A comparison of experimental and theoretical studies of benzoquinone modified poly(thiophene): effect of polymerization techniques on the structure and properties

The present manuscript reports the synthesis of benzoquinone (BQ) modified polythiophene (PTh) by chemical and microwave-assisted polymerization techniques. The synthesized oligomers were investigated for their spectral, morphological and thermal properties via FTIR, UV-visible, scanning electron microscopy (SEM) and thermogravimetric (TGA) analyses. Theoretical calculations were performed by using Gaussian 09 software via the DFT/B3LYP method with the 6-311G basis set. FTIR confirmed the formation of hydroquinone modified PTh when the polymerization was carried out by magnetic stirring and ultrasonication, while the formation of BQ modified PTh was obtained by microwave irradiation. The electronic transitions obtained via experimental UV-visible studies were also found to be in close agreement with the theoretical spectra. SEM revealed a well-formed morphology comprising needle shaped rods for the oligomer synthesized under microwave irradiation. The TGA-DTA studies revealed low char content for the above oligomer, while the florescence studies revealed intense emission around 450 nm. The highest quantum yield was found to be 0.024, which also showed high singlet oxygen generation tendency as well as a high single oxygen quantum yield of 0.30 and could be utilized to design imaging probes applicable in photodynamic therapy.

The present manuscript reports the synthesis of benzoquinone (BQ) modified polythiophene (PTh) by chemical and microwave-assisted polymerization techniques.

Low bandgap poly(thienylenemethine) derivatives bearing terarylene moieties in the side chains

Novel low bandgap poly(thienylenemethine) derivatives bearing terphenylene moieties in the side chains were synthesised. The bandgaps were controlled by introducing quinoidal structures into the benzonoidal main chains.

Anthraquinone-based discotic liquid crystals

The syntheses of six room-temperature discotic liquid crystals based on an alkoxy-anthraquinone (AQ) framework is described. Differential scanning calorimetry, X-ray diffraction (XRD), and cross-polarized microscopy were used to identify phases and confirm phase-transition temperatures. Cross-polarized microscopy results suggest columnar discotic structures at room temperature. However, the AQ derivatives also undergo mesophase-to-mesophase transitions, which are attributed to rectangular- to hexagonal-columnar discotic transitions based on XRD analysis. Furthermore, some of the compounds display remarkable liquid crystalline phase stability that spans from -50 to 150 degrees C, a useful temperature range for organic materials applications. The different AQ derivatives did not exhibit electronic perturbations, as all compounds have absorption onsets of approximately 400 nm. Finally, solution cyclic voltammetry of the AQ derivatives was carried out to determine the redox potentials, diffusion coefficients, and electron transfer rate constants. All AQ derivatives had E(1/2) values that ranged between -1.52 and -1.70 V vs Fc/Fc(+). Diffusion coefficients and electron transfer rates for all AQ derivatives ranged between 0.4 and 7.1 x 10(-6) cm(2) x s(-1) and 0.9 and 5.2 x 10(-3) cm x s(-1), respectively.

Beta-substituted terthiophene [2]rotaxanes

Two kinds of beta-substituted terthiophene [2]rotaxanes were synthesized using the host-guest pairs of the electron-deficient cyclophane cyclobis(paraquat-p-phenylene) (CBPQT(4+)) and the electron-rich terthiophenes with diethyleneglycol chains at the beta-position. One is made from the alpha-position non-substituted terthiophene (3 T-beta-Rx) and the other is made from the alpha-dibromo-substituted terthiophene (3 TBr-beta-Rx). The binding constants of the beta-substituted terthiophene threads were confirmed to be smaller than that of the alpha-substituted terthiophene analogue. By UV/Vis absorption measurements, we confirmed the charge-transfer (CT) band in the visible region with an extinction coefficient of approximately 10(2) (M(-1) cm(-1)). Strong, but not quantitative, quenching of the terthiophene fluorescence was confirmed for the [2]rotaxanes. Although the beta-substituted terthiophene thread was electrochemically polymerizable, the [2]rotaxane 3 T-beta-Rx was not polymerizable. This result indicates that the interlocked CBPQT(4+) macrocycle effectively suppresses the electrochemical polymerization of the terthiophene unit because electrostatic repulsive and steric effects of CBPQT(4+) hinder the dimerization of the terthiophene radical cations. In the electrochemical measurement, we confirmed the shift of the first reduction peak towards less negative potential compared to free CBPQT(4+) and the splitting of the second reduction peak. These electrochemical behaviors are similar to those observed for the highly-constrained [2]rotaxanes. The beta-substituted terthiophene [2]rotaxanes reported herein are important key compounds to prepare polythiophene polyrotaxanes.

Long-lived photoinduced charges in donor-acceptor anthraquinone-substituted thiophene copolymers

The photoinduced charge-transfer properties of a series of polyalkylthiophene copolymers, carrying anthraquinone substituents covalently linked to the conjugated backbone, have been studied in the solid state by photoinduced absorption (PA) and light-induced electron spin resonance (LESR) spectroscopy. The measurements indicate the formation of metastable charges arising from the photoinduced electron transfer from the polythiophene backbone to the anthraquinone moieties. At low temperatures (below 200 K), long-lived persistent charges are formed, exhibiting lifetimes that extend for several minutes; their recombination kinetics has been studied by following the formation and decay of the PA and LESR signals. The results are rationalized using a model originally proposed to describe the low-temperature recombination kinetics of long-lived photoexcited carriers in amorphous inorganic semiconductors. It is clearly evidenced that, in these polymers, the number of acceptor substituents in the chain, easily tuned by chemical tailoring, plays a key role in the photoexcitation scenario.

Incorporation of fused tetrathiafulvalenes (TTFs) into polythiophene architectures: varying the electroactive dominance of the TTF species in hybrid systems

A novel polythienylenevinylene (PTV) and two new polythiophenes (PTs), featuring fused tetrathiafulvalene (TTF) units, have been prepared and characterized by ultraviolet-visible (UV-vis) and electron paramagnetic resonance (EPR) spectroelectrochemistry. All polymers undergo two sequential, reversible oxidation processes in solution. Structures in which the TTF species is directly linked to the polymer backbone (2 and 4) display redox behavior which is dictated by the fulvalene system. Once the TTF is spatially removed from the polymer chain by a nonconjugated link (polymer 3), the electroactivity of both TTF and polythiophene moieties can be detected. Computational studies confirm the delocalization of charge over both electroactive centers (TTF and PT) and the existence of a triplet dication intermediate. PTV 4 has a low band gap (1.44 eV), is soluble in common organic solvents, and is stable under ambient conditions. Organic solar cells of polymer 4:[6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) have been fabricated. Under illumination, a photovoltaic effect is observed with a power conversion efficiency of 0.13% under AM1.5 solar simulated light. The onset of photocurrent at 850 nm is consistent with the onset of the pi-pi absorption band of the polymer. Remarkably, UV-vis spectroelectrochemistry of polymer 4 reveals that the conjugated polymer chain remains unchanged during the oxidation of the polymer.