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

Major, Máté M. and Horváth, Ottó and Fodor, Melinda A. and Fodor, Lajos and Valicsek, Zsolt and Grampp, Günter and Wankmüller, Alexander (2016) Photophysical and photocatalytic behavior of nickel(II) 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)porphyrin. Inorganic Chemistry Communications, 73. pp. 1-3. ISSN 1387-7003

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Abstract

Kinetically inert cationic Ni(II)TMPyP4+ (H2TMPyP4+ = 5,10,15,20-tetrakis(methylpyridinium-4-yl)porphyrin) displayed a characteristic fluorescence (τ = 1.2-1.4 ns, Φ = 2.0×10-3), 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 dinamically quench the triplet excited state of Ni(II)TMPyP4+ (τ = 6.31 μs), hence no reduction of the metal center occured upon irradition. Instead, in the presence of this electron donor (at 1×10-3M) the excited-state lifetime dramatically increased (to τ = 36.6 μs), indicating the formation of a Ni(II)TMPyP4+-TEOA associate. This longer-lived triplet was efficiently quenched by MV2+ (kq = 9.9×106 M-1s-1), leading to the formation of MV●+. The overall quantum yield of this one-step photoassisted electron transfer is considerably high (Φ = 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.

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