{
  "abstract": "Photolabile protecting groups (PPGs) are indispensable tools for spatiotemporally controlled release of reactive functional groups. Recently, we proposed a quantum spin-manipulation (QSM-1) strategy that employs triplet ground-state cations to render ion-pair recombination spin-forbidden, thereby enhancing the uncaging quantum yield. In this study, the photodissociation mechanism of a 2-(4-nitrophenyl)-1H-indole-3-ylmethyl (NPIM) photocage bearing a benzoate leaving group was investigated to evaluate the effectiveness of a triplet excited-state-mediated QSM pathway (QSM-2). Spectroscopic analyses revealed that the excited state of NPIM possesses a relatively small singlet-triplet energy gap (ΔEST = 5.3 kcal mol-1), enabling efficient intersystem crossing (ISC) from the intramolecular charge-transfer singlet excited state to the triplet excited state. Oxygen-quenching experiments demonstrated that photodissociation proceeds predominantly from the triplet excited state. Time-resolved absorption spectroscopy identified the singlet excited state (τ = 1.6 ns), triplet excited state (τ = 2.3 μs), and NPIM radical intermediate (τ = 1.5 ms). In situ infrared analysis directly detected benzoic acid, an oxidized NPIM product, and CO2 generated from the benzoyl radical, supporting a homolytic bond-cleavage mechanism. Ultrafast time-resolved infrared spectroscopy of the NPIM chromophore revealed formation of a twisted intramolecular charge-transfer state that promotes ISC by reducing ΔEST. Density functional theory calculations further indicate that C-O bond homolysis from the triplet excited state is energetically feasible and is driven by relief of excited-state antiaromaticity. These results establish that uncaging of NPIM derivatives proceeds through triplet-state homolysis and demonstrate the validity of the QSM-2 strategy for designing efficient photochemical release systems.",
  "abstract_shown": true,
  "affiliations": [
    "The Institute for Solid State Physics, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba277-8581, Japan.",
    "Department of Chemistry, Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-Hiroshima, Hiroshima739-8526, Japan.",
    "Hiroshima Research Center for Photo-Drug-Delivery Systems (Hi-P-DDS), Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima739-8526, Japan."
  ],
  "article_type": "research article",
  "arxiv": null,
  "author_total": 9,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "Kenta Kuroishi"
    },
    {
      "affs": [
        1
      ],
      "name": "Ryuei Hayashi"
    },
    {
      "affs": [
        1
      ],
      "name": "Ryoko Oyama"
    },
    {
      "affs": [
        0
      ],
      "name": "Shunsuke Tanaka"
    },
    {
      "affs": [
        0
      ],
      "name": "Kotaro Ogawa"
    },
    {
      "affs": [
        0
      ],
      "name": "Yuta Murotani",
      "orcid": "0000-0003-3071-6408"
    },
    {
      "affs": [
        0
      ],
      "name": "Ryusuke Matsunaga",
      "orcid": "0000-0001-9674-5100"
    },
    {
      "affs": [
        0
      ],
      "name": "Jun Yoshinobu",
      "orcid": "0000-0001-7774-8701"
    },
    {
      "affs": [
        1,
        2
      ],
      "name": "Manabu Abe",
      "orcid": "0000-0002-2013-4394"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/2wmaf8bptr9fa.bib",
  "cited_by": 0,
  "doi": "10.1021/jacs.6c13942",
  "fulltext_url": "https://europepmc.org/articles/PMC13587664",
  "id": "2wmaf8bptr9fa",
  "issns": [
    "0002-7863",
    "1520-5126"
  ],
  "landing_url": "https://europepmc.org/article/MED/42915514",
  "language": "eng",
  "licence": "CC-BY-NC-ND",
  "licence_label": "CC BY-NC-ND",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by-nc-nd/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "openalex",
      "1606|Photochemistry and Electron Transfer Studies"
    ]
  ],
  "openalex": "W7207521349",
  "pdf_url": "https://europepmc.org/articles/PMC13587664?pdf=render",
  "pmcid": "PMC13587664",
  "pmid": "42915514",
  "published": "2026-09-01",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/2wmaf8bptr9fa.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:21:02Z",
      "native_id": "MED:42915514",
      "source": "europepmc",
      "url": "https://europepmc.org/article/MED/42915514"
    }
  ],
  "subjects": [
    {
      "field": "chemistry",
      "origin": "openalex:1606|Photochemistry and Electron Transfer Studies",
      "subfield": "physical"
    }
  ],
  "title": "Mechanistic Insights into Photo-Induced Bond Dissociation of a 2-(4-Nitrophenyl)-1H-indole-3-ylmethyl (NPIM) Derivative: A Case Study on Quantum Spin-Manipulation for Uncaging.",
  "title_text": "Mechanistic Insights into Photo-Induced Bond Dissociation of a 2-(4-Nitrophenyl)-1H-indole-3-ylmethyl (NPIM) Derivative: A Case Study on Quantum Spin-Manipulation for Uncaging.",
  "type": "peer-reviewed",
  "updated_at": "2026-10-30T12:21:02Z",
  "url": "https://research.draconitic.com/paper/2wmaf8bptr9fa",
  "venue": "Journal of the American Chemical Society",
  "versions": []
}