{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T13:06:38Z","timestamp":1788872798635,"version":"build-2803163510"},"reference-count":38,"publisher":"AIP Publishing","issue":"10","funder":[{"DOI":"10.13039\/501100001691","name":"Japan Society for the Promotion of Science","doi-asserted-by":"publisher","award":["JP20H05838"],"award-info":[{"award-number":["JP20H05838"]}],"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":["JP25H01674"],"award-info":[{"award-number":["JP25H01674"]}],"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":["JP24H00485"],"award-info":[{"award-number":["JP24H00485"]}],"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":["JP24K21809"],"award-info":[{"award-number":["JP24K21809"]}],"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":["JPJS00420230010"],"award-info":[{"award-number":["JPJS00420230010"]}],"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":["JP20H05837"],"award-info":[{"award-number":["JP20H05837"]}],"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":["JP26H00372"],"award-info":[{"award-number":["JP26H00372"]}],"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":["JP20H05840"],"award-info":[{"award-number":["JP20H05840"]}],"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":["JP26H02293"],"award-info":[{"award-number":["JP26H02293"]}],"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":["JPJSCCA20220004"],"award-info":[{"award-number":["JPJSCCA20220004"]}],"id":[{"id":"10.13039\/501100001691","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100003382","name":"Core Research for Evolutional Science and Technology","doi-asserted-by":"publisher","award":["JPMJCR2431"],"award-info":[{"award-number":["JPMJCR2431"]}],"id":[{"id":"10.13039\/501100003382","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["pubs.aip.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,9,14]]},"abstract":"<jats:p>The photophysical properties of the para-connected MA-TA and meta-connected mMA-TA donor\u2013acceptor thermally activated delayed fluoresence (TADF) structural isomers were investigated to clarify how substitution patterns affect excited-state relaxation dynamics in TADF molecules. Time-resolved photoluminescence measurements showed that MA-TA exhibits relatively simple emissive-state relaxation, whereas mMA-TA shows a time-dependent red shift of the emission band and biexponential photoluminescence decay. Using reference spectra obtained from steady-state absorption and fragment transient absorption measurements, femtosecond transient absorption spectroscopy revealed that MA-TA undergoes rapid formation of a charge-transfer-like excited state within several picoseconds, as indicated by the decay of a broad MA-like near-infrared excited-state absorption component monitored around 850\u00a0nm and the concomitant rise of a CT-like excited-state absorption around 600\u00a0nm. In contrast, mMA-TA exhibited a spectroscopic signature of an additional intermediate excited-state species, observed as a transient absorption band around 700\u00a0nm, that was not clearly observed for MA-TA. The delayed appearance and relatively fast decay of this signal indicate that mMA-TA forms an intermediate excited-state species during early relaxation. These results demonstrate that the substitution pattern strongly influences the early excited-state relaxation pathway in these TADF molecules. The formation of an additional intermediate excited-state species in mMA-TA may provide a plausible origin for its more complex photoluminescence dynamics and lower emission efficiency. This study highlights the importance of controlling substitution-dependent intermediate excited-state formation in the molecular design of efficient TADF emitters.<\/jats:p>","DOI":"10.1063\/5.0350251","type":"journal-article","created":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T12:07:59Z","timestamp":1788869279000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Substitution-dependent excited-state relaxation pathways in the TADF structural isomers MA-TA and mMA-TA"],"prefix":"10.1063","volume":"165","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-9977-7439","authenticated-orcid":false,"given":"Kosaku","family":"Kato","sequence":"first","affiliation":[{"name":"Graduate School of Natural Science and Technology, Okayama University 1 , 3-1-1, Tsushima-naka, Kita-ku, Okayama 700-8530,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8042-9517","authenticated-orcid":false,"given":"Katsuaki","family":"Suzuki","sequence":"additional","affiliation":[{"name":"Institute for Chemical Research, Kyoto University Uji 2 , Kyoto 611-0011,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5111-3852","authenticated-orcid":false,"given":"Hironori","family":"Kaji","sequence":"additional","affiliation":[{"name":"Institute for Chemical Research, Kyoto University Uji 2 , Kyoto 611-0011,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3179-7588","authenticated-orcid":false,"given":"Akira","family":"Yamakata","sequence":"additional","affiliation":[{"name":"Graduate School of Natural Science and Technology, Okayama University 1 , 3-1-1, Tsushima-naka, Kita-ku, Okayama 700-8530,","place":["Japan"]},{"name":"Research Institute of Interdisciplinary Science, Okayama University 3 , 3-1-1, Tsushima-naka, Kita-ku, 700-8530 Okayama,","place":["Japan"]},{"name":"Institute for Aqua Regeneration (ARG), Shinshu University 4 , 4-17-1 Wakasato, Nagano-Shi, Nagano 380-8553,","place":["Japan"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"317","published-online":{"date-parts":[[2026,9,8]]},"reference":[{"key":"2026090808075462000_c1","doi-asserted-by":"publisher","first-page":"657","DOI":"10.3389\/fchem.2020.00657","article-title":"High triplet energy host materials for blue TADF OLEDs-A tool box approach","volume":"8","year":"2020","journal-title":"Front. Chem."},{"key":"2026090808075462000_c2","doi-asserted-by":"publisher","first-page":"4802","DOI":"10.1002\/adma.200900983","article-title":"Thermally activated delayed fluorescence from Sn4+-porphyrin complexes and their application to organic light-emitting diodes\u2014A novel mechanism for electroluminescence","volume":"21","year":"2009","journal-title":"Adv. Mater."},{"key":"2026090808075462000_c3","doi-asserted-by":"publisher","first-page":"8476","DOI":"10.1038\/ncomms9476","article-title":"Purely organic electroluminescent material realizing 100% conversion from electricity to light","volume":"6","year":"2015","journal-title":"Nat. Commun."},{"key":"2026090808075462000_c4","doi-asserted-by":"publisher","first-page":"253","DOI":"10.1038\/nphoton.2012.31","article-title":"Organic light-emitting diodes employing efficient reverse intersystem crossing for triplet-to-singlet state conversion","volume":"6","year":"2012","journal-title":"Nat. Photonics"},{"key":"2026090808075462000_c5","doi-asserted-by":"publisher","first-page":"234","DOI":"10.1038\/nature11687","article-title":"Highly efficient organic light-emitting diodes from delayed fluorescence","volume":"492","year":"2012","journal-title":"Nature"},{"key":"2026090808075462000_c6","doi-asserted-by":"publisher","first-page":"11392","DOI":"10.1039\/c2cc36237f","article-title":"Efficient green thermally activated delayed fluorescence (TADF) from a phenoxazine-triphenyltriazine (PXZ-TRZ) derivative","volume":"48","year":"2012","journal-title":"Chem. Commun."},{"key":"2026090808075462000_c7","doi-asserted-by":"publisher","first-page":"3766","DOI":"10.1021\/cm402428a","article-title":"Twisted intramolecular charge transfer state for long-wavelength thermally activated delayed fluorescence","volume":"25","year":"2013","journal-title":"Chem. Mater."},{"key":"2026090808075462000_c8","doi-asserted-by":"publisher","first-page":"13680","DOI":"10.1038\/ncomms13680","article-title":"Revealing the spin-vibronic coupling mechanism of thermally activated delayed fluorescence","volume":"7","year":"2016","journal-title":"Nat. Commun."},{"key":"2026090808075462000_c9","doi-asserted-by":"publisher","first-page":"012001","DOI":"10.1088\/2050-6120\/aa537e","article-title":"Photophysics of thermally activated delayed fluorescence molecules","volume":"5","year":"2017","journal-title":"Methods Appl. Fluoresc."},{"key":"2026090808075462000_c10","doi-asserted-by":"publisher","first-page":"e1603282","DOI":"10.1126\/sciadv.1603282","article-title":"Evidence and mechanism of efficient thermally activated delayed fluorescence promoted by delocalized excited states","volume":"3","year":"2017","journal-title":"Sci. Adv."},{"key":"2026090808075462000_c11","doi-asserted-by":"publisher","first-page":"eaao6910","DOI":"10.1126\/sciadv.aao6910","article-title":"Excited state engineering for efficient reverse intersystem crossing","volume":"4","year":"2018","journal-title":"Sci. Adv."},{"key":"2026090808075462000_c12","doi-asserted-by":"publisher","first-page":"23190","DOI":"10.1021\/acsami.6b05877","article-title":"Ideal molecular design of blue thermally activated delayed fluorescent emitter for high efficiency, small singlet-triplet energy splitting, low efficiency roll-off, and long lifetime","volume":"8","year":"2016","journal-title":"ACS Appl. Mater. Interfaces"},{"key":"2026090808075462000_c13","doi-asserted-by":"publisher","first-page":"1705641","DOI":"10.1002\/adma.201705641","article-title":"Adamantyl substitution strategy for realizing solution-processable thermally stable deep-blue thermally activated delayed fluorescence materials","volume":"30","year":"2018","journal-title":"Adv. Mater."},{"key":"2026090808075462000_c14","doi-asserted-by":"publisher","first-page":"14706","DOI":"10.1021\/ja306538w","article-title":"Design of efficient thermally activated delayed fluorescence materials for pure blue organic light emitting diodes","volume":"134","year":"2012","journal-title":"J.\u00a0Am. Chem. Soc."},{"key":"2026090808075462000_c15","doi-asserted-by":"publisher","first-page":"2096","DOI":"10.1002\/adma.201405474","article-title":"Nearly 100% internal quantum efficiency in undoped electroluminescent devices employing pure organic emitters","volume":"27","year":"2015","journal-title":"Adv. Mater."},{"key":"2026090808075462000_c16","doi-asserted-by":"publisher","first-page":"1600080","DOI":"10.1002\/advs.201600080","article-title":"The role of local triplet excited states and D-A relative orientation in thermally activated delayed fluorescence: Photophysics and devices","volume":"3","year":"2016","journal-title":"Adv. Sci."},{"key":"2026090808075462000_c17","doi-asserted-by":"publisher","first-page":"2764","DOI":"10.1021\/acs.jpclett.2c03925","article-title":"Donor, acceptor, and molecular charge transfer emission all in one molecule","volume":"14","year":"2023","journal-title":"J.\u00a0Phys. Chem. Lett."},{"key":"2026090808075462000_c18","doi-asserted-by":"publisher","first-page":"1490","DOI":"10.1246\/cl.170587","article-title":"Molecular design for blue thermal activated delayed fluorescence materials: Substitution position effect","volume":"46","year":"2017","journal-title":"Chem. Lett."},{"key":"2026090808075462000_c19","doi-asserted-by":"publisher","first-page":"21883","DOI":"10.1039\/d1cp03144a","article-title":"Highly efficient T-shaped deep-red thermally activated delayed fluorescence emitters: Substitution position effect","volume":"23","year":"2021","journal-title":"Phys. Chem. Chem. Phys."},{"key":"2026090808075462000_c20","doi-asserted-by":"publisher","first-page":"5813","DOI":"10.1039\/d2tc00212d","article-title":"Efficient thermally activated delayed fluorescence emitters based on a parallelly aligned bi-spiro-acridine donor","volume":"10","year":"2022","journal-title":"J.\u00a0Mater. Chem. C"},{"key":"2026090808075462000_c21","doi-asserted-by":"publisher","first-page":"23618","DOI":"10.1021\/acs.jpcc.7b08034","article-title":"Impact of donor substitution pattern on the TADF properties in the carbazolyl-substituted triazine derivatives","volume":"121","year":"2017","journal-title":"J.\u00a0Phys. Chem. C"},{"key":"2026090808075462000_c22","doi-asserted-by":"publisher","first-page":"9184","DOI":"10.1039\/c9tc02742d","article-title":"Revealing resonance effects and intramolecular dipole interactions in the positional isomers of benzonitrile-core thermally activated delayed fluorescence materials","volume":"7","year":"2019","journal-title":"J.\u00a0Mater. Chem. C"},{"key":"2026090808075462000_c23","doi-asserted-by":"publisher","first-page":"108","DOI":"10.3169\/mta.3.108","article-title":"Meta-linking strategy for thermally activated delayed fluorescence emitters with a small singlet-triplet energy gap","volume":"3","year":"2015","journal-title":"ITE Trans. Media Technol. Appl."},{"key":"2026090808075462000_c24","doi-asserted-by":"publisher","first-page":"e2106018","DOI":"10.1002\/advs.202106018","article-title":"Highly efficient and stable blue organic light-emitting diodes based on thermally activated delayed fluorophor with donor-void-acceptor motif","volume":"9","year":"2022","journal-title":"Adv. Sci."},{"key":"2026090808075462000_c25","doi-asserted-by":"publisher","first-page":"1734","DOI":"10.1021\/acs.jpclett.4c00030","article-title":"Exploring the early time behavior of the excited states of an archetype thermally activated delayed fluorescence molecule","volume":"15","year":"2024","journal-title":"J.\u00a0Phys. Chem. Lett."},{"key":"2026090808075462000_c26","doi-asserted-by":"publisher","first-page":"14987","DOI":"10.1038\/ncomms14987","article-title":"Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters","volume":"8","year":"2017","journal-title":"Nat. Commun."},{"key":"2026090808075462000_c27","doi-asserted-by":"publisher","first-page":"8630","DOI":"10.1021\/acs.chemmater.7b02403","article-title":"Horizontally orientated sticklike emitters: Enhancement of intrinsic out-coupling factor and electroluminescence performance","volume":"29","year":"2017","journal-title":"Chem. Mater."},{"key":"2026090808075462000_c28","doi-asserted-by":"publisher","first-page":"19322","DOI":"10.1021\/acs.jpcc.9b03867","article-title":"Importance of conformational change in excited states for efficient thermally activated delayed fluorescence","volume":"123","year":"2019","journal-title":"J.\u00a0Phys. Chem. C"},{"key":"2026090808075462000_c29","doi-asserted-by":"publisher","first-page":"12400","DOI":"10.1021\/acs.jpcc.9b01900","article-title":"Intramolecular dimerization quenching of delayed emission in asymmetric D-D\u2032-A TADF emitters","volume":"123","year":"2019","journal-title":"J.\u00a0Phys. Chem. C"},{"key":"2026090808075462000_c30","doi-asserted-by":"publisher","first-page":"378","DOI":"10.1039\/d0cp05982j","article-title":"Understanding TADF: A joint experimental and theoretical study of DMAC-TRZ","volume":"23","year":"2021","journal-title":"Phys. Chem. Chem. Phys."},{"key":"2026090808075462000_c31","doi-asserted-by":"publisher","first-page":"313","DOI":"10.1039\/d1cp04905d","article-title":"Conformational disorder enabled emission phenomena in heavily doped TADF films","volume":"24","year":"2022","journal-title":"Phys. Chem. Chem. Phys."},{"key":"2026090808075462000_c32","doi-asserted-by":"publisher","first-page":"11057","DOI":"10.1021\/acs.jpcc.0c03369","article-title":"Defect-induced acceleration and deceleration of photocarrier recombination in SrTiO3 powders","volume":"124","year":"2020","journal-title":"J.\u00a0Phys. Chem. C"},{"key":"2026090808075462000_c33","doi-asserted-by":"publisher","first-page":"23897","DOI":"10.1021\/jp508233z","article-title":"Behavior and energy states of photogenerated charge carriers on Pt- or CoOx-loaded LaTiO2N photocatalysts: Time-resolved visible to mid-infrared absorption study","volume":"118","year":"2014","journal-title":"J.\u00a0Phys. Chem. C"},{"key":"2026090808075462000_c34","doi-asserted-by":"publisher","first-page":"12686","DOI":"10.1039\/d4sc00917g","article-title":"Boosting charge separation in organic photovoltaics: Unveiling dipole moment variations in excited non-fullerene acceptor layers","volume":"15","year":"2024","journal-title":"Chem. Sci."},{"key":"2026090808075462000_c35","doi-asserted-by":"publisher","first-page":"4534","DOI":"10.1021\/acs.jpca.0c11478","article-title":"Molecular vibration accelerates charge transfer emission in a highly twisted blue thermally activated delayed fluorescence material","volume":"125","year":"2021","journal-title":"J.\u00a0Phys. Chem. A"},{"key":"2026090808075462000_c36","doi-asserted-by":"publisher","first-page":"643","DOI":"10.1038\/s41566-020-0667-0","article-title":"Organic light emitters exhibiting very fast reverse intersystem crossing","volume":"14","year":"2020","journal-title":"Nat. Photonics"},{"key":"2026090808075462000_c37","doi-asserted-by":"publisher","first-page":"625","DOI":"10.1002\/cphc.202001013","article-title":"Efficient direct reverse intersystem crossing between charge transfer-type singlet and triplet states in a purely organic molecule","volume":"22","year":"2021","journal-title":"ChemPhysChem"},{"key":"2026090808075462000_c38","doi-asserted-by":"publisher","first-page":"562","DOI":"10.1021\/acs.jpclett.9b03302","article-title":"Observation of nonradiative deactivation behavior from singlet and triplet states of thermally activated delayed fluorescence emitters in solution","volume":"11","year":"2020","journal-title":"J.\u00a0Phys. Chem. Lett."}],"container-title":["The Journal of Chemical Physics"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/pubs.aip.org\/aip\/jcp\/article-pdf\/doi\/10.1063\/5.0350251\/21130330\/104703_1_5.0350251.pdf","content-type":"application\/pdf","content-version":"vor","intended-application":"syndication"},{"URL":"https:\/\/pubs.aip.org\/aip\/jcp\/article-pdf\/doi\/10.1063\/5.0350251\/21130330\/104703_1_5.0350251.pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,9,8]],"date-time":"2026-09-08T12:08:00Z","timestamp":1788869280000},"score":1,"resource":{"primary":{"URL":"https:\/\/pubs.aip.org\/jcp\/article\/165\/10\/104703\/3403924\/Substitution-dependent-excited-state-relaxation"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,9,8]]},"references-count":38,"journal-issue":{"issue":"10","published-print":{"date-parts":[[2026,9,14]]}},"URL":"https:\/\/doi.org\/10.1063\/5.0350251","relation":{},"ISSN":["0021-9606","1089-7690"],"issn-type":[{"value":"0021-9606","type":"print"},{"value":"1089-7690","type":"electronic"}],"subject":[],"published-other":{"date-parts":[[2026,9,14]]},"published":{"date-parts":[[2026,9,8]]},"article-number":"104703"}}