{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,15]],"date-time":"2026-10-15T08:49:14Z","timestamp":1792054154333,"version":"4.4.0"},"reference-count":65,"publisher":"Wiley","license":[{"start":{"date-parts":[[2026,10,15]],"date-time":"2026-10-15T00:00:00Z","timestamp":1792022400000},"content-version":"vor","delay-in-days":0,"URL":"http:\/\/onlinelibrary.wiley.com\/termsAndConditions#vor"},{"start":{"date-parts":[[2026,10,15]],"date-time":"2026-10-15T00:00:00Z","timestamp":1792022400000},"content-version":"tdm","delay-in-days":0,"URL":"http:\/\/doi.wiley.com\/10.1002\/tdm_license_1.1"}],"content-domain":{"domain":["chemistry-europe.onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["Chemistry A European J"],"abstract":"<jats:title>ABSTRACT<\/jats:title>\n                  <jats:p>\n                    Photoacids are light\u2010responsive molecular systems that convert optical energy into chemical potential through proton release, enabling precise spatiotemporal control of local acidity. Among these, merocyanine\u2013spiropyran (MC\u2013SP) metastable\u2010state photoacids are particularly attractive because photoisomerization is directly coupled to reversible light\u2010driven acid\u2013base switching under mild conditions relevant to chemical and biological systems. Despite significant advances in molecular design, the quantitative relationship between photoisomerization and proton output remains largely unexplored. Here, we systematically investigate four structurally engineered MC\u2013SP photoacids exhibiting distinct switching regimes, ranging from highly reversible to partially irreversible behavior. UV\u2013vis spectroscopic analysis resolves photoisomer populations and switching kinetics, revealing pronounced substituent\u2010dependent effects on electronic structure, photoisomerization dynamics, and photoacidity. To directly quantify proton generation, we developed a spectrally orthogonal near\u2010infrared (NIR)\u2010emissive\n                    <jats:italic>pH probe<\/jats:italic>\n                    that enables real\u2010time, interference\u2010free monitoring of pH changes during continuous photoirradiation. Quantitative analysis of both light\u2010driven MC\u2010to\u2010SP conversion and dark\u2010driven thermal SP\u2010to\u2010MC recovery, combined with fluorescence\u2010based pH measurements, establishes a direct quantitative relationship between molecular photoisomerization, proton release, and proton uptake. This integrated approach establishes a mechanistic link between photoacid structure, photoisomerization dynamics, and proton output, providing design principles for metastable\u2010state photoacids with tunable, light\u2010controlled acidity for chemical and biological applications.\n                  <\/jats:p>","DOI":"10.1002\/chem.71814","type":"journal-article","created":{"date-parts":[[2026,10,15]],"date-time":"2026-10-15T08:26:32Z","timestamp":1792052792000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Quantitative Probing of Photoisomerization\u2010Driven pH Changes in Metastable\u2010State Merocyanine\u2013Spiropyran Photoacids"],"prefix":"10.1002","author":[{"given":"Zakkia","family":"Nizar","sequence":"first","affiliation":[{"name":"Department of Chemistry Indian Institute of Science Education and Research (IISER) Tirupati  Andhra Pradesh India"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0003-2775-059X","authenticated-orcid":false,"given":"Nitish Kumar","family":"Nayak","sequence":"additional","affiliation":[{"name":"Department of Chemistry Indian Institute of Science Education and Research (IISER) Tirupati  Andhra Pradesh India"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2118-8893","authenticated-orcid":false,"given":"Palapuravan","family":"Anees","sequence":"additional","affiliation":[{"name":"Department of Chemistry Indian Institute of Science Education and Research (IISER) Tirupati  Andhra Pradesh India"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"311","published-online":{"date-parts":[[2026,10,15]]},"reference":[{"key":"e_1_2_7_2_1","doi-asserted-by":"publisher","DOI":"10.1039\/c0cp02464c"},{"key":"e_1_2_7_3_1","doi-asserted-by":"publisher","DOI":"10.1039\/d4sc07148d"},{"key":"e_1_2_7_4_1","doi-asserted-by":"publisher","DOI":"10.1021\/ar990109f"},{"key":"e_1_2_7_5_1","doi-asserted-by":"publisher","DOI":"10.1002\/anie.201810118"},{"key":"e_1_2_7_6_1","doi-asserted-by":"crossref","DOI":"10.1002\/9780470594179","volume-title":"Photochemistry and Photophysics of Polymer Materials","author":"Allen N. 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