Awh Mau

XANTHENE DYES AS SENSITIZERS FOR THE PHOTOREDUCTION OF WATER

Abstract— Some photochemical and photophysical properties of a group of xanthene dyes have been studied in relation to their roles as sensitizers for the photoreduction of water. New spectroscopic and kinetic measurements have been carried out with these dyes. The triplet states of the dyes undergo energy‐transfer and electron‐transfer, but with rate constants differing by two orders of magnitude in favour of the former pathway. The very efficient transfer of triplet energy from a group of dyes to an acceptor molecule led to the design of a greatly improved system for the photochemical production of hydrogen.

PHOTOPRODUCTION OF HYDROGEN FROM LINKED CHROMOPHORES

Abstract On irradiation of solutions of anthryl‐substituted cobalt(III) cage complexes, [(l‐(anthryl‐9‐methylamino)‐8‐methyl‐3,6,10,13,16,19‐hexaazabicyclo [6.6.6] eicosane) cobalt(III)]3+ or [(l‐(4‐an‐thryl‐9)‐3‐aza‐butyl‐l‐amino)‐8‐methyl‐3,6,10,13,16,19‐hexaazabicyclo [6.6.6] eicosane)cobalt (III)]3* in the presence of ethylenediaminetetraacetic acid and platinum catalysts hydrogen was produced. These complexes act as coupled photosensitizers (anthracene moiety) and electron relays (cobalt cage) to produce H2via energy trapping and intramolecular electron transfer initially. The intensity of fluorescence and the photochemical reactivity favour the latter complex and the excited singlet state of the anthracene chromophore is invoked as the intermediate state leading to the reduction of Co(III) to Co(II).

Energy transfer between fluorescent dyes in alcohols and in nafion membranes

Abstract Singlet state energy transfer between proflavine (donor) and cresyl violet (acceptor) and between acridine orange (donor) and rhodamine B (acceptor) in alcohols and in Nafion (a perfluorosulfonated polymer membrane) has been investigated by steady-state and time-resolved fluorescence spectroscopy. In solution, the fluorescence decay profiles of the donor in the presence of acceptors are non-exponential but follow kinetics predicted from Forsters dipole-dipole model for energy transfer. The critical transfer distances obtained from the time-resolved experiments are in good agreement with the values calculated from spectral overlap data in solution. Higher energy transfer efficiencies than expected are observed for the dyes in Nafion membrane. The results suggest that dye molecules are heterogeneously distributed in the micelle-like polymer.

Fluorescence and photochemistry of dye sensitizers in nafion membrane

Abstract Methylene blue exhibits a higher fluorescence yield, longer fluorescence lifetime and a blue shift of the absorption spectrum in Nafion polymer membrane compared to an aqueous solution. The dye sensitized photooxidation of anthracene is also enhanced in the polymer. The results are discussed with reference to the heterogeneous microenvironment provided by the membrane structure.

Interaction of Cu2+ with ethanedioic acid bis-hydrazides

Abstract The chelating properties of oxalyl dihydrazide and a series of ethanedioic acid bis-hydrazides with Cu2+ in solution have been investigated by UV absorption and fluorescence quenching measurements. The UV absorption data indicate 1:1 complexation with equilibrium constants in the range Kc = 0·57 − 2·1 × 106 mol−1 for the bis-hydrazides and Kc = 8 × 104 mol−1 for oxalyl dihydrazide. The fluorescence quenching data for the 1-pyrenyl derivative confirm Cu2+ complexation. The relevance of these finds to the role of ethanedioic acid bis-hydrazides as Cu2+ chelating agents in polymers is discussed.