Efficient Emission of Ultraviolet Light by Solid State Organic Fluorophores: Synthesis and Characterization of 1,4‐Dialkeny‐2,5‐dioxybenzenes

• Published in: Chemistry : a European journal 2021-01, Vol.27 (5), p.1626-1637
• Main Authors: Shimizu, Masaki, Nishimura, Kenta, Hirakawa, Rika, Sakurai, Tsuneaki
• Format: Article
• Language: English
• Subjects: Benzene; Charge transfer; Chemical compounds; Chemistry; Density functional theory; donor–acceptor systems; Emission; Fluorescence; Fluorophores; materials science; Oxygen; Oxygen atoms; photochemistry; Polymethyl methacrylate; Solid state; Substitutes; Thin films; Ultraviolet radiation
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202003526

The design and development of organic luminophores that exhibit efficient ultraviolet (UV) fluorescence in the solid state remains underexplored. Here, we report that 1,4‐dialkenyl‐2,5‐dialkoxybenzenes and 1,4‐dialkenyl‐2,5‐disiloxybenzenes act as such UV‐emissive fluorophores. The dialkenyldioxybenzenes were readily prepared in three steps from 2,5‐dimethoxy‐1,4‐diacetylbenzene or 2,5‐dimethoxy‐1,4‐diformylbenzene via two to four steps from 1,4‐bis(diethoxyphosphonylmethyl)‐2,5‐dimethoxybenzene. The dialkenyldioxybenzenes emit UV light in solution (λem=350–387 nm) and in the solid state (λem=328–388 nm). In addition, the quantum yields in the solid state were generally higher than those in solution. In particular, the adamantylidene‐substituted benzenes fluoresced in the UV region with high quantum yields (Φ=0.37–0.55) in the solid state. Thin films of poly(methyl methacrylate) doped with the adamantylidene‐substituted benzenes also exhibited UV emission with good efficiency (Φ=0.27–0.45). Density functional theory calculations revealed that the optical excitation of the dialkenyldimethoxybenzenes involves intramolecular charge‐transfer from the ether oxygen atoms to the twisted alkenyl‐benzene‐alkenyl moiety, whereas the dialkenylbis(triphenylsiloxy)benzenes were optically excited through intramolecular charge‐transfer from the oxygen atoms and twisted π‐system to the phenyl‐Si moieties of each triphenylsilyl group. Beyond visible‐light region: 1,4‐Dialkenyl‐2,5‐dioxybenzenes were developed as organic fluorophores whose emission maxima appears in the ultraviolet region with good‐to‐high solid‐state quantum yields. The synthesis of the UV‐emissive benzenes is easy, and the use of an adamantylidene moieties as the alkenyl parts results in efficient solid‐state UV fluorescence. Density functional theory calculations reveal that the electronic structures of the UV‐emissive benzenes differ depending on whether the substituents on the phenolic oxygen atoms are carbonaceous or aryl silyl groups.