Ultrafast photophysical studies of sulfonated polyaniline in aqueous medium by femtosecond transient absorption spectroscopy

In our previous work (Khatun et al., J. Phys. Chem. A 122 (2018) 7089-7098), synthesis and characterization of sulfonated polyaniline (SPANI) were discussed. Photophysical properties of SPANI in aqueous medium were also investigated using steady state spectroscopic techniques, which suggested the co-existence of two conformations (‘A’ and ‘B’) of SPANI in the normal working low acidic medium. Also, combined red-edge effect was observed from the two conformations of SPANI in aqueous medium. In the present work, a detailed investigation is carried out on the ultrafast photophysical properties of SPANI in aqueous medium by employing femtosecond transient absorption spectroscopy based on pump-probe technique. It is found that excited state absorption from the S1 state of SPANI in aqueous medium to higher electronic states originates mostly due to the conformation ‘A’ in the whole spectral range and very weakly due to the conformation ‘B’ on the blue side of the spectra. These new findings are extremely important keeping in mind various potential applications of SPANI in the field of polymer optoelectronics.