We describe the photochemical behavior of aqueous solutions containing the Co(CN) 6 3complex ion and the trans-chalcone form Ct of the 4′-methoxyflavylium ion (AH + ). It is shown that, under the experimental conditions used, the photochemical reaction leading from Ct to AH + shows an off-on-off behavior upon excitation with a continuous light source or with successive light flashes. The described systems perform as threshold devices and as XOR (eXclusive OR) logic gates. They behave as rudimental artificial neuron-like systems in the sense that their outputs (formation of the AH + species, with a consequent change in the spectroscopic properties) are the result of an elaboration of two distinct (light) inputs by chemical reactions in solution.
Tetra-peri-(tert-butyl-benzo)-di-peri-(pyrimidino)-coronene 1, the parent compound of the nitrogen heterosuperbenzene family N-HSB, is employed as a novel monotopic ligand in the formation of [Pd(η 3 -C3H5)(1)]PF6 2 and [Ru(bpy)2(1)](PF6)2 (where bpy ) 2,2′-bipyridine 3a and d8-2,2′-bipyridine 3b). These N-coordinated complexes are fully characterized by 1 H NMR and IR spectroscopy and ESI-MS. Metal coordination has a profound effect on both the absorption and the emission properties of 1. Pd(II) coordination causes a red-shift in the low-energy absorptions, a decrease in the intensity of the n-π* absorptions, and a quenching of the emission. Ru(II) coordination causes absorption throughout the visible region and creates two new complexes that join an elite group of compounds known as "black" absorbers. 3a and 3b possess two discernible 1 MLCT bands. The one of exceptionally low energy (λmax ) 615 nm) has an associated 3 MLCT emission (λmax ) 880 nm) due to the unprecedented electron delocalization and acceptor properties of the rigid aromatic N-HSB 1. Both Ru(II) complexes are near-IR emitters with unusually protracted emission lifetimes of 320 ns at 77 K. They are photochemically inert, and their electrochemical properties are consistent with the presence of a low-lying π* orbital on 1. The first two reversible reductions (E1/2 (CH3CN), -0.54 V, -1.01 V vs SCE) are due to the stepwise reduction of 1 and are anodically shifted as compared to [Ru(bpy)3] 2+ . Temperature-and concentration-dependent NMR studies on 2 and 3a suggest extensive aggregation is occurring in solution.
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