Oligothiophene Derivatives Research Articles

Oligothiophene Derivatives Functionalized with a Diketopyrrolopyrrolo Core for Solution-Processed Field Effect Transistors: Effect of Alkyl Substituents and Thermal Annealing

Two new oligothiophene derivatives bearing a diketopyrrolopyrrole core, 2,5-di-n-hexyl-3,6-bis(5′′-n-hexyl[2,2′;5′,2′′]terthiophen-5-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (DHT6DPPC6) and 2,5-di-n-dodecyl-3,6-bis(5′′-n-hexyl[2,2′;5′,2′′]terthiophen-5-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (DHT6DPPC12), and their use in solution-processed organic field effect transistors are reported. Depending on the type of alkyl substituent and film annealing temperature, the crystal grain sizes and interlayer spacing vary as observed using atomic force microscopy and X-ray diffractometry, respectively. These changes in film morphology and interlayer spacing lead to an order of magnitude difference in the field effect mobilities. The field effect mobilities for annealed DHT6DPPC6 and DHT6DPPC12 films are 0.02 and 0.01 cm2/V s, respectively.

Design, Synthesis, and Self-assembly of Oligothiophene Derivatives with a Diketopyrrolopyrrole Core

Oligothiophenes containing diketopyrrolopyrrole (DPP) cores were synthesized, and their electrochemistry, photophysics, and film morphology were studied. Density functional theory calculations indicate that the highest occupied molecular orbital and the lowest unoccupied molecular orbital can be tuned by changing the number of thiophene units. The compounds synthesized in this study had electrochemical gaps ranging from 1.80 to 2.25 V and intense absorption bands in the UV, assigned to the thiophene units, as well as bands in the visible part of the spectrum, attributed to charge-transfer transitions between the electron-rich thiophene moieties and the electron-withdrawing DPP core. All of the compounds were found to be luminescent in solution with emission wavelengths ranging from 562 to 682 nm. Atomic force microscopy studies show that the length and type of alkyl substitution on the DPP core affect the film morphology, and hence, the solid state photophysical and electronic properties. Long and straight alkyl chains lead to rod-like or needle-like structures, whereas compounds with branched alkyl chains do not show ordering in the solid state. The self-assembling process can also be manipulated by changing the number of thiophene units. Nanoscale fibrous structures were obtained when either two or four thiophene units were added to the initial bis-thiophenyl-DPP unit.

Electrochromic Properties Based on Oligothiophene Derivatives

AbstractIn order to develop novel electrochromic materials, 5,5′′‐dicyano‐2,2′:5′,2′′‐terthiophene (DCN3T), 5,5′′′‐dicyano‐2,2′:5′,2′′:5′′,2′′′‐tetrathiophene (DCN4T), 5,5′′′‐dimethoxy‐2,2′:5′,2′′:5′′,2′′′‐tetrathiophene (DMO4T) and 4,4′′‐bicarboxyl‐5,5′′‐bipropyl‐2,2′:5′,2′′‐terthiophene (BP3T‐DCOOH) were synthesized, and their electrochromic properties were studied. It was found that DCN3T, DCN4T, DMO4T and BP3T‐DCOOH as solid films showed reversible, clear color changes on electrochemical doping and dedoping.

Isomeric Discriminating and Indiscriminating Assembly of Adsorbed Oligothiophenes on Ag(110)

Selective discriminating and indiscriminating assembly of isomeric oligothiophene derivatives is performed on a Ag(110) surface. The self-assembled structures are directly analyzed by using scanning tunneling microscopy. We demonstrate that the phase separation and phase mixing of s-cis- and s-trans-oligothiophenes can be controlled by shape-complementary intermolecular interactions associated with the overall molecular shapes. The overall shapes of the s-cis- and s-trans-oligothiophenes are tuned by the length of alkyl side chains.

A Low Band Gap, Solution Processable Oligothiophene with a Diketopyrrolopyrrole Core for Use in Organic Solar Cells

We synthesized a low band gap, solution processable oligothiophene derivative functionalized with a diketopyrrolopyrrole core, which is a highly absorbing chromophoric group. This design leads to optical absorption that extends to 720 nm in solution and to 820 nm in the film. Cyclic voltammetry shows quasireversible oxidation and reduction processes. Bulk heterojunction solar cells using [6,6]-phenyl C61-butyric acid methyl ester (PCBM) as the electron acceptor were fabricated. The power conversion efficiencies (PCEs) depend on the donor−acceptor ratio. A 70:30 donor/acceptor by weight mixture provided a PCE of 2.3% under simulated AM 1.5 solar irradiation of 100 mW/cm 2. To date, this is the highest efficiency reported for small molecule-based solution processed bulk heterojunction solar cells.

Self-Sorting Organogels with p−n Heterojunction Points

We report on a self-sorting supramolecular fiber formation of photo- and electro-active molecules (p-type oligothiophene and n-type perylene derivatives) toward the development of a photoelectronic conversion system operated by visible light irradiation.

Flexible organic photovoltaic devices based on oligothiophene derivatives

For the purpose of developing flexible organic photovoltaic devices, we have fabricated two flexible devices using 5-formyl-2,2′:5′,2″:5″,2‴-quaterthiophene (4T-CHO), 5-formyl-2,2′:5′, 2″:5″,2‴:5‴,2⁗-quinquethiophene (5T-CHO) and 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA). The PET-ITO/4T-CHO/PTCDA/Al device has an open circuit voltage ( V oc) of 1.56 V, photoelectric conversion efficiency of 0.77%. The PET-ITO/5T-CHO/PTCDA/Al device has a V oc of 1.70 V, photoelectric conversion efficiency of 0.84%. The two flexible devices have high V oc (1.56 and 1.70 V). It is possible that intermolecular hydrogen bonding between –CHO group of nT-CHO and carboxylic dianhydride of PTCDA contributes to enhancing the efficiency by promoting interfacial electron transfer and eliminating the subconducting band trap sites.

Organic Semiconductors with Helical Structure Based on Oligothiophene derivatives Exhibiting Chiral Nematic Phase

We have synthesized 2-[5-(4-[(S)-2-methylbutoxy]phenyl)-3-methyl]-2″′-propyl-2:5′-2′:5″-2″:5″′-quaterthiophene ( 10 ), a liquid crystalline semiconductor that exhibits a chiral nematic phase, and used the time-of-flight technique to determine its carrier mobility behavior. In the chiral nematic phase, the positive carrier mobility was 2 × 10−4 cm2/Vs at 120°C and the negative carrier mobility was 1 × 10−4 cm2/Vs, both of which we attribute to electronic processes. For the negative carrier, in addition to the fast electronic process, we also observed a slow carrier transport, having mobility on the order of 10−5 cm2/Vs, which we attribute to ionic conduction. Chiral dimers containing binaphthyl group exhibited stable glassy cholesteric phase and cholesteric thin films with selective reflection band in visible light area could be fabricated. They emitted circularly polarized light with dichroic parameter of 1.3 when UV light was illuminated.

Complex Liquid‐Crystalline Superstructure of a π‐Conjugated Oligothiophene

A good connection: A polyphilic oligothiophene derivative (see formula) forms a complex liquid-crystalline phase, in which the π-conjugated rods are organized in a honeycomb-like network of square cylinders (see picture). This arrangement opens new possibilities for the directed organization of π-conjugated organic materials into complex superstructures and patterns for the design of functional devices by means of liquid-crystal self-assembly.

Sentitized near-infrared emission in novel neodymium complexes bearing oligothiophene derivatives as antennae

A series of neodymium complexes based on (α-oligothiophen-2-yl)(2-hydroxy-3-methoxyphenyl)methanone moiety was prepared and studied by FTIR, NMR, optical spectroscopies. As a function of the thiophene ring number in the ligand, a variation of both stoichiometry and optical properties of the complex are observed. The solid-state ligand structure indicates a close packing and a stressed situation in enolate residues, i.e. non-coplanarity between thiophene and phenyl moieties. An un-precedent stoichiometry of complexes was observed, namely two metal and five ligands, according to both the synthesis conditions and the encumbrance of ligand with respect to ionic radius of Nd 3+. This fact is attributed to the contribution to the coordination of the methoxy group. Luminescence and lifetime determination are discussed in the light of the above factors.

Organic solar cells on indium tin oxide and aluminum doped zinc oxide anodes

The authors compare organic solar cells using two different transparent conductive oxides as anode: indium tin oxide (ITO) and three kinds of aluminum doped zinc oxide (ZAO). These anodes with different work functions are used for small molecule photovoltaic devices based on an oligothiophene derivative as donor and fullerene C60 as acceptor molecule. It turns out that cells on ITO and ZAO have virtually identical properties. In particular, the authors demonstrate that the work function of the anode does not influence the Voc of the photovoltaic device due to the use of doped transport layers.

Structure of adsorption layers of oligothiophene derivatives: Effect of substituents

The results of computer simulation of adsorption layers composed of α-tetrathiophene derivatives via the molecular dynamics method are described. The structural organization of systems and the conformational behavior of molecules have been studied as a function of temperature and length of alkyl chains linked to β-carbon atoms of end thiophene rings.

Probing the Anisotropic Field‐Effect Mobility of Solution‐Deposited Dicyclohexyl‐α‐quaterthiophene Single Crystals

AbstractMeasuring the anisotropy of the field‐effect mobility provides insight into the correlation between molecular packing and charge transport in organic semiconductor materials. Single‐crystal field‐effect transistors are ideal tools to study intrinsic charge transport because of their high crystalline order and chemical purity. The anisotropy of the field effect mobility in organic single crystals has previously been studied by lamination of macroscopically large single crystals onto device substrates. Here, a technique is presented that allows probing of the mobility anisotropy even though only small crystals are available. Crystals of a soluble oligothiophene derivative are grown in bromobenzene and drop‐cast onto substrates containing arrays of bottom‐contact gold electrodes. Mobility anisotropy curves are recorded by measuring numerous single crystal transistor devices. Surprisingly, two mobility maxima occur at azimuths corresponding to both axes of the rectangular cyclohexyl‐substituted quaterthiophene (CH4T) in‐plane unit cell, in contrast to the expected tensorial behavior of the field effect mobility.

Organic photovoltaic devices with high open-circuit voltage based on oligothiophene derivatives

For the purpose of developing organic photovoltaic devices with good performance characteristics, we have fabricated two devices using 4T-CHO, 5T-CHO and PTCDA. The ITO/4T-CHO/PTCDA/Al device has a V oc of 2.45 V and photoelectric conversion efficiency of 2.76%. The ITO/5T-CHO/PTCDA/Al device has a V oc of 2.1 3V and photoelectric conversion efficiency of 2.90%. The two devices have higher V oc (2.45 and 2.13 V). It is possible that intermolecular hydrogen bonding between CHO group of nT-CHO and carboxylic dianhydride of PTCDA contribute to enhance the efficiency by promoting interfacial electron transfer and eliminating the subconducting band trap sites.

Synthesis, Characterization, and Properties of Homopolymers Functionalized with Oligothiophene Derivatives in the Side Chain

Two novel polynorbornenes 11 and 12 functionalized with electronically active conjugated oligomer units in the side chain were synthesized by the ring-opening metathesis polymerization (ROMP) method. Both polymers showed good optical characteristics, thermal stability, film-forming properties, and interesting electrochemical properties. The photophysical and redox behaviors of 11 and 12 are markedly different due to variation in the structure of the pendant oligomers. Polymer 11 with phenyl end-capped oligothiophene co-oligomer in the side chain showed much higher stability toward electrochemical oxidation than 12 with a sexithiophene in the side chain. This was demonstrated by in-situ study of the changes in absorption spectra of the polymer films while varying the potential in electrochemical experiments. During the p-doping process, polymer 11 exhibited highly reversible changes in its absorption peaks when monitored at 430 and 650 nm, and the p-doping/dedoping processes can be repeated many cycles. In sharp contrast, polymer 12 was shown to be electrochemically unstable under the same conditions. Single-layer photovoltaic cells have been fabricated with 11 or 12 as the active organic layer, and their relative performances were compared. These single-layer devices showed relatively large open-circuit voltage and moderate short-circuit current. In addition, the solar cell fabricated from 11 showed better device stability under ambient conditions than that from 12, which can be attributed to the higher stability of phenyl end-capped oligothiophene co-oligomer compared to that of the sexithiophene.

Effect of Pretransitional Organization in Chiral Nematic of Oligothiophene Derivatives on Their Carrier Transport Characteristics

We have synthesized three phenylquaterthiophene derivatives (liquid-crystalline semiconductors that exhibit a chiral nematic phase) and investigated their carrier transport characteristics in the chiral nematic phases with the time-of-flight technique. In contrast to the ionic nature of negative carrier transport, positive carrier transport in the chiral nematic phases of these compounds should be attributed to electronic charge carrier transport. The temperature dependence of the positive carriers in the chiral nematic phases of these compounds were strongly affected by a pretransitional smectic order formation.

High open circuit voltage organic photovoltaic cells based on oligothiophene derivatives

For the purpose of developing organic photovoltaic devices with good performance characteristics, The authors have fabricated two cells using 5-vinyl-2,2′:5′,2″:5″,2‴-quarterthiophene (V4T), 5-vinyl-2′:5′,2″:5″,2‴:5‴,2″″-quinquethiophene (V5T) and 3,4,9,10-perylenetertracarboxylic dianhydride (PTCDA). The indium tin oxide (ITO)/V4T/PTCDA/Al cell has an open circuit voltage (Voc) of 2.07V and a photoelectric conversion efficiency of 2.32%. The ITO/V5T/PTCDA/Al cell has an Voc of 1.87V and a photoelectric conversion efficiency of 2.67%. The two cells have higher Voc (1.87–2.07V). It is possible that intermolecular hydrogen bonding between –CHCH2 group of VnT with carboxylic dianhydride of PTCDA contributes to the enhancement by promoting forward interfacial electron transfer and eliminating the subconducting band trap sites.

Electronic Carrier Transport in Liquid Crystalline Semiconductors – Increase in Carrier Mobility and Extension of Mesomorphic Temperature Range

Liquid crystalline semiconductors have been recognized as one of promising materials potential for opto-electronics applications. However increase in carrier mobility as well as extension of mesomorphic temperature range is indispensable for practical applications, such as electroluminescence and thin film transistors. In this report, carrier transport in highly ordered smectic phases of oligothiophene derivatives is reported.

Efficient Vacuum‐Deposited Organic Solar Cells Based on a New Low‐Bandgap Oligothiophene and Fullerene C60

Organic solar cells based on a new oligothiophene derivative (see figure) and fullerene C60 exhibit power efficiencies of up to 3.4 %. α,α′-Bis(2,2-dicyanovinyl)-quinquethiophene (DCV5T) features a reduced optical gap with high absorption coefficients between 450 and 650 nm. Dicyanovinyl substituents on the oligothiophene rings lower the bandgap and increase the ionization energy of these oligomers, enabling the formation of photoactive heterojunctions with C60 and yielding open-circuit photovoltages as high as 1 V.

Photophysical and Electrochemical Properties of a Family of Oligothiophene Derivatives in Solution

AbstractThe photophysical and electrochemical properties of a family of oligothiophene derivatives in solution were studied. It was found that the cyano and the vinyl group could increase fluorescence yield in solution, while the formyl and carboxyl group could decrease energy gap. With increasing the chain length of thiophene ring, the oxidation potential could be decreased.