{
  "abstract": "The quintet-to-singlet back-switching process in [Fe(tpy)2]2+(tpy=2,2’:6’,2\"-terpyridine), [Fe(dftpy)2]2+ (dftpy=6,6\"-difluoro-2,2’:6’,2\"-terpyridine) and [Fe(dctpy)2]2+(dctpy=6,6\"-dichloro-2,2’:6’,2\"-terpyridine), together with the photorelaxation dynamics of the [Fe(dftpy)2]2+ spin-crossover and the [Fe(dctpy)2]2+ high-spin complexes were investigated by full-dimensional trajectory surface hopping (TSH) dynamics. Following photoexcitation, the initial population of the 5Eg (5MC) state decays quickly via a branching mechanism of direct (5Eg → 5T2g) and 3MC-crossed (5Eg → 3MC→5T2g) processes, with the latter dominating the dynamics. The quintet-to-singlet photoconversion, the key step of the back-switching process, remains inefficient (<10%). This low efficiency arises because the singlet–triplet–quintet crossing region is readily accessible only during the initial sub-picosecond dynamics (<500 fs). Shifting the crossing region to improve its accessibility could substantially enhance the quintet-to-singlet conversion efficiency, suggesting that more extensive chemical modification could significantly optimize the back-switching process. Upon excitation to the quintet MLCT manifold, the population decays within <200 fs to the dark 5Eg (5MC) state (followed by the relaxation to the 5T2g (5MC) in less than 1 ps); only 1-2% of the initial population remains in the ligand-centered states in all complexes. In contrast, previous transient absorption spectroscopy experiments identified a long-lived 5/7MLCT state for [Fe(dftpy)2]2+ and [Fe(dctpy)2]2+, potentially because the analysis was restricted to picosecond timescales and probe wavelengths were used at which 5MC states are dark.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": null,
  "author_total": 4,
  "authors": [
    {
      "name": "Dániel Buzsáki"
    },
    {
      "name": "György Vankó"
    },
    {
      "name": "Tamás Rozgonyi"
    },
    {
      "name": "Mátyás Pápai"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/dtn6y0087z8e8.bib",
  "cited_by": 0,
  "doi": "10.26434/chemrxiv.15006375/v2",
  "fulltext_url": null,
  "id": "dtn6y0087z8e8",
  "issns": [],
  "landing_url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15006375/v2",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "journal",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "2504|Magnetism in coordination complexes"
    ]
  ],
  "openalex": "W7212025383",
  "pdf_url": "https://chemrxiv.org/doi/pdf/10.26434/chemrxiv.15006375/v2",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-09",
  "publisher": "American Chemical Society (ACS)",
  "ris": "https://research.draconitic.com/paper/dtn6y0087z8e8.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:17:19Z",
      "native_id": "10.26434/chemrxiv.15006375",
      "source": "chemrxiv",
      "url": "https://chemrxiv.org/doi/full/10.26434/chemrxiv.15006375/v2"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:2504|Magnetism in coordination complexes",
      "subfield": "materials-polymers"
    }
  ],
  "title": "Simulation of Ultrafast Fe(II) Photoswitching Dynamics Triggered by Excitation within the Quintet Manifold",
  "title_text": "Simulation of Ultrafast Fe(II) Photoswitching Dynamics Triggered by Excitation within the Quintet Manifold",
  "type": "preprint",
  "updated_at": "2026-10-30T12:17:19Z",
  "url": "https://research.draconitic.com/paper/dtn6y0087z8e8",
  "venue": "ChemRxiv",
  "versions": []
}