Highly transparent photochromic gels in the visible region can be prepared by the incorporation of flavylium compounds in Pluronic matrixes (ABA-type tri-block copolymers composed of poly(ethylene oxide) (PEO) (A) and poly(propylene oxide) (PPO) units (B)). The chromophore 7-(N,N-diethylamino) 4-hydroxyflavylium switches from its yellow chalcone form to the red flavylium cation upon irradiation and reverts back to the chalcone form in the dark.
