title: Visible room-temperature phosphorescence of pure organic crystals via a radical-ion-pair mechanism.
abstract: The afterglow of phosphorescent compounds can be distinguished from background fluorescence and scattered light by a time-resolved observation, which is a beneficial property for bioimaging. Phosphorescence emission accompanies spin-forbidden transitions from an excited singlet state through an excited triplet state to a ground singlet state. Since these intersystem crossings are facilitated usually by the heavy-atom effect, metal-free organic solids are seldom phosphorescent, although these solids have recently been refurbished as low-cost, eco-friendly phosphorescent materials. Here, we show that crystalline isophthalic acid exhibits room-temperature phosphorescence with an afterglow that lasts several seconds through a nuclear spin magnetism-assisted spin exchange of a radical ion pair. The obvious afterglow that facilitates a time-resolved detection and the unusual phosphorescence mechanism that enables emission intensification by nuclear spin managements are promising for exploiting the phosphorescence materials in novel applications such as bioimaging.
authors.affiliation: Department of Life Science, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, 4259 J2-10, Nagatsutacho, Midoriku, Yokohama 226-8501, Japan. hyuasa@bio.titech.ac.jp.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kuno
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Akeno
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ohtani
authors.forename: Hideya
authors.initials: H
authors.lastname: Yuasa
mesh_terms: D003460:Crystallization; D005609:Free Radicals / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D049449:Luminescence; D010795:Phthalic Acids / Q000737:chemistry*; D011789:Quantum Theory; D013696:Temperature
chemical_list: D005609:Free Radicals; D007477:Ions; D010795:Phthalic Acids; C059768:isophthalate