Tuning of the emission
within the near-infrared to visible range
is observed in
p
-toluenesulfonic acid-doped polyaniline
light emitting diodes (PANI/PTSA), when water molecules are absorbed
by the active material (wet PANI/PTSA). This is a hybrid material
that combines a conjugated π-electron system and a proton system,
both strongly interacting in close contact with each other. The proton
system successfully competes with the electron system in excitation
energy consumption (when electrically powered), thanks to the inductive
resonance energy transfer from electrons to protons in wet PANI/PTSA
at the energy levels of combination of vibrations and overtones in
water, with subsequent light emission. Wet PANI/PTSA, in which electrons
and protons can be excited parallelly owing to fast energy transfer,
may emit light in different ranges (on a competitive basis). This
results in intense light emission with a maximum at 750 nm (and the
spectrum very similar to that of an excited protonic system in water),
which is blue-shifted compared to the initial one at ∼850 nm
that is generated by the PANI/PTSA dry sample, when electrically powered.