Alkyl Thiophene Research Articles

Thiophene π-bridge-based second near-infrared luminogens with aggregation-induced emission for biomedical applications.

In the past 5years, aggregation-induced emission luminogens (AIEgens) with emission in the second near-infrared (NIR-II) optical window have aroused great interest in bioimaging and disease phototheranostics, benefiting from the merits of deep penetration depth, reduced light scatting, high spatial resolution, and minimal photodamage. To construct NIR-II AIEgens, thiophene derivatives are frequently adopted as π-bridge by virtue of their electron-rich feature and good modifiability. Herein, we summarize the recent progress of NIR-II AIEgens by employing thiophene derivatives as π-bridge mainly compassing unsubstituted thiophene, alkyl thiophene, 3,4-ethylenedioxythiophene, and benzo[c]thiophene, with a discussion on their structure-property relationships and biomedical applications. Finally, a brief conclusion and perspective on this fascinating area are offered.

Influence of Donor Groups on Benzoselenadiazole-Based Dopant-Free Hole Transporting Materials for High Performance Perovskite Solar Cells

The designed hole-transporting materials (HTMs) of asymmetric and symmetric benzoselenadiazole based molecules, referred as RSe-CF, RSe-TPA, and RSe-R, were synthesized and employed for improving the charge conduction and performance of mixed-halide (Cs0.03FA0.97PbI2.9Br0.1) perovskite solar cells (PSCs). In this work, the effects of different acceptor/donor units like 3,5-bis(trifluoromethyl) benzene (CF), alkyl thiophene (R), and triphenylamine (TPA) in benzoselenadiazole were investigated and their optoelectronic, structural, thermal, and photovoltaic properties were studied. The optical and electrochemical results of RSe-CF, RSe-TPA, and RSe-R exhibited the alternation of the energy levels for efficient interfacial charge transfer with mixed-halide Cs0.03FA0.97PbI2.9Br0.1. RSe-TPA HTM-based PSCs displayed the highest power conversion efficiency (PCE) of ∼17.3%, whereas PSCs based on RSe-CF and RSe-R HTMs displayed low PCEs of ∼12.4% and ∼15.9%, respectively. The PCE with a new RSe-TPA HTM is comparable to the PCE of the state-of-the-art HTM Spiro-OMeTAD. Observation of large quenching in photoluminescence spectra of the HTM/Cs0.03FA0.97PbI2.9Br0.1 thin film supported the effective hole injection from perovskite’s valence band to HOMO of HTMs, resulting in high PCE and high photocurrent density.

Effect of regioregularity and role of heteroatom on the chiral behavior of oligo(heteroalkyl thiophene)s.

Novel optically active oligothiophenes bearing electron-donating chiral side chains have been prepared by synthetic methods suitable to achieve regioregular head-to-tail and head-to-head/tail-to-tail derivatives. In particular, the chiral (S)-(2-methyl)butyl moiety was linked at position 3 of the thiophene ring through heteroatoms, such as S or O, to evaluate its effect on the macro molecular aggregation and, consequently, on the chiroptical properties of the material in the solid state. The materials have been fully characterized and investigated by optical and chiroptical methods upon aggregation both from the solution and as cast films. Compared with the related head-to-tail and head-to-head/tail-to-tail poly(3-alkyl)thiophene derivatives, with the same optically active moiety directly linked to the ring and possessing a higher polymerization degree, the chiroptical properties of the newly synthesized oligomers were significant, or even better, and provided insight into the role of intrachain-interchain interactions between the heteroatom and the thienyl sulfur atom.

A systematic evaluation of triisopropylsilylethynyl-substituted thienyl side chain effects on series of benzo[1,2-b:4,5-b′]dithiophene based polymer donors and their photovoltaic performances

In this report three new donor copolymers based on alternate octyl 3-fluorothieno[3,4-b]thiophene-2-carboxylate as acceptor and benzo[1,2-b:4,5-b′]dithiophene (BDT) derivatives having triisopropylethynylsilane (TIPS), triisopropyl((thiophen-2-yl)ethynyl)silane (TIPS-Th) and triisopropyl((3-octylthiophen-2-yl)ethynyl)silane (TIPS-ThC8) side chains as donors, (respectively named as P1, P2 and P3) are synthesized to assess whether insertion of thiophene or alkyl thiophene units between TIPS side chains and BDT backbones can improve their properties and photovoltaic performance. Indeed, the modification of TIPS side chains on BDT backbone found to distinctly affect their opto-electrochemical properties, molecular orientations and nanoscale morphologies in resultant polymers. Among the polymers, optimized organic solar cells (OSCs) of P1:PC71BM exhibited best power conversion efficiency (PCE) of 6.55% with a very high VOC of 1.02 V, thereby outperforming P2 and P3 (PCE of 4.72% and 5.47%, respectively). The detailed characterization of optimized blends revealed that this superior device performance of P1:PC71BM blend films attributed to their compact and “face-on” molecular orientation, high hole mobility and superior nanoscale morphology, which minimized voltage loss and leading to an efficient charge transfer with low recombination losses in OCSs. In contrast, lower performances of P2 and P3 were mainly originating from their decreased solubilities caused by the insertion of TIPS-Th or TIPS-ThC8, thereby negatively affecting their molecular weights, morphology and charge carrier mobilities. Thus, these results provide a valuable guideline for designing polymers based on 2-TIPSTh substituted BDT units.

Soluble Electrochromic Polymers Incorporating Benzoselenadiazole and Electron Donor Units (Carbazole or Fluorene): Synthesis and Electronic-Optical Properties.

A series of π-conjugated polymers containing alternating benzoselenadiazole (BSe)-bi(thiophene derivative)-carbazole or benzoththiadiazole (BSe)-bi(thiophene derivative)-fluorene units were designed and synthesized. Thiophene derivatives, namely 3-hexylthiophene, 3,4-bihexyloxythiophene, and 3,4-bioctyloxythiophene, were used as the π-bridges of the polymers. The polymers were characterized in detail in terms of their thermal stabilities, cyclic voltammograms, UV-Vis absorption, spectroelectrochemistry, dynamic switching property and so forth. The alkoxy thiophene π-bridged polymers have lower onset oxidation potentials and bandgaps than that of their corresponding alkyl thiophene π-bridged polymers. The selection of the donor units between the carbazole and the fluorene units has nearly no effect on the bandgaps and colors as well as the onset oxidation potentials of the polymers. The increase in the length of the side alkyl chains on the thiophene ring caused a slight increase in the polymer bandgap, which may be caused by the space hindrance effect. The dynamic switching abilities of the polymers were obtained by the chronoabsorptometry method, and the results also suggested that the alkoxy thiophene-containing polymers (as π-bridges) have higher contrast ratios than the corresponding alkyl thiophene-containing polymers. Furthermore, the increase in the length of the side alkyl chain might have a detrimental effect on the optical contrast ratios of the polymers.

Donor Engineering for NIR-II Molecular Fluorophores with Enhanced Fluorescent Performance.

Organic fluorophores have been widely used for biological imaging in the visible and the first near-infrared windows. However, their application in the second near-infrared window (NIR-II, 1000-1700 nm) is still limited mainly due to low fluorescence quantum yields (QYs). Here, we explore molecular engineering on the donor unit to develop high performance NIR-II fluorophores. The fluorophores are constructed by a shielding unit-donor(s)-acceptor-donor(s)-shielding unit structure. Thiophene is introduced as the second donor connected to the shielding unit, which can increase the conjugation length and red-shift the fluorescence emission. Alkyl thiophene is employed as the first donor connected to the acceptor unit. The bulky and hydrophobic alkyl thiophene donor affords larger distortion of the conjugated backbone and fewer interactions with water molecules compared to other donor units studied before. The molecular fluorophore IR-FTAP with octyl thiophene as the first donor and thiophene as the second donor exhibits fluorescence emission peaked at 1048 nm with a QY of 5.3% in aqueous solutions, one of the highest for molecular NIR-II fluorophore reported so far. Superior temporal and spatial resolutions have been demonstrated with IR-FTAP fluorophore for NIR-II imaging of the blood vessels of a mouse hindlimb.

Alkylthienyl substituted asymmetric 2D BDT and DTBT-based polymer solar cells with a power conversion efficiency of 9.2%

An alkyl thiophene unit was employed for the first time as a side chain substituent on an asymmetric benzodithiophene (BDT) building block in the design of novel light-harvesting polymers.

Soft Templating of Water Aggregates Disrupts π–π Stacking in Crystalline Poly(3-hexylthiophene)

The π–π stacking robustness of the photoactive layer is key to maintaining efficiency of organic photovoltaics (OPVs). We show local disruption more than 2 A on average in the π–π stack of crystalline poly(3-hexylthiophene) (P3HT), one of the most common materials used in OPVs, through formation of a chainlike water structure with limited growth and mostly pentameric cluster ends. In contrast, a 3D aggregated water cluster with constant growth is observed in amorphous P3HT. Dynamics of water molecules that form the largest aggregates in crystalline P3HT show the effect of limited mobility, when compared to amorphous P3HT, due to dual confinement from both alkyl side groups and thiophene backbone. We term this dual confinement soft templating and quantify its effect on nature, size, and hydrogen bond participation of water aggregates in crystalline and amorphous P3HT using all-atom molecular dynamics with in-house developed potentials that were previously shown to represent the interfacial and wetting beha...

Design and synthesis of thieno[3,4‐c]pyrrole‐4,6‐dione based conjugated copolymers for organic solar cells

AbstractA new series of conjugated copolymers (PBDT‐TPD, PBDT‐Th‐TPD, PBDT‐TT‐TPD) containing donor–acceptor (D − A) structure electron‐rich benzo[1,2‐b:4,5‐b′]dithiophene (BDT) units with branched alkyl thiophene side chains and electron‐deficient 5‐(2‐octyl)‐4H‐thieno[3,4‐c]pyrrole‐4,6(5H)‐dione (TPD) units was designed and synthesized. To tune the optical and electrochemical properties of the copolymers, the conjugation length of the copolymers was extended by introducing π‐conjugated spacers such as thiophene and thieno[3,2‐b]thiophene units. It was observed that PBDT‐TPD showed broader absorption spectra in the longer wavelength region and the absorption maximum was red‐shifted compared to that of PBDT‐Th‐TPD, PBDT‐TT‐TPD. Stokes shifts were calculated to be 52 nm for PBDT‐TPD, 153 nm for PBDT‐Th‐TPD and 146 nm for PBDT‐TT‐TPD. Further, PBDT‐TPD exhibited a deeper highest occupied molecular orbital energy level of −5.53 eV as calculated by cyclic voltammetry. Bulk heterojunction solar cells fabricated using PBDT‐TPD as donor material exhibited a power conversion efficiency of 1.92%. © 2017 Society of Chemical Industry

Harnessing Structure–Property Relationshipsfor Poly(alkyl thiophene)–Fullerene Derivative Thin Filmsto Optimize Performance in Photovoltaic Devices

Nanoscale bulk heterojunction (BHJ) systems, consisting of fullerenes dispersed in conjugated polymers have been actively studied in order to produce high performance organic photovoltaics. How the BHJ morphology affects device efficiency, is currently ill‐understood. Neutron reflection together with grazing incidence X‐ray and neutron scattering and X‐ray photoelectron spectroscopy are utilized to gain understanding of the BHJ morphology in functional devices. For nine model systems, based on mixtures of three poly(3‐alkyl thiophenes, P3AT) (A = butyl, hexyl, octyl) blended with three different fullerene derivatives, the BHJ morphology through the film thickness is determined. It is shown that fullerene enrichment occurs at both the electrode interfaces after annealing. The degree of fullerene enrichment is found to strongly correlate with the short circuit current (JSC ) and to a lesser degree with the fill factor. Based on these findings, it is demonstrated that by deliberately adding a fullerene layer at the electron transport layer interface, JSC can be increased by up to 20%, resulting in an overall increase in power conversion efficiency of 5%.

About different packing states of alkyl groups in comb-like polymers with rigid backbones.

We report a comparative X-ray diffraction study on three series of comb-like polymers with rigid backbones and layered morphologies [regio-regular poly(3-alkyl thiophenes), alkoxylated polyesters, alkoxylated polyphenylenevinylenes] highlighting the importance of the volume per methylene unit VCH2 in alkyl nanodomains for the overall packing state. We demonstrate that there is a large (≈30%) variation in the VCH2 values for different polymer series and packing states but no significant change in VCH2 depending on the length of the alkyl side groups. This calls into question commonly used structural models which are based only on tilting and interdigitation of ideally stretched alkyl side groups. We argue that a linear dependence of the layer spacings with side chain length can also be explained by a constant VCH2 value and unchanged main chain packing. The potential importance of side chain packing for the occurrence of different (liquid-) crystalline modifications in various polymer series and possible interrelations between main and side chain packings are discussed.

Polythiophenes with Thiophene Side Chain Extensions: Convergent Syntheses and Investigation of Mesoscopic Order

A versatile convergent synthesis route to side chain π-extended, highly regioregular polythiophenes is presented. The implementation of β-conjugated alkyl thiophene branches in linear polythiophenes is used as synthetical tool for energy level engineering, with branched alkyl chains being introduced for solubility reasons. While the length of the branched alkyl side chains does not influence the functional properties, the aggregation behavior in solution does vary from highly aggregated to fully dissolved at room temperature. Temperature-dependent UV–vis spectroscopy highlights the differences in the aggregation behavior in solution and thin films. The aggregation behavior in solid state is further studied using DSC, temperature-dependent Raman spectroscopy and temperature-dependent XRD. Finally, controlled crystallization conditions via solvent vapor annealing are applied to allow the formation of spherulite-like structures which reveal a face-on orientation of the polymer backbone with respect to the su...

The role of steric interactions in dispersion of carbon nanotubes by poly(3-alkyl thiophenes) in organic solvents

The dispersion mechanism of carbon nanotubes (CNTs) in organic solutions of poly(3-alkyl thiophenes, P3ATs) was examined in a study that combines experimental investigation of the dispersion mechanism and molecular theory calculations of the effective intertube potential for polymer wrapped CNTs. The minimal polymer concentration required for dispersion of CNT served as a comparative measure of the efficiency of P3AT derivatives that differ in the length of the alkyl side chains or the regiochemistry of the monomers in three solvents: 1,2 and 1,3 dichlorobenzene and chloroform. While previous studies focused on the adsorption mechanism of P3ATs onto SWNT, we find that the dispersing efficiency depends not only on the stacking of the polymer backbone onto the CNT (“wrapping”), but also on the steric repulsion among the side chains of adsorbed P3ATs. In accordance with the experiments, our calculations indicate that high surface density of polymers with longer side chains and large tube diameter promote the formation of stable dispersions of relatively high loadings of CNTs, at low polymer:CNT ratios.

Carbazole-based sensitizers for potential application to dye sensitized solar cells

Two push-pull molecules employing carbazole and alkyl thiophene (CAR-THIOHX) or carbazole and triphenylamine (CAR-TPA) as donor moieties, with the cyanoacrylic group as the acceptor, have been designed and synthesized by simple organic transformations. Photophysical and electrochemical studies revealed the potential of these two systems in dye sensitized solar cells (DSSC). Under standard irradiation conditions, CAR-TPA and CAR-THIOHX exhibited 2.12 and 1.83% of overall power conversion efficiencies respectively. The moderate photovoltaic efficiency of the sensitizers has been attributed to the poor light absorption of the sensitizers in the visible region. Density functional theory (DFT) calculations have shown a strong intramolecular charge transfer character, with the HOMOs of both the sensitizers exclusively localized on the corresponding donor moieties and LUMOs on the cyanoacrylic acid acceptor. On the other hand, the calculated high dihedral angle between the carbazole donor and the phenyl bridge for these sensitizers impedes the conjugation along the dyes backbone, and thus leads to less extended and intense absorption spectra in the visible region. Two push-pull carbazole based molecules, CAR-THIOHX and CAR-TPA, have been designed and synthesized by simple organic transformations. Photophysical and electrochemical studies revealed the potential of these two molecules in dye sensitized solar cells (DSSC). Under standard irradiation conditions, CAR-TPA and CAR-THIOHX exhibited 2.12 and 1.83% of overall power conversion efficiencies, respectively.

Optically active, regioregular, head-to-head/tail-to-tail poly(3-alkyl)thiophene by inherently regiospecific oxidative synthesis from 3,3′-dialkyl 2,2′-bithiophene monomer

A fully regioregular poly(3-alkylthiophene) displaying only head-to-head/tail-to-tail connections between thiophene rings has been prepared by oxidative chemical or electrochemical polymerization starting from a symmetrical bithiophene monomer bearing at the β positions the optically active S-(+)-2-methylbutyl group. The polymeric product has been fully characterized as far as its spectroscopic, solvatochromic, chiroptical, thermal, electrochemical and morphological properties are concerned. In particular, the solvatochromic, chiroptical and thermal properties have been compared to those of the related, well known, head-to-tail regioregular polymeric derivative possessing the same side-chain substituent in order to elucidate the structural features characterizing the head-to-head regioregular derivative.

Confined relaxation dynamics in long range ordered polyesters with comb-like architecture

The cooperative relaxation dynamics of methylene units in self-assembled amorphous alkyl nanodomains with typical dimensions in the range 5–20 Å is studied in a series of poly(1,4-phenylene-2,5-n-dialkyloxy terephthalate)s (PPAOTs) with C = 6–12 alkyl carbons per side chain. These comb-like polymers are long range ordered on the nanoscale since domains where main chains are stacked in a crystal-like manner alternate with alkyl nanodomains formed by aggregated side chains. Dynamic mechanical data for the investigated PPAOTs show polyethylene-like glass transitions αPE which are similar to those for many other polymer series with comb-like architecture containing long alkyl side groups. Hence, self-assembled PPAOTs are excellent model systems for studies focusing on a detailed understanding of the influence of (i) alkyl nanodomain size, (ii) average volume per CH2 unit and (iii) number of alkyl groups per interfacial area on the cooperative dynamics of methylene units seen as αPE process. Structural parameters as obtained from X-ray diffraction experiments allow to deduce quantitative information about these influencing factors. The results are compared with those for regio-regular poly(3-alkyl thiophenes) with similar molecular architecture. The comparison shows that important features of the αPE process within amorphous alkyl nanodomains are main chain independent even in case of long-range ordered polymers with quite different main chain packing. It is concluded that the alkyl nanodomain size is the most important factor determining the αPE dynamics of the methylene units. Main chain dependent aspects like average volume per CH2 unit and interfacial constraints do only weakly influence the relaxation behavior within the alkyl nanodomains.

Symmetrically Disubstituted Bithiophene Derivatives of 1,3,4-Oxadiazole, 1,3,4-Thiadiazole, and 1,2,4-Triazole – Spectroscopic, Electrochemical, and Spectroelectrochemical Properties

Electrochemical and spectroelectrochemical properties of a series of new penta-ring donor–acceptor compounds, comprising 1,3,4-oxadiazole, 1,3,4-thiadiazole, and 1,2,4-triazole central ring, symmetrically connected to substituted bithiophenes, were investigated. Aromaticity and electrophilic–nucleophilic traits of the aza-heterocyclic units, fostering inductive and resonance effects that translate to conjugation enhancement and electron (de)localization, were found a major factor determining the key electron properties of ionization potential (IP) and electron affinity (EA) of these molecules. Replacing the alkyl thiophene substituent for an alkoxy one afforded certain control over the two parameters as well. All studied compounds were found to undergo electrochemical polymerization giving p- and n-dopable products, featuring good electrochemical reversibility of their oxidative doping process, as demonstrated by cyclic voltammetry and UV–vis–NIR, EPR spectroelectrochemistry. While electropolymerization o...

Improved photovoltaic performance of two-dimensional low band-gap conjugated polymers with thieno[3,2-b]thiophene and diketopyrrolopyrrole units by altering pendent position of conjugated side chain

Two-dimensional low band-gap copolymers of P1 and P2 with a framework of (2,5-di(thiophen-2-yl)thieno[3,2-b]thiophene)-alt-(2,5-bis(2-ethylhexyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione) (DTTT-alt-DTPP) were synthesized, in which two 2,3-dioctylthiophene-5-yl groups were pended into the 3-positions of two thiophenyl rings close to the thieno[3,2-b]thiophene (TT) unit for P1 and the 3, 6-positions of the TT unit for P2, respectively. The influence of pending positions on optophysical and photovoltaic properties were studied. Similar broad absorption spectra from 350 to 950 nm were observed with a low band-gap of 1.25 eV. However, significantly different photovoltaic properties were obtained in the bulk heterojunction polymer solar cells with a device structure of ITO/PEDOT:PSS/active layer/LiF/Al. The P1-based devices showed a power conversion efficiency (PCE) of 0.79%, but the P2-based devices displayed a notably increasing PCE up to 2.12% under an AM 1.5G irradiation with an intensity of 100 mW cm−2. Our results indicate that altering pendent position of alkyl thiophene is effective way to improve the photovoltaic properties for the two-dimensional copolymers.

Effects of donor unit and π‐bridge on photovoltaic properties of D–A copolymers based on benzo[1,2‐b:4,5‐c']‐dithiophene‐4,8‐dione acceptor unit

ABSTRACTA series of donor‐π‐acceptor (D‐π‐A) conjugated copolymers (PBDT‐AT, PDTS‐AT, PBDT‐TT, and PDTS‐TT), based on benzo[1,2‐b:4,5‐c']dithiophene‐4,8‐dione (BDD) acceptor unit with benzodithiophene (BDT) or dithienosilole (DTS) as donor unit, alkylthiophene (AT) or thieno[3,2‐b]thiophene (TT) as conjugated π‐bridge, were designed and synthesized for application as donor materials in polymer solar cells (PSCs). Effects of the donor unit and π‐bridge on the optical and electrochemical properties, hole mobilities, and photovoltaic performance of the D‐π‐A copolymers were investigated. PSCs with the polymers as donor and PC70BM as acceptor exhibit an initial power conversion efficiency (PCE) of 5.46% for PBDT‐AT, 2.62% for PDTS‐AT, 0.82% for PBDT‐TT, and 2.38% for PDTS‐TT. After methanol treatment, the PCE was increased up to 5.91%, 3.06%, 1.45%, and 2.45% for PBDT‐AT, PDTS‐AT, PBDT‐TT, and PDTS‐TT, respectively, with significantly increased FF. The effects of methanol treatment on the photovoltaic performance of the PSCs can be ascribed to the increased and balanced carrier transport and the formation of better nanoscaled interpenetrating network in the active layer. The results indicate that both donor unit and π‐bridge are crucial in designing a D‐π‐A copolymer for high‐performance photovoltaic materials. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1929–1940

A versatile approach for creating hybrid semiconducting polymer–fullerene architectures for organic electronics

A novel methodology, through which fullerenes are effectively introduced directly onto semiconducting species, is presented herein. Electron accepting perfluorophenyl-quinolines either as small molecules, as homopolymers, or as random copolymers with regioregular poly(3-alkyl thiophene), have been synthesized and further employed for the preparation of hybrid materials with C60 or PCBM. More specifically, via this route one of the fluorine atoms of the perfluorophenyl ring is transformed into an azide that undergoes [3+2]-cycloaddition onto the fullerene's surface, producing 1,6-azo bridged carbon nanostructure–organic semiconducting hybrids.