{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,10,7]],"date-time":"2026-10-07T02:58:43Z","timestamp":1791341923120,"version":"4.3.1"},"reference-count":56,"publisher":"AIP Publishing","issue":"21","content-domain":{"domain":["pubs.aip.org"],"crossmark-restriction":true},"short-container-title":[],"published-print":{"date-parts":[[2023,6,7]]},"abstract":"<jats:p>The diverse and tunable electronic structures of perylenediimide (PDI), together with its high thermal and chemical stability, make the compound suitable for applications in bioimaging, electrical, and optical devices. However, a large singlet\u2013triplet gap (\u0394ES\u2013T) and almost zero spin\u2013orbit coupling (SOC) between the lowest excited singlet (S1) and triplet (T1) restrict intersystem crossing (ISC) in highly fluorescent pristine PDI, yielding a near zero triplet quantum yield (\u03a6T). Interestingly, a thione analogs of PDI with varied S content (mS-PDIs, m = 1\u20134) was experimentally shown to yield \u03a6T \u223c 1.0 through efficient ISC. Time-dependent optimally-tuned range-separated hybrid calculations are performed to rationalize the experimentally observed red-shifted optical absorption and also the remarkably high ISC with almost zero radiative fluorescence reported for these mS-PDIs. To this end, the relative energies of low-lying excited singlets Sn (n = 1, 2) and a few triplets Tn(n = 1\u20133), along with their nature (n\u03c0* or \u03c0\u03c0*), are assessed for each of the mS-PDIs studied in chloroform. To our surprise and contrary to the earlier reports, both S1 and T1 are found to be of the same \u03c0\u03c0* character, originating from the highest occupied to lowest unoccupied orbital transition, which, therefore, leads to a still large \u0394ES\u2013T and vanishingly small SOC, as expected from the identical wavefunction symmetry. Increasing S content lowers S1(\u03c0\u03c0*) due to a greater extent of \u03c0-delocalization, which well complements and supports the observed red-shift. More importantly, the T2 (or T3) closely lying to the S1 is of n\u03c0* and, therefore, produces a relatively smaller \u0394ES\u2013T and larger SOC. Detailed kinetics analysis suggests S1(\u03c0\u03c0*) \u2192 T2(n\u03c0*) is the primary ISC channel for all mS-PDIs, which is responsible for the remarkably high \u03a6T observed. In addition, comparable SOC and \u0394ES\u2013T produce similar ISC rates for all mS-PDIs.<\/jats:p>","DOI":"10.1063\/5.0152082","type":"journal-article","created":{"date-parts":[[2023,6,2]],"date-time":"2023-06-02T07:22:09Z","timestamp":1685690529000},"update-policy":"https:\/\/doi.org\/10.1063\/aip-crossmark-policy-page","source":"Crossref","is-referenced-by-count":18,"title":["Understanding remarkably high triplet quantum yield in thione analogs of perylenediimide: A detailed theoretical study"],"prefix":"10.1063","volume":"158","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-4497-8807","authenticated-orcid":false,"given":"Raka","family":"Ahmed","sequence":"first","affiliation":[{"name":"Department of Chemistry, Indian Institute of Technology Tirupati , Tirupati, A.P 517619, India"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8893-2288","authenticated-orcid":false,"given":"Arun K.","family":"Manna","sequence":"additional","affiliation":[{"name":"Department of Chemistry, Indian Institute of Technology Tirupati , Tirupati, A.P 517619, India"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"317","published-online":{"date-parts":[[2023,6,2]]},"reference":[{"key":"2023081121201198100_c1","doi-asserted-by":"publisher","first-page":"5323","DOI":"10.1039\/c3cs35531d","article-title":"Triplet photosensitizers: From molecular design to applications","volume":"42","year":"2013","journal-title":"Chem. 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