I. Kulszewiczbajer et al., PROTONATION OF POLYANILINE IN HEXAFLUORO-2-PROPANOL - SPECTROSCOPIC INVESTIGATION, Macromolecules, 30(23), 1997, pp. 7091-7095
Three principal forms of polyaniline, leucoemeraldine (ZEE), emeraldin
e (EB), and pernigraniline (PNB), have been prepared, and their spectr
al properties have been studied in a newly discovered polyaniline solv
ent, hexafluoro 2-propanol (HFIP). In HFIP a significant hypsochromic
shift of the absorption due to main electronic transitions is observed
with respect to the analogous transitions in the spectra recorded for
N-methylpyrrolidinone (NMP). In particular, the pi to pi transition
is shifted to 308 nm in LEE and to 305 nm in EB and PNB and the benzoi
d to quinoid ring excitonic transition is shifted to 502 nm in EB and
PNB. In EB and PNB spectra, an additional peak at 800 nm is observed,
which can be ascribed to the protonation of these forms of polyaniline
by the highly acidic solvent. EB has been protonated in HFIP solution
with three types of protonating agents: camphorsulfonic acid (CSA), p
henylphosphonic acid (PPA), and poly(hexamethylene phosphate) (PHMeP).
Protonation in HFIP facilitates the formation of the extended coil co
nformation of emeraldine similarly to the protonation in m-cresol. The
extended coil conformation favors in turn the delocalization of polar
ons. The degree of polaron delocalization, as judged from UV-vis-NIR s
pectra, depends strongly on the protonation agent, the highest delocal
ization being observed for EB(PPA)(y).