containing 1 mM mPAH and 1 mM KHCO 3 or 1 mM imidazole, respectively, where the trans form is identified as the dominant species prior to illumination (corresponding to numberings 1, 2, and 3).…”

“…Along this line, we report a proof-of-principle study of photochemically-driven CO 2 release by exploiting the unique properties of an indazole metastable-state photoacid (mPAH). [11,12] Our measurements on simulated DAC systems and AA solutions loaded with CO 2 revealed a dramatic pH increase corresponding to the release of CO 2 and concomitant conformational changes of the mPAH with distinct absorption spectra. The resulting CO 2 release was confirmed using NMR spectroscopy, gaseous CO 2 detection, thermogravimetric analysis-mass spectrometry (TGA-MS), and total inorganic carbon analysis, with quantification of � 55 % and � 68 % to � 78 % conversion of the total inorganic carbon to CO 2 in the simulated and AA-based DAC systems, respectively.…”

“…Along this line, we report a proof‐of‐principle study of photochemically‐driven CO 2 release by exploiting the unique properties of an indazole metastable‐state photoacid (mPAH) [11, 12] . Our measurements on simulated DAC systems and AA solutions loaded with CO 2 revealed a dramatic pH increase corresponding to the release of CO 2 and concomitant conformational changes of the mPAH with distinct absorption spectra.…”

“…Photoacids are known to dramatically lower their pK aand therefore the solution pH-upon optical excitation with either UV or visible light. [12][13][14] This offers an attractive means to photochemically drive efficient release of the CO 2 through a deliberate proton transfer reaction using light from the sun. The concept of our DAC approach based on an AA sorbent and a mPAH driven photochemical release of CO 2 is depicted in Figure 1.…”