PHOTOINDUCED PROTONATION OF AZO DYES IN HALOGENATED SOLVENTS AND POLYMERS

We show that protonation and/or photocyclisation of azo dye molecules, which are often used as chromophores for applications in non-linear o ptics, can be induced by optical irradiation either in solution or in polymer films. irradiation causes dissociation of halogenated solvents or polymers, generating an acid which then protonates the dye molecul e. In guest-host polymer systems consisting of azo dyes in halogenated polymers this type of protonation is shown also to result from the ap plication of an electric field during the poling required for second-o rder applications. In both halogenated and non-halogenated systems a r elatively slow bleaching process has been observed and attributed to p hotoinduced 6pi-cyclisation of the azo dye. We investigate the conditi ons under which protonation or cyclisation of azobenzenes occurs and i dentify the form of the protonated molecule.