Reproducible switching of the polymorph‐dependent excited‐state intramolecular proton‐transfer (ESIPT) luminescence of an imidazo[1,2‐a]pyridine between blue‐green and yellow (see picture) is achieved by thermal control of its solid‐state molecular packing. Thus, ESIPT is a promising mechanism for packing‐to‐luminescence transduction and amplification that offers a novel design concept for tunable organic luminescent solids.
In the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene or 1,5-diazabicyclo[4.3.0]non-5-ene, metal-free phthalocyanine was obtained by heating phthalonitrile in alcohols. Addition of a copper(II) salt in the reaction gave copper phthalocyanine in a good yield.
Organic, white luminescent materials were fabricated using a mixture of proton-transfer and nonproton-transfer fluorophores. 2'-Methoxy and 2'-hydroxy derivatives of 2-phenylimidazo[1,2-a]pyridine (PIP) have similar UV-absorption properties; however, they exhibit mechanistically different luminescence respectively ascribable to the normal (∼420 nm) and excited-state intramolecular proton transfer processes (∼530 nm) in the solid state. UV-irradiation of mixed solids excites both components concurrently and results in efficient white luminescence composed of two independent emissions without involving energy transfer process. White luminescent solids are easily transformed into vapor-deposited films under mild conditions, and a colorless and transparent thin film by dissolving in PMMA.
Several metallophthalocyanines (MPc: M=Ni(II), Co(II), Zn(II), Pb(II), Fe(II), Sn(II), Cd(II), Mg(II), and Mn(III)) were obtained by heating phthalonitrile with metal salts in alcohols in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene. Metal acetylacetonates as well as metal halides were available as metal sources for preparation of metallophthalocyanines by this method.
In order to search for novel fluorescent organic compounds, 20 derivatives of imidazo[1,2-a]pyridine (1) were synthesized, and their fluorescent properties were studied. Though the parent compound 1 (λfl = 370.5 nm, Φ = 0.57 in ethanol) was in the liquid state at ambient temperature, 2-phenylimidazo[1,2-a]pyridine (5), 2-(2-naphthyl)imidazo[1,2-a]pyridine (16), 7-methylimidazo[1,2-a]pyridine (3), 7-methyl-2-phenylimidazo[1,2-a]pyridine (12), and 7-methyl-2-(2-naphthyl)imidazo[1,2-a]pyridine (17) were found to give thermally stable solid compounds (mp 55—190 °C) without much affecting the fluorescent properties of the parent compound (λfl = 374—381 nm, Φ = 0.50—0.78 in ethanol). Among the 4′-substituted 2-phenyl derivatives, it was found that the introduction of the strong electron-donating amino and dimethylamino groups (2-(4-aminophenyl)imidazo[1,2-a]pyridine (7) and 2-[4-(dimethylamino)phenyl]imidazo[1,2-a]pyridine (8), respectively) caused marked red shift of their fluorescence (λfl = 445 and 446 nm, respectively, in ethanol), thus providing the way for tuning the fluorescence color of the IP derivatives. The observed red shift of the fluorescence of 7 and 8 was ascribed to the contribution of the excited intramolecular charge transfer state.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.