la6b03618_si_001.pdf (1.17 MB)
Organic Ion-Pair Charge-Transfer (IPCT) Nanoparticles: Synthesis and Photoinduced Electrochromism
journal contribution
posted on 2016-12-13, 00:00 authored by Hiroshi Yao, Tomoki EnsekiWe
report fabrication of photoinduced-electrochromic (or photochromic)
organic nanoparticles that can be regarded as a new class of photoswitchable
nanomaterials. Ion association between dicationic benzyl viologen
(BzV2+) and tetraphenylborate anion (TPB–) in water produces organic ion-pair charge-transfer-type (IPCT)
nanoparticles with a mean diameter of 15–20 nm. Electrostatic
binding of BzV2+ with TPB– results in
the prominent appearance of a new broad absorption band at 400–550
nm, which can be assign to the CT transition between these species.
The IPCT nanoparticles show an interesting photoinduced electrochromic
behavior caused by the electron transfer (ET) from TPB– to BzV2+, giving an intense blue-color dispersion. The
feed charge stoichiometry (= [TPB–]/(2 × [BzV2+])) does not influence the kinetics of the photoinduced electrochromism,
but it remarkably controls the reverse ET reaction (or retention time)
in the nanoparticles; in the case of neutral stoichiometry, a very
long-lived ET state can be observed, which is mainly due to decomposition
of the oxidized TPB (sacrificial donor) and the resultant absence
of the counterpart of benzyl viologen radical cations (BzV+•) for back ET reaction. On the other hand, the excess presence
of TPB– does not cause the decomposition of oxidized
TPB in the nanoparticle, making the reverse ET reaction faster, but
a moderately long-lived ET state is still observable, which is probably
originated from efficient electron diffusion or transport between
molecules inside the nanoparticle.