{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,9]],"date-time":"2026-10-09T11:55:33Z","timestamp":1791546933321,"version":"4.3.4"},"reference-count":45,"publisher":"AIP Publishing","issue":"14","content-domain":{"domain":["pubs.aip.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2026,10,14]]},"abstract":"<jats:p>Multi-resonance thermally activated delayed fluorescence emitters typically rely on rigid, symmetry-defined molecular frameworks to achieve narrowband emission and small singlet\u2013triplet energy gaps (\u0394EST), but such symmetry often suppresses static spin\u2013orbit coupling (SOC), making reverse intersystem crossing (RISC) dependent on vibronic assistance. Here, the recently reported emitter 2S-BN was adopted as a model system to examine how molecular-symmetry reduction, accompanied by non-planar structural distortion, affects spin-conversion pathways. Two symmetry-reduced derivatives, A and B, were computationally designed through peripheral substituent removal and asymmetric framework modification. Density functional theory, SOC calculations, and thermal vibration correlation function simulations reveal that the C2v-symmetric parent 2S-BN exhibits nearly vanishing Franck\u2013Condon SOC, whereas the symmetry-reducing structural modifications make finite static FC-SOC contributions accessible in A and B, with values of \u223c0.20 and 0.18\u00a0cm\u22121, respectively. The absorption and emission energies remain comparable across the series, suggesting preservation of the essential multi-resonance character. Under the same computational protocol, the calculated kRISC values of A and B are only \u223c3.3 and 2.2 times larger than those of 2S-BN. This modest increase is not caused by a larger total effective SOC; the effective SOC of 2S-BN exceeds those of A and B. In the present rate model, the kISC values remain nearly unchanged, because a large FCWD-related factor offsets the smaller |SOCeff|2 of A and B. The faster kRISC then follows mainly from their smaller \u0394ESTadi through the Boltzmann relation. Within this molecular series, symmetry reduction, inseparably accompanied by non-planar distortion, therefore provides a handle on the accessibility of static vs vibronic SOC contributions rather than a standalone control of the RISC rate.<\/jats:p>","DOI":"10.1063\/5.0350590","type":"journal-article","created":{"date-parts":[[2026,10,9]],"date-time":"2026-10-09T11:43:13Z","timestamp":1791546193000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":0,"title":["Static vs Herzberg\u2013Teller spin\u2013orbit coupling under symmetry-reducing distortion in multi-resonance TADF emitters"],"prefix":"10.1063","volume":"165","author":[{"ORCID":"https:\/\/orcid.org\/0009-0000-1920-4837","authenticated-orcid":false,"given":"Lu","family":"Wang","sequence":"first","affiliation":[{"name":"College of Chemistry, Jilin University 1 , Changchun 130012,","place":["China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0009-0005-2154-0238","authenticated-orcid":false,"given":"Xiao-Li","family":"Wang","sequence":"additional","affiliation":[{"name":"College of Chemistry, Jilin University 1 , Changchun 130012,","place":["China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xue-Ju","family":"Lv","sequence":"additional","affiliation":[{"name":"College of Chemistry, Jilin University 1 , Changchun 130012,","place":["China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Li-Chun","family":"Liu","sequence":"additional","affiliation":[{"name":"Changchun Technical University of Automobile 2 , Changchun 130013,","place":["China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-4670-7741","authenticated-orcid":false,"given":"Jian","family":"Wang","sequence":"additional","affiliation":[{"name":"College of Chemistry, Jilin University 1 , Changchun 130012,","place":["China"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"317","published-online":{"date-parts":[[2026,10,9]]},"reference":[{"key":"2026100907430795400_c1","doi-asserted-by":"publisher","first-page":"083302","DOI":"10.1063\/1.3558906","article-title":"Efficient up-conversion of triplet excitons into a singlet state and its application for organic light emitting diodes","volume":"98","year":"2011","journal-title":"Appl. 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