{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,12,5]],"date-time":"2025-12-05T13:27:08Z","timestamp":1764941228590,"version":"3.46.0"},"reference-count":40,"publisher":"MDPI AG","issue":"24","license":[{"start":{"date-parts":[[2025,12,5]],"date-time":"2025-12-05T00:00:00Z","timestamp":1764892800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"MIUR Progetti di Ricerca di Rilevante Interesse Nazionale (PRIN) Bando","award":["P2022FY5NK_003"],"award-info":[{"award-number":["P2022FY5NK_003"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>The osmium(II) polypyridyl complex [Os(tpy)(pydppn)]2+ (tpy = 2,2\u2032:6\u2032,2\u2033-terpyridine; pydppn = 3-(pyrid-2\u2032-yl)-4,5,9,16-tetraaza-dibenzo[a,c]naphthacene) was synthesized and characterized to evaluate the effect of an extended planar \u03c0-system on photophysical properties and DNA interactions. This complex represents the \u03c0-expanded analog of the previously studied [Os(tpy)(pydppz)]2+ system. Electrochemical studies revealed a reversible Os(II)\/Os(III) oxidation at +0.99 V vs. SCE and five ligand-centered reductions, generally less negative than those of the smaller pydppz analog, consistent with enhanced electron-accepting ability. In acetonitrile, the complex exhibits UV absorption bands at 328 and 473 nm and near-infrared emission at 840 nm, assigned to a long-lived 3MLCT state (\u03c4 = 110 ns, \u03a6 = 0.02). Upon titration with calf-thymus DNA, [Os(tpy)(pydppn)]2+ shows a pronounced light-switch effect, hypochromism, red-shifted MLCT bands, induced circular dichroism, and an increase in DNA melting temperature (\u0394Tm = 8.9 \u00b1 0.5 \u00b0C), consistent with intercalative binding. Viscometric titrations further support intercalation, with a binding constant KB \u2248 1.2 \u00d7 106 M\u22121. Transient absorption spectroscopy indicates that DNA binding prolongs the excited-state lifetime and modifies vibrational relaxation pathways. These results highlight how \u03c0-system extension in Os(II) complexes modulates photophysical behavior and DNA affinity, offering insights for the rational design of NIR-emitting, DNA-targeted luminescent probes and potential phototherapeutic agents.<\/jats:p>","DOI":"10.3390\/molecules30244671","type":"journal-article","created":{"date-parts":[[2025,12,5]],"date-time":"2025-12-05T13:17:07Z","timestamp":1764940627000},"page":"4671","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Lighting Up DNA in the Near-Infrared: An Os(II)\u2013pydppn Complex with Light-Switch Behavior"],"prefix":"10.3390","volume":"30","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-3234-7650","authenticated-orcid":false,"given":"Emanuela","family":"Trovato","sequence":"first","affiliation":[{"name":"Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Universit\u00e0 degli Studi di Messina and Centro Interuniversitario per la Conversione dell\u2019Energia Solare (SOLARCHEM), Via F. Stagno d\u2019Alcontres 31, 98166 Messina, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3393-6457","authenticated-orcid":false,"given":"Salvatore","family":"Genovese","sequence":"additional","affiliation":[{"name":"Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Universit\u00e0 degli Studi di Messina and Centro Interuniversitario per la Conversione dell\u2019Energia Solare (SOLARCHEM), Via F. Stagno d\u2019Alcontres 31, 98166 Messina, Italy"},{"name":"Dipartimento di Chimica, Biologia e Biotecnologie, University of Perugia, 8, Via dell\u2019Elce di sotto, 06123 Perugia, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5892-907X","authenticated-orcid":false,"given":"Maurilio","family":"Galletta","sequence":"additional","affiliation":[{"name":"CNR-Istituto per la Microelettronica e Microsistemi (IMM), Viale F. Stagno d\u2019Alcontres 31, 98166 Messina, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3385-2528","authenticated-orcid":false,"given":"Sebastiano","family":"Campagna","sequence":"additional","affiliation":[{"name":"Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Universit\u00e0 degli Studi di Messina and Centro Interuniversitario per la Conversione dell\u2019Energia Solare (SOLARCHEM), Via F. Stagno d\u2019Alcontres 31, 98166 Messina, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2015-3747","authenticated-orcid":false,"given":"Maria Letizia","family":"Di Pietro","sequence":"additional","affiliation":[{"name":"Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Universit\u00e0 degli Studi di Messina and Centro Interuniversitario per la Conversione dell\u2019Energia Solare (SOLARCHEM), Via F. Stagno d\u2019Alcontres 31, 98166 Messina, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8579-859X","authenticated-orcid":false,"given":"Fausto","family":"Puntoriero","sequence":"additional","affiliation":[{"name":"Dipartimento di Scienze Chimiche, Biologiche, Farmaceutiche ed Ambientali, Universit\u00e0 degli Studi di Messina and Centro Interuniversitario per la Conversione dell\u2019Energia Solare (SOLARCHEM), Via F. Stagno d\u2019Alcontres 31, 98166 Messina, Italy"},{"name":"CNR-Istituto per la Microelettronica e Microsistemi (IMM), Viale F. Stagno d\u2019Alcontres 31, 98166 Messina, Italy"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2025,12,5]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"4960","DOI":"10.1021\/ja00168a052","article-title":"A molecular light switch for DNA: Ru(bpy)2(dppz)2+","volume":"112","author":"Friedman","year":"1990","journal-title":"J. Am. Chem. Soc."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"6427","DOI":"10.1021\/ic800560x","article-title":"Role of electronic structure on DNA light switch behavior of Ru(II) intercalators","volume":"47","author":"Sun","year":"2008","journal-title":"Inorg. Chem."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Di Pietro, M.L., La Ganga, G., Puntoriero, F., and Nastasi, F. (2021). Ru(II)-Dppz derivatives and their interactions with DNA: Thirty years and counting. Appl. 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