SYNTHESIS OF 2,2' 5',2''-TERPYRIDINE AND 2,2'/5',2''/5'',2'''-QUATERPYRIDINE AND THEIR PHOTOCATALYSIS OF THE REDUCTION OF WATER/

2,2': 5',2''-Terpyridine (OPy-3) and 2,2':5',2'': 5'',2'''-quaterpyrid ine (OPy-4) are prepared by Ni-O-complex-catalysed polycondensation of 2,5-dichloropyridine in the presence of an excess of 2-chloropyridine . These two compounds show more efficient photocatalysis of H-2 evolut ion by the reduction of water than p-terphenyl and p-quaterphenyl in t he presence of triethylamine as an electron donor, and RuCl3 or K2PtCl 6 as a source of Ru-O or Pt-O colloids which function as an electron m ediator, The primary photochemical processes of OPy-n (n = 3 or 4) and the successive reactions have been investigated by gamma-radiolysis, pulse radiolysis and laser flash photolysis. The OPy-n molecules are c onverted to their anion radicals through reductive quenching of the ex cited states, A mechanism for the photocatalysis of hydrogen evolution is proposed in which the anion radicals supply electrons to protons o n the metal colloids. The anion radicals undergo protonation in compet ition with electron transfer, resulting in the loss of photocatalytic activity.