PhotophySical and photocatalytic behavior of nickel(II) 5,10,15,20-tetrakis (1-methylpyridinium-4-yl)porphyrin

Kinetically inert cationic Ni(II)TMPyP4+ (H2TMPyP4+ = 5,10,15,20-tetrakis(methylpyridinium-4-yl)porphyrin) displayed a characteristic fluorescence (tau = 1.2-1.4 ns, Phi = 2.0 x 10(-3)), which was quenched with triethanolamine (TEOA) in a static way. This complex proved to be an efficient photocatalyst in the system containing TEOA and methylviologen (MV2+) as electron donor and acceptor, respectively. Interestingly, however, deviating from the behavior of the analogous Co(III) and Mn(III) complexes in such a system, TEOA did not dynamically quench the triplet excited state of Ni(II)TMPyP4+ (tau = 6.31 mu s), hence no reduction of the metal center occured upon irradiation. Instead, in the presence of this electron donor (at 1 x 10(-3) M) the excited-state lifetime dramatically increased (to tau = 36.6 mu s), indicating the formation of a Ni(II)TMPyr(4+)-TEOA associate. This longer lived triplet was efficiently quenched by MV2+ (k(q) = 9.9 x 10(6) M-1 s(-1)), leading to the formation of MV center dot+. The overall quantum yield of this one-step photoassisted electron transfer is considerably high (Phi = 0.011-0.013 at Soret-band irradiation). Hence, this system, combined with a suitable co-catalyst, may be applicable for visible light-driven hydrogen generation from water. (C) 2016 Elsevier B.V. All rights reserved.