4 research outputs found
Oligothiophene Nanoparticles: Photophysical and Electrogenerated Chemiluminescence Studies
Thiophene oligomer nanoparticles (NPs) were studied by
fluorescence
spectroscopy and electrogenerated chemiluminescence (ECL). Distinct
spectroscopic differences between aggregates or NPs of thiophene hexamers
having differing substitution patterns of solubilizing alkyl groups
were observed. The α,ω-unsubstituted thiophene hexamer, <b>Hexamer-2</b>, exhibited fluorescence properties that were similar
in solution and as colloidal NPs; there was only a small red shift
compared with what was observed for the discrete system dissolved
in tetrahydrofuran (THF). In contrast, the oligomer substituted in
the α,ω-positions with branched alkyl substituents (<b>Hexamer-1</b>) displayed a gradual bathochromic shift of the fluorescence
maximum in proportion to the amount of a poor solvent (water) added
to the THF solution. Moreover, the fluorescence characteristics for
the oligomer(s) dissolved in a mixture of THF and water were similar
to those seen by annihilation ECL in a mixture of benzene/acetonitrile.
On this basis, we conclude that annihilation ECL may be a useful technique
for monitoring the formation of organic nanoparticles
Spectral Dependence of the Internal Quantum Efficiency of Organic Solar Cells: Effect of Charge Generation Pathways
The
conventional picture of photocurrent generation in organic
solar cells involves photoexcitation of the electron donor, followed
by electron transfer to the acceptor via an interfacial charge-transfer
state (Channel I). It has been shown that the mirror-image process
of acceptor photoexcitation leading to hole transfer to the donor
is also an efficient means to generate photocurrent (Channel II).
The donor and acceptor components may have overlapping or distinct
absorption characteristics. Hence, different excitation wavelengths
may preferentially activate one channel or the other, or indeed both.
As such, the internal quantum efficiency (IQE) of the solar cell may
likewise depend on the excitation wavelength. We show that several
model high-efficiency organic solar cell blends, notably PCDTBT:​PC70BM
and PCPDTBT:​PC60/70BM, exhibit flat IQEs across the visible
spectrum, suggesting that charge generation is occurring either via
a dominant single channel or via both channels but with comparable
efficiencies. In contrast, blends of the narrow optical gap copolymer
DPP-DTT with PC70BM show two distinct spectrally flat regions in their
IQEs, consistent with the two channels operating at different efficiencies.
The observed energy dependence of the IQE can be successfully modeled
as two parallel photodiodes, each with its own energetics and exciton
dynamics but both having the same extraction efficiency. Hence, an
excitation-energy dependence of the IQE in this case can be explained
as the interplay between two photocurrent-generating channels, without
recourse to hot excitons or other exotic processes
Ion-Regulated Allosteric Binding of Fullerenes (C<sub>60</sub> and C<sub>70</sub>) by Tetrathiafulvalene-Calix[4]pyrroles
The
effect of ionic species on the binding of fullerenes (C<sub>60</sub> and C<sub>70</sub>) by tetrathiafulvalene-calix[4]Âpyrrole
(TTF-C4P) receptors and the nature of the resulting supramolecular
complexes (TTF-C4P + fullerene + halide anion + tetraalkylammonium
cation) was studied in the solid state through single crystal X-ray
diffraction methods and in dichloromethane solution by means of continuous
variation plots and UV–vis spectroscopic titrations. These
analyses revealed a 1:1 stoichiometry between the anion-bound TTF-C4Ps
and the complexed fullerenes. The latter guests are bound within the
bowl-like cup of the C4P in a ball-and-socket binding mode. The interactions
between the TTF-C4P receptors and the fullerene guests are highly
influenced by both the nature of halide anions and their counter tetraalkylammonium
cations. Three halides (F<sup>–</sup>, Cl<sup>–</sup>, and Br<sup>–</sup>) were studied. All three potentiate the
binding of the two test fullerenes by inducing a conformational change
from the 1,3-alternate to the cone conformer of the TTF-C4Ps, thus
acting as positive heterotropic allosteric effectors. For a particular
halide anion, the choice of tetraalkylammonium salts serves to modulate
the strength of the TTF-C4P-fullerene host–guest binding interactions
and, in conjunction with variations in the halide anion, can be exploited
to alter the inherent selectivity of the host for a given fullerene.
Differences in binding are reflected in the excited state optical
properties. Overall, the present four-component system provides an
illustration of how host–guest binding events involving appropriately
designed artificial receptors can be fine-tuned via the addition of
simple ionic species as allosteric modulators
Exploration of a Series of 5‑Arylidene-2-thioxoimidazolidin-4-ones as Inhibitors of the Cytolytic Protein Perforin
A series of novel 5-arylidene-2-thioxoimidazolidin-4-ones
were
investigated as inhibitors of the lymphocyte-expressed pore-forming
protein perforin. Structure–activity relationships were explored
through variation of an isoindolinone or 3,4-dihydroisoquinolinone
subunit on a fixed 2-thioxoimidazolidin-4-one/thiophene core. The
ability of the resulting compounds to inhibit the lytic activity of
both isolated perforin protein and perforin delivered in situ by natural
killer cells was determined. A number of compounds showed excellent
activity at concentrations that were nontoxic to the killer cells,
and several were a significant improvement on previous classes of
inhibitors, being substantially more potent and soluble. Representative
examples showed rapid and reversible binding to immobilized mouse
perforin at low concentrations (≤2.5 μM) by surface plasmon
resonance and prevented formation of perforin pores in target cells
despite effective target cell engagement, as determined by calcium
influx studies. Mouse PK studies of two analogues showed <i>T</i><sub>1/2</sub> values of 1.1–1.2 h (dose of 5 mg/kg iv) and
MTDs of 60–80 mg/kg (ip)