In this study, we report a preparation and an aggregate emission behavior of an amphiphilic donor-acceptor dye, which is composed of a triphenylamine-benzothiadiazole donor-acceptor chromophore and two water-soluble hexa(ethylene glycol) chains. The dye is strongly fluorescent in nonpolar solutions such as cyclohexane and toluene, whereas the emission intensity is reduced in aprotic polar solutions such as DMF and acetonitrile. This fluorescence reduction correlates with the increase in polarity, by which the transition from a local excited state to a highly polarized excited state is facilitated, leading to an increased nonradiative deactivation rate. Furthermore, significant fluorescence quenching is observed in protic polar solutions such as ethanol and methanol. Hydrogen-bonding interactions between the dye and the protic solvent molecules further accelerate the deactivation rate. In contrast, in a water solution, red light emission is achieved distinctly at 622 nm with a relatively large fluorescence quantum yield of 0.20. This red emission is related to the aggregation of the dye molecules grown in water. The kinetic analysis from the fluorescence rate constant and nonradiative rate constant indicates that the nonradiative deactivation channel is restricted in water. The formed aggregate, which was indicated by transmittance electron microscopy as a spherical aggregate morphology with a diameter of 3-4 nm, provides a less polar hydrophobic space inside the aggregate structure, by which hydrogen-bonding and the subsequent quenching are restricted, leading to the reduction of the nonradiative deactivation rate.
High functional group compatibility
of iridium-catalyzed synthesis
of enamines from amides and 1,1,3,3-tetramethyldisiloxane (TMDS) realized
facile access of a series of donor (D)−π–acceptor
(A)-conjugated enamines, in which enamine behaves as a donor functional
group. The amide precursors containing reducible functional groups,
such as halogen, carbonyl, and nitro groups, underwent reaction with
TMDS to give the corresponding enamines in high yields. In most cases,
chemoselective hydrosilane reduction of the amide group occurred while
other reducible groups remained intact. Absorption and emission properties
including solvatochromic behavior for the resulting D−π–A-conjugated
enamines were determined using UV–visible and fluorescent spectra,
which provided an understanding of the donor properties of the CHCHNPh2 group and photofunctional properties of the D−π–A
conjugated enamines as a fluorescent dye. Maximum absorption wavelength
(λabs) of p-ZC6H4CHCHNPh2 was predictable from λabs of p-ZC6H4NPh2, which was supported by density functional theory calculations.
Some of the D−π–A-conjugated enamines showed fluorescence
with moderate fluorescence quantum yields (Φfl).
Of interest are unusually emissive π-conjugated enamines containing
a nitro group, which generally behaves as strong quenchers of fluorescence.
The additive effect of B(C6F5)3 resulted
in significant red shifts of λabs and λfl. In some cases, high Φfl was observed in
the solution state.
The performance of bulk heterojunction (BHJ) organic photovoltaics (OPVs) based on an amorphous polymer, poly(3HTBT-TPA), and fabricated using either halogenated or non-halogenated solvents was investigated. All the BHJ OPVs exhibited almost the same power conversion efficiencies of around 2.2%, indicating that their performance is independent of the casting solvent. These experimental results indicate that the use of amorphous π-conjugated polymers in the fabrication of BHJ OPVs offers two advantages over the use of polycrystalline π-conjugated polymers: highly reproducible OPV performance and the possibility of an environmentally friendly process for fabricating OPVs.
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