Fluorescent Dyes and Their Supramolecular Host/Guest Complexes with Macrocycles in Aqueous Solution Roy N. Dsouza, Uwe Pischel,* and Werner M. Nau* School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, D-28759 Bremen, Germany Centro de Investigaci on en Química Sostenible (CIQSO) and Departamento de Ingeniería Química, Química Física y Química Org anica, Universidad de Huelva, Campus de El Carmen s/n, E-21071 Huelva, Spain

Fluorescent dyes and their supramolecular host/guest complexes with macrocycles in aqueous solution.

ConspectusHydrogen has been labeled the fuel of the future since it contains no carbon, has the highest specific enthalpy of combustion of any chemical fuel, yields only water upon complete oxidation, and is not limited by Carnot considerations in the amount of work obtained when used in a fuel cell. To be used on the scale needed for sustainable growth on a global scale, hydrogen must be produced by the light-driven splitting of water into its elements, as opposed to reforming of methane, as is currently done. The photochemical generation of H2, which is the reductive side of the water splitting reaction, is the focus of this Account, particularly with regard to work done in the senior author’s laboratory over the last 5 years. Despite seminal work done more than 30 years ago and the extensive research conducted since then on all aspects of the process, no viable system has been developed for the efficient and robust photogeneration of H2 from water using only earth abundant elements. For the photogenera...

Fuel from Water: The Photochemical Generation of Hydrogen from Water

A highly efficient visible-light-induced hydrogen evolution system without an electron mediator such as methyl viologen, constructed with rose bengal as a photosensitizer, triethanolamine (TEA) as an electron donor, and Pt as a cocatalyst, has been reported Under visible light irradiation (λ ≥ 420 nm), the highest rate of hydrogen evolution and apparent quantum efficiency are about 569 μmol h−1 and 113%, respectively According to the effects of urea and ionic strength on the activity of hydrogen evolution, the dimers of rose bengal play a significant role in the photosensitized hydrogen evolution process On the basis of activity tests and UV−vis absorbance and fluorescence measurements, the probable mechanism for photosensitized hydrogen evolution has been postulated

Efficient Photocatalytic Hydrogen Evolution from Water without an Electron Mediator over Pt-Rose Bengal Catalysts

The readily obtained noble-metal-free molecular catalyst systems, with xanthene dyes (Rose Bengal, RB2–; Eosin Y, EY2–; and Eosin B, EB2–) as photosensitizers, [Co(bpy)3]Cl2 as catalyst, and triethylamine as sacrificial electron donor, are highly active for visible-light-driven (λ > 450 nm) hydrogen production from water. The turnover frequency is up to 54 TON/min versus RB2– with a RB2–/[Co(bpy)3]Cl2 molar ratio of 1:10 in CH3CN/H2O under optimal conditions in the first half hour of irradiation (λ > 450 nm), and the turnover number is up to 2076 versus RB2–. Comparative studies show the following: (1) The photocatalytic H2-evolving activity of the cationic cobalt complex [Co(bpy)3]Cl2 is apparently higher than the neutral cobaloxime complexes with xanthene dyes as potosensitizers, and also much higher than the analogous system of [Ru(bpy)3]Cl2/[Co(bpy)3]Cl2. (2) The UV–vis absorptions of xanthene dyes are red-shifted to different extents upon addition of [Co(bpy)3]Cl2 to the aqueous or CH3CN/H2O solution...

Promoting Effect of Electrostatic Interaction between a Cobalt Catalyst and a Xanthene Dye on Visible-Light-Driven Electron Transfer and Hydrogen Production

Photosensitized reduction of water to hydrogen using novel Maya blue-like organic-inorganic hybrid material.

The effect of the composition of five xanthene dyes (photoabsorber and photosensitizer) on the hydrogen photoproduction from aqueous solutions was investigated. It is suggested that triethanolamine (TEOA) can quench the excited singlet state of fluorescein in aqueous solution (1 × 10−4 mol l−1, pH 12.5). As a result, a reduced form of fluorescein is produced, which can further reduce H+ to H2 in the presence of K2PtCl6 (5 × 10−5 mol l−1). The quantum yield of H2 photoproduction (ΦH2) is 0.024. For tetraiodofluorescein (erythrosin) in aqueous solution (1 × 10−4 mol l−1), pH 12.5; K2PtCl6, 5 × 10−5 mol l−1), ΦH2 is as high as 0.30 owing to the inner molecular heavy atom effect. The quantum yields of fluorescence and intersystem crossing, ΦF and ΦISC, were measured and compared with ΦH2 for all the investigated dyes. The results show an important ability of xanthene dyes to enhance hydrogen photoproduction from alkaline aqueous solutions.

Qing-Shan Xie

Papers

Photochemical hydrogen evolution from alkaline solutions of xanthene dyes