Chemically modified polyaniline (CMP) self doped derivatives were synthesised by the diazotisation of polyaniline, copolyanilines and polyaniline-Ti02 nanoparticle composites with diazonium salts and polymerising aniline diazo anilic or anthranilic dyes. Oxidative chemical polymerisation in strong acidic aqueous media with the help of (NH4)2S20a was employed to polymerise monomers or comonomers. The diazotisation of polyanilines was proved to be the most promising and efficient to incorporate sulphonic phenyl groups in polyanilines structure to form self doped CMPs. The highest degree of self doping! suiphonation was achieved when polyaniline- Ti02 composites were coupled with diazonium ion. CMPs were investigated with the help of analytical techniques such as UVVis, FT-IR, FT-NMR, fluorescence and elemental analysis. The spectroscopic and physical data confirm the introduction of chemically linked sulphonic phenyl groups and formation of triphenyl amine like fluorophores structures in them. They have the fundamental polyaniline properties as they are green in acidic and blue in basic media, pH sensitive, have reversible electrochromic and redox behaviour in different environments. They are highly fluorescent, soluble in polar solvents (H20, R-OH, NMP, DMSO, DMF) and optical metals ion sensor. Their solutions have persistent fluorescence even after several months without significant changes in their spectra. They can be immobilised directly and in the form of composites with other reagents such as PMMA, PVA, nafion and sol gel on glass and polymeric substrates. Their composite films are stable in ambient conditions and luminescent even after a period of one year. Their solubility, fluorescence and optical metals ion sensing are directly related to their degree of sulphonation! self doping. Consequently, SPPATi02 has better solubility, higher fluorescence intensity, stable optical pH response and lower limit of detection for Cu2+ ion compared to that of SPPA and SPCPA. Their UV-Vis absorption and emission spectra are pH sensitive with a linear and quick optical response in the range of pH 5-8. They have excitations at 256-258 and 292-300 nm in acidic and basic media respectively while emissions at 423- 428nm. They have broad optimum pH ranges (pH 6-10) for their emission and metal ions sensing. They can be used as pH sensor for a broad range of pH 3-8, out of which the optical sensitivity of pH 3-6 is based on hypo! hyper chromic effects in their fluorescence while of pH 5-8 in their UV-Vis absorption spectra. They are optical metals ions sensors for higher concentrations (> 10-4M) of heavy metals ion but are selective and sensitive to Cu2+ ion «10-4 M) lower concentrations. The optimum pH ranges for their optical Cu2+ ion sensing are broad (pH 6-10). Their LOO and LOa for Cu2+ ion on the basis of fluorescence quenching are in the ranges 3.96 x 10-7 - 4.5 x 10-7 and 1.3 x 10-6 - 1.5 x 10-6M respectively.