We describe the photochemical behavior of aqueous solutions containing the
Co(CN)(6)(3-) complex ion and the trans-chalcone form Ct of the 4'-methoxyf
lavylium ion (AH(+)). It is shown that, under the experimental conditions u
sed, the photochemical reaction leading from Ct to AH(+) shows an off-on-of
f behavior upon excitation with a continuous light source or with successiv
e 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(+) speci
es, with a consequent change in the spectroscopic properties) are the resul
t of an elaboration of two distinct (light) inputs by chemical reactions in
solution.