Many
donor–acceptor systems can undergo a photoinduced charge
separation reaction, yielding loose ion pairs (LIPs). LIPs can be
formed either directly via (distant) electron transfer (ET) or indirectly
via the dissociation of an initially formed exciplex or tight ion
pair. Establishing the prevalence of one of the reaction pathways
is challenging because differentiating initially formed exciplexes
from LIPs is difficult due to similar spectroscopic footprints. Hence,
no comprehensive reaction model has been established for moderately
polar solvents. Here, we employ an approach based on the time-resolved
magnetic field effect (MFE) of the delayed exciplex luminescence to
distinguish the two reaction channels. We focus on the effects of
the driving force of ET and the solvent permittivity. We show that,
surprisingly, the exciplex channel is significant even for an exergonic
ET system with a free energy of ET of −0.58 eV and for the
most polar solutions studied (butyronitrile). Our findings demonstrate
that exciplexes play a crucial role even in polar solvents and at
moderate driving forces, contrary to what is usually assumed.
A novel approach to the synthesis of polyaniline-montmorillonite (PANI-MMT) nanocomposites by in situ electropolymerization of anilinium-montmorillonite in 0.3 M sulfuric acid on a gold substrate is reported. The nanocomposites were characterized by elemental analysis, cyclic voltammetry, X-ray diffraction, in situ UV-vis spectroscopy, Fourier transform infrared spectroscopy, and in situ conductivity measurements. Cyclic voltammograms of PANI-MMT are similar to those of PANI synthesized electrochemically under similar conditions. Formation of PANI inside the MMT was confirmed by X-ray diffraction analysis where the d spacing is increased from 10.09 Å (Na + -montmorillonite) to 12.62 Å (PANI-MMT). The CsN stretching vibration (ν C-N ) which appears with PANI at 1296 cm -1 has been shifted to 1311 cm -1 for PANI-MMT, indicating the existence of interactions between intercalated PANI and MMT layers. Conductivities of the nanocomposites are almost an order of magnitude lower than those of PANI.
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