Detail Photophysical Studies of Sulfonated Polyaniline in Aqueous Medium.

Sulfonated polyaniline (SPANI) has emerged as a promising polymer in the past few decades due to its solubility in water and relatively moderate conductivity. However, to date, literature data on the optical characterization of SPANI are very limited and preliminary in nature. In the present work, SPANI is synthesized by direct sulfonation of emeraldine salt form of polyaniline with chlorosulfonic acid in an inert solvent. Detail photophysical properties of SPANI are investigated in aqueous medium by using steady state (concentration, temperature, pH, and excitation wavelength dependence) and time-resolved spectroscopic techniques. The steady state fluorescence emission measurements are carried out carefully to avoid inner filter effect (especially secondary inner filter effect or reabsorption effect) as well as scattering. Two ground state conformations of SPANI are suggested to exist in aqueous medium. Excitation wavelength dependence of the fluorescence emission spectra is attributed to red-edge effect. All these observations are nicely corroborated by the fluorescence lifetime data of SPANI obtained from time-resolved measurements. All these new findings are extremely important in view of the potential applications of SPANI in polymer optoelectronics.