{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,9]],"date-time":"2026-03-09T22:55:03Z","timestamp":1773096903688,"version":"3.50.1"},"reference-count":52,"publisher":"AIP Publishing","issue":"10","funder":[{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["JP22K05253"],"award-info":[{"award-number":["JP22K05253"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["JP23K23425"],"award-info":[{"award-number":["JP23K23425"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["JP24K23082"],"award-info":[{"award-number":["JP24K23082"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100002241","name":"Japan Science and Technology Agency","doi-asserted-by":"publisher","award":["JPMJSP2110"],"award-info":[{"award-number":["JPMJSP2110"]}],"id":[{"id":"10.13039\/501100002241","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["pubs.aip.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,3,14]]},"abstract":"<jats:p>We theoretically investigated vibronic coupling responsible for nonradiative transitions, i.e., internal conversion (IC) and intersystem crossing (ISC), in xanthone. The nonradiative decay pathway of aromatic ketones is often debated because of their fast ISC. Xanthone in the gas phase follows a pathway that obeys El-Sayed\u2019s rule, namely, IC from the 1\u03c0\u03c0* to 1n\u03c0* states and ISC from the 1n\u03c0* to 3\u03c0\u03c0* states, of which a simple pathway is adequate for analyzing vibronic structures. We employed an expression for the nonradiative rate constant based on Fermi\u2019s golden rule within the mixed-spin crude adiabatic approximation, which has the advantage that both IC and ISC can be considered as equally vibronically induced transitions. Our calculations showed that the IC from the 1\u03c0\u03c0* to 1n\u03c0* state was faster than ISC channels because of stronger vibronic coupling and less favorable spin\u2013orbit (SO) coupling to nearby triplets. In addition, the ISC from 1n\u03c0* to 3\u03c0\u03c0* was faster than that from 1n\u03c0* to 3n\u03c0* because of the large structural displacement and small energy gap. This study can provide guidelines for determining whether IC or ISC dominates, depending on the balance between vibronic coupling, SO coupling, and the energy gap, thereby informing molecular design for controlled nonradiative decay. ISC can dominate its IC counterpart in a xanthone derivative by tuning the singlet\u2013triplet energy gap and\/or the SO coupling.<\/jats:p>","DOI":"10.1063\/5.0314647","type":"journal-article","created":{"date-parts":[[2026,3,9]],"date-time":"2026-03-09T12:36:05Z","timestamp":1773059765000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Vibronic coupling of competing internal conversion and intersystem crossing in xanthone"],"prefix":"10.1063","volume":"164","author":[{"given":"Takeaki","family":"Zaima","sequence":"first","affiliation":[{"name":"Fukui Institute for Fundamental Chemistry, Kyoto University 1 , Takano Nishibiraki-cho 34-4, Sakyo-ku, Kyoto 606-8103,","place":["Japan"]},{"name":"Department of Molecular Engineering, Graduate School of Engineering, Kyoto University 2 , Nishikyo-ku, Kyoto 615-8510,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8044-487X","authenticated-orcid":false,"given":"Wataru","family":"Ota","sequence":"additional","affiliation":[{"name":"Fukui Institute for Fundamental Chemistry, Kyoto University 1 , Takano Nishibiraki-cho 34-4, Sakyo-ku, Kyoto 606-8103,","place":["Japan"]},{"name":"Department of Molecular Engineering, Graduate School of Engineering, Kyoto University 2 , Nishikyo-ku, Kyoto 615-8510,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0032-8535","authenticated-orcid":false,"given":"Tatsuhisa","family":"Kato","sequence":"additional","affiliation":[{"name":"Fukui Institute for Fundamental Chemistry, Kyoto University 1 , Takano Nishibiraki-cho 34-4, Sakyo-ku, Kyoto 606-8103,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-4554-8411","authenticated-orcid":false,"given":"Tohru","family":"Sato","sequence":"additional","affiliation":[{"name":"Fukui Institute for Fundamental Chemistry, Kyoto University 1 , Takano Nishibiraki-cho 34-4, Sakyo-ku, Kyoto 606-8103,","place":["Japan"]},{"name":"Department of Molecular Engineering, Graduate School of Engineering, Kyoto University 2 , Nishikyo-ku, Kyoto 615-8510,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"317","published-online":{"date-parts":[[2026,3,9]]},"reference":[{"key":"2026030908355533800_c1","volume-title":"Principles of Molecular Photochemistry: An Introduction","year":"2009"},{"key":"2026030908355533800_c2","doi-asserted-by":"publisher","first-page":"715","DOI":"10.1063\/1.1668703","article-title":"Intramolecular radiationless transitions","volume":"48","year":"1968","journal-title":"J.\u00a0Chem. 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