{
  "abstract": "Detailed photophysical measurements of the non-symmetric heptazine, HzTFEX ₂ , previously reported as having inverted S ₁ -T ₁ levels, show complex behaviour, highly dependent on environment, concentration and aggregation. Here we show that, single crystals of HzTFEX ₂ show anti-Kasha S ₀ ←S ₂ and excimer emission. Solution state absorption shows a hypsochromic shift of the π-π* S ₀ →S ₁ , linearly dependent on solvent polarizability. In most environments, emission is dominated by excimer species, only in toluene and frozen 2-MeTHF do monomeric properties dominate. In frozen solutions, aggregation phenomena are solvent dependent. Given such complexity, time-dependent emission spectra are crowded, making it difficult to resolve monomeric phosphorescence. However, by exciting S ₀ →S ₂ at 77 K, we observe a consistent phosphorescence signal at 425 nm, 110 ± 20 meV above the S ₀ ←S ₁ emission, whereas exciting S ₀ →S ₁ does not give phosphorescence or delayed fluorescence (DF). We conclude that coupling between S ₂ and S ₁ is very weak, S ₂ -T N intersystem crossing is effective, whereas S ₁ ↔T ₁ intersystem crossing is thermally activated, fulfilling the conditions required for the observation of inverted phosphorescence. At room temperature, no long-lived DF is observed because exothermic T ₁ →S ₁ ISC becomes allowed, such that in an OLED, high efficiency can be achieved.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": null,
  "author_total": 5,
  "authors": [
    {
      "name": "Carolina Francener",
      "orcid": "0000-0002-3886-167X"
    },
    {
      "name": "Hector Miranda-Salinas",
      "orcid": "0000-0001-6403-5251"
    },
    {
      "name": "Christopher J. Riggs",
      "orcid": "0000-0002-9282-2321"
    },
    {
      "name": "Naoya Aizawa",
      "orcid": "0000-0003-4673-4512"
    },
    {
      "name": "Andrew Monkman",
      "orcid": "0000-0002-0784-8640"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/5fmy6tt99048e.bib",
  "cited_by": 0,
  "doi": "10.1038/s41467-026-78831-z",
  "fulltext_url": null,
  "id": "5fmy6tt99048e",
  "issns": [
    "2041-1723"
  ],
  "landing_url": "https://www.nature.com/articles/s41467-026-78831-z",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2505|Luminescence and Fluorescent Materials"
    ]
  ],
  "openalex": "W7223001464",
  "pdf_url": "https://www.nature.com/articles/s41467-026-78831-z_reference.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-20",
  "publisher": "Springer Science and Business Media LLC",
  "ris": "https://research.draconitic.com/paper/5fmy6tt99048e.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:39Z",
      "native_id": "10.1038/s41467-026-78831-z",
      "source": "crossref",
      "url": "https://www.nature.com/articles/s41467-026-78831-z"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:2505|Luminescence and Fluorescent Materials",
      "subfield": "materials-polymers"
    }
  ],
  "title": "Comprehensive spectroscopic analysis of energy inversion of the lowest singlet and triplet excited states in the heptazine HzTFEX2",
  "title_text": "Comprehensive spectroscopic analysis of energy inversion of the lowest singlet and triplet excited states in the heptazine HzTFEX2",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:17:39Z",
  "url": "https://research.draconitic.com/paper/5fmy6tt99048e",
  "venue": "Nature Communications",
  "versions": []
}