PHOTOINDUCED HYDROGEN-PRODUCTION IN DILUTE-SOLUTIONS AND ORGANIZED ASSEMBLIES

A new class of covalently linked cyanine dye-electron relay compounds have been investigated. As well as dro-chinolinyliden-(2)-methyl]-1-et hyl-chinolinium chloride (1), nolinium-1-yl]propyl]-1'-methyl-4,4'-bi- pyridinium trichloride (2) and inolinium-1-yl]pentyl]-1'-methyl-4,4'-b ipyridinium triiodide (3) were able to form huge molecular associates with a well-defined three-dimensional structure in dilute, aqueous sol utions (critical gel concentration c(crit) > 2 x 10(-3) mol l-1). Phot ochemical properties of compounds (1) (3) were different in gels and i n solutions (c < c(crit)) without organized dye associates. Owing to a ntenna effects, organized assemblies provide an intense light harvesti ng effect. Covalently linked viologen groups quench the excited dye in tramolecularly with a higher efficiency. Furthermore, the increased qu enching efficiency was found to be dependent on the degree of organiza tion. In dilute aqueous solutions (c < c(crit), lambda(EX) > 280 nm), compounds (1)-(3) could act as photosensitizers for light-induced hydr ogen production (via intermolecular charge separation) with quantum yi elds of phi1/2H-2 = 2%. In organized assemblies (C > C(crit)), intramo lecular charge separation [in compounds (2) and (3)] could be observed and hydrogen production experiments were performed successfully.