[Show abstract][Hide abstract] ABSTRACT: Phospha-fluorescein (POF), a phosphine oxide-containing analogue of fluorescein, was synthesized and its photophysical properties were examined. Compared with fluorescein and sila-fluorescein, POF displayed significantly red-shifted absorption and fluorescence as well as superior photobleaching resistance, while retaining the pH-responsive characteristics of fluorescein dyes.
No preview · Article · Jan 2016 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: Ladder π-conjugated materials and also push-pull systems belong to important classes of compounds for the development of organic electronic devices. In this communication, a novel π-conjugated material that unifies the properties of both of these classes is presented. The material comprises a rigid biphenyl framework, which bears two bridging electron-accepting phosphine oxide moieties as well as two electron-donating amino groups. The structure and photophysical properties of this compound are discussed and compared with those of a related system lacking the second P-moiety.
No preview · Article · Jan 2016 · Chemical Communications
[Show abstract][Hide abstract] ABSTRACT: Fluorophores with intramolecular charge-transfer (ICT) character in the excited state exhibit significant solvatochromism of their fluorescence. Here, we report an example for such compounds, a benzophosphole P-oxide bearing an electron-donating p-(diphenylamino)phenyl group at the 3-position. While this compound shows only subtle dependence of the absorption maximum on the solvent polarity (lambda(max) = 383-392 nm), its emission maximum is significantly red-shifted upon increasing the solvent polarity (cyclohexane: lambda(em) = 457 nm; DNIF: lambda(em) = 598 nm). Most notably, the fluorescence quantum yields gradually increase with increased Stokes shifts, ultimately reaching Phi(F) = 0.28 in DMF. This trend is fundamentally different from that observed for the corresponding 2-(diphenylamino)phenyl-substituted benzophosphole congener, for which applications as a fluorescent bioimaging probe were previously demonstrated. In this study, the origins of this striking difference are examined by a combined experimental and theoretical approach. Our results suggest that the observed difference arises from a significant contribution of quinoidal resonance forms in the ICT excited state, which suppresses nonradiative decay and hence increases the quantum yield in polar solvents.
No preview · Article · Nov 2015 · Bulletin of the Chemical Society of Japan
[Show abstract][Hide abstract] ABSTRACT: Electron-donating aryl groups were attached to electron-accepting benzophosphole skeletons. Among several derivatives thus prepared, one benzophosphole oxide was particularly interesting, as it retained high fluorescence quantum yields even in polar and protic solvents. This phosphole-based compound exhibited a drastic color change of its fluorescence spectrum as a function of the solvent polarity, while the absorption spectra remained virtually unchanged. Capitalizing on these features, this phosphole-based compound was used to stain adipocytes, in which the polarity of subcellular compartments could then be discriminated on the basis of the color change of the fluorescence emission.
No preview · Article · Mar 2015 · Angewandte Chemie
[Show abstract][Hide abstract] ABSTRACT: Pyridine N-oxide-BF2 CF3 and -BF2 C2 F5 complexes and their derivatives were synthesized. Most of the complexes show fluorescence both in solution and in the solid state. By expanding the π-conjugated skeleton, the color of the fluorescence could be changed dramatically. A fluorophore with a high solvent dependency could also be produced. Since such compounds can be synthesized on a gram scale in high yield, and are stable to oxygen, water, and heat, the complexes hold great potential as organic functional materials.
No preview · Article · Apr 2014 · Chemistry - An Asian Journal
[Show abstract][Hide abstract] ABSTRACT: The efficient fourfold radical phosphanylation of 2,2,2′,2′- tetrabromobiphenyl with a bis(stannyl)phosphane followed by oxidation produces a highly strained biphenyl with two phosphoryl bridges (see picture). Extended π-conjugated compounds consisting of this core unit can be also synthesized by using the same approach. The two phosphoryl bridges significantly alter the electronic structure, making this biphenyl a unique electron-accepting scaffold.
No preview · Article · Dec 2011 · Angewandte Chemie International Edition
[Show abstract][Hide abstract] ABSTRACT: Die effiziente vierfache radikalische Phosphanylierung von 2,2,2′,2′-Tetrabrombiphenyl mit einem Bis(stannyl)phosphan, gefolgt von P-Oxidation, führt zu gespannten Biphenylen mit zwei Phosphorylbrücken (siehe Bild). Verlängerte π-konjugierte Verbindungen mit diesem Biphenylkern können auch durch die mehrfache radikalische Phosphanylierung synthetisiert werden. Die zwei Phosphorylbrücken machen das Biphenyl zu einem einzigartigen elektronenziehenden Gerüst.
No preview · Article · Dec 2011 · Angewandte Chemie
[Show abstract][Hide abstract] ABSTRACT: The synthesis and properties of the phosphonium- and borate-bridged stilbenes are reported. The zwitterionic ladder stilbenes were synthesized by the intramolecular cascade cyclization from the phosphanyl- and boryl-substituted diphenylacetylenes 1. The study of the substituent effects of the phosphanyl and boryl groups revealed the significant dependence of the reactivity on both the nucleophilicity of the phosphanyl group and the electrophilicity of the boryl group. Theoretical calculations indicated that this reaction is initiated by the nucleophilic attack of the phosphanyl group, irrespective of the degree of the electrophilicity of the boryl group, in contrast to the analogous intermolecular reaction promoted by the frustrated Lewis pairs of R3P and B(C6F5)3. Moreover, even in the case of compound 1c, which does not undergo cascade cyclization under thermal conditions, photoexcitation promoted the cyclization to produce the corresponding zwitterionic stilbene 2c, indicative of the potential use as a photoresponsive material. The photophysical properties of a series of zwitterionic stilbenes, 2a–e, also display dependence on the substituents. The fluorescence quantum yields (ΦF) of the stilbenes 2d and 2e, with electron-withdrawing diarylboryl groups, were an order of magnitude higher than those of 2a–c, with a dimesitylboryl group. Time-resolved fluorescence spectroscopy as well as the measurement of ΦF in the polymer matrices revealed that the electron-withdrawing diarylboryl groups significantly retarded the nonradiative decay process from the singlet excited state, resulting in a higher ΦF.