The fundamental Fuzzy logic operators and some complex boolean logic circuits implemented by the chromogenism of a spirooxazine.

1,3-Dihydro-1,3,3-trimethyl-8'-nitro-spiro[2H-indole-2,3'-[3H]naphth[2,1-b][1,4]oxazine] (SpO) is a photochromic, acidichromic and metallochromic compound. Its chromogenic properties are characterized in acetonitrile, at room temperature. They are exploited to process both boolean and Fuzzy logic. By using HClO(4), AlCl(3) and Cu(ClO(4))(2) as chemical inputs, UV radiation as power supply, and the absorbance at specific wavelengths in the visible as optical output, SpO results in a five-states molecular switch whereby some complex boolean logic circuits are implemented. If the chemical inputs are varied in an analog manner, the solution of SpO assumes an infinite number of colours. Therefore, by choosing the RGB colour coordinates as optical outputs, the fundamental operators of the "infinite-valued" Fuzzy logic are implemented. Particularly, two Fuzzy logic systems are built upon a new defuzzification procedure imitating the way humans perceive colours.