Synthesis and properties of ionic conjugated polymer with spiroxazine moiety

A noble conjugated ionic polymer with photochromic spiroxazine moiety, poly[2-ethynyl-N-hexyloxyspiroxazine pyridinium bromide] (PEHSPB) 6 was prepared by the activated polymerization of 2-ethynylpyridine 5 with 1,3,3-trimethyl-6′-bromohexyloxyspiro[2H]-indol-2,3′-[3H]-naphth[2,1-b][1,4]oxazine 4 without any additional initiator or catalyst. The polymerization reaction was performed in DMF solvent at the temperature of 120 °C. As the polymerization proceeded, the reaction solution became more viscous and black in colour. The polymer yield and inherent viscosity were 75% and 0.15 dL/g, respectively. The instrumental analysis data on the chemical structure of PEHSPB 6 indicated that the present PEHSPB 6 have a conjugated polymer backbone system with the spiroxazine-hexyl substituents. X-ray diffraction analyses of the polymers indicated that the present polymers are mostly amorphous. The photoluminescence peak is located at 515 nm corresponding to the photon energy of 2.41 eV. Upon UV irradiation, closed spiroxazine form is transformed into the open merocyanine form that reverts back to the colourless spiro form in dark.