Dating from the earliest work on the light-driven generation of H 2, the photosensitizer has most often been a Ru(II) complex with 2,2′-bipyridine (bpy) and/or related heterocyclic ligands having a long-lived triplet metal-to-ligand charge transfer state (3 MLCT) (5, 7, 30–33).
In this paper, we focus on efforts dealing with the light-driven generation of H 2, which in its simplest form requires a light absorber or photosensitizer (PS) for electron-hole creation, a means or pathway for charge separation and electron transfer, an aqueous proton source, a catalyst for collecting electrons and protons and promoting their conversion to H 2, and an ultimate source of electrons in the form of an electron donor. Whereas some of these studies date back more than 30 y (14–22), recent progress on each half-reaction has been notable, particularly with regard to catalyst development and mechanistic understanding of each transformation (6, 23–29). As a redox reaction, water splitting has been studied primarily in terms of its two half-reactions, the reduction of aqueous protons to H 2 and the oxidation of water to O 2 (2–13). photochemistry | solar energy conversion | hydrogen | spectroscopy | synthesis W ater splitting into hydrogen and oxygen is the key energy-storing reaction of artificial photosynthesis (AP) and one of the most promising long-term strategies for carbon-free energy on a potentially global scale (1). It is found that upon 530 nm irradiation in a H 2 O solution (pH 4) with ascorbic acid as an electron donor, the dyad linked to Pt-TiO 2 via a phosphonate or carboxylate attachment shows excellent light-driven H 2 production with substantial longevity, in which one particular dyad exhibits the highest activity, generating ∼40,000 turnover numbers of H 2 over 12 d (with respect to dye). For H 2 generation studies, the TiO 2 particles are platinized (Pt-TiO 2) so that the light absorber (the dyad), the electron conduit (TiO 2), and the catalyst (attached colloidal Pt) are fully integrated. Connection to TiO 2 nanoparticles is carried out by sonication leading to in situ attachment to TiO 2 without prior hydrolysis of the ester linking groups to acids. The absorption spectra and cyclic voltammograms of the dyads show that the spectroscopic and electrochemical properties of the dyads are the sum of the individual chromophores (Bodipy and the PtN 2 S 2 moieties), indicating little electronic coupling between them. Each of the new dyads contains either a bipyridine (bpy) or phenanthroline (phen) diimine with an attached functional group that is used for binding directly to TiO 2 nanoparticles, allowing rapid electron pho-toinjection into the semiconductor. In these dyads, the Bodipy dye is bonded directly to the ben-zenedithiolate ligand of the PtN 2 S 2 CT chromophore. New dyads consisting of a strongly absorbing Bodipy (dipyrrome-thene-BF 2) dye and a platinum diimine dithiolate (PtN 2 S 2) charge transfer (CT) chromophore have been synthesized and studied in the context of the light-driven generation of H 2 from aqueous protons. These results helps to understand the tuning of photoluminescence of GO and provide ideas to develop various optoelectronic materials such as light emitting diodes, luminescent bio-trackers etc. In view of the recently published data on the photoluminescence of GO, interaction with polymer by forming nano-composite, modulation of band gap by the surfactant and pH of the medium have been discussed to shed light on the tunable optical property of GO.
The present review aims to describe few selected themes of current interest dealing with tunable luminescence of GO by some external factors, e.g. The luminescence of GO can be utilized to produce optoelectronic devices, bio- analytical sensors, and bio-imaging setups. These type of functionalization leads to a finite band gap in GO and it exhibits interesting photoluminescence which is limited in graphene due to zero band gap. Presence of different type of oxygen containing functional groups produces structural defect in graphene. Graphene oxide (GO), a water soluble precursor for the synthesis of graphene, has drawn tremendous interest in modern science not only for its unique properties but also for the varieties of its applications.
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