Synergistic electrodeposition of bilayer films and analysis by Raman spectroscopy.

A novel methodology towards fabrication of multilayer organic devices, employing electrochemical polymer growth to form PEDOT and PEDTT layers, is successfully demonstrated. Moreover, careful control of the electrochemical conditions allows the degree of doping to be effectively altered for one of the polymer layers. Raman spectroscopy confirmed the formation and doped states of the PEDOT/PEDTT bilayer. The electrochemical deposition of a bilayer containing a de-doped PEDTT layer on top of doped PEDOT is analogous to a solution-processed organic semiconductor layer deposited on top of a PEDOT:PSS layer without the acidic PSS polymer. However, the poor solubility of electrochemically deposited PEDTT (or other electropolymerised potential candidates) raises the possibility of depositing a subsequent layer via solution-processing.

Polythiophene and oligothiophene systems modified by TTF electroactive units for organic electronics.

The aim of this review is to give an update on current progress in the synthesis, properties and applications of thiophene-based conjugated systems bearing tetrathiafulvalene (TTF) units. We focus mostly on the synthesis of poly- and oligothiophenes with TTF moieties fused to the thiophene units of the conjugated backbone either directly or via a dithiin ring. The electrochemical behaviour of these materials and structure-property relationships are discussed. The study is directed towards the development of a new type of organic semiconductors based on these hybrid materials for application in organic field effect transistors and solar cells.

Solution processable diketopyrrolopyrrole (DPP) cored small molecules with BODIPY end groups as novel donors for organic solar cells.

Two novel triads based on a diketopyrrolopyrrole (DPP) central core and two 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) units attached by thiophene rings have been synthesised having high molar extinction coefficients. These triads were characterised and used as donor materials in small molecule, solution processable organic solar cells. Both triads were blended with PC71BM as an acceptor in different ratios by wt % and their photovoltaic properties were studied. For both the triads a modest photovoltaic performance was observed, having an efficiency of 0.65%. Moreover, in order to understand the ground and excited state properties and vertical absorption profile of DPP and BODIPY units within the triads, theoretical DFT and TDDFT calculations were performed.

Synthesis and properties of novel star-shaped oligofluorene conjugated systems with BODIPY cores.

Star-shaped conjugated systems with varying oligofluorene arm length and substitution patterns of the central BODIPY core have been synthesised, leading to two families of compounds, T-B1-T-B4 and Y-B1-Y-B4, with T- and Y-shaped motifs, respectively. Thermal stability, cyclic voltammetry, absorption and photoluminescence spectroscopy of each member of these two families were studied in order to determine their suitability as emissive materials in photonic applications.

Poly([1,4]Dithiino[2,3-c]Furan): the synthesis, electrochemistry, and optoelectronic properties of a furan-containing polymer.

The chemical synthesis of a novel polyfuran, poly(2,3-bis(hexylthio)-[1,4]dithiino[2,3-c]furan) (PBDF), substituted at the 2,3-positions with an S-alkylated dithiin unit, is reported. The new polymer has been characterized in terms of its electronic absorption, electrochemical, and thermal properties. Employment of the dithiin moiety provides intrinsic additional electroactivity, as well as a functional handle for substitution with alkyl groups, enhancing the processability of the polymer. The new polymer is compared with the closely related and well-established literature compounds PEDOT and PEDTT as well-studied, highly chalcogenated polythiophenes.

Incorporation of perfluorohexyl-functionalised thiophenes into oligofluorene-truxenes: synthesis and physical properties.

Oligofluorene-functionalised truxenes containing perfluorohexylthiophene units at the terminal positions on the arms were synthesised, and their optical and electrochemical properties were investigated to determine the effect that the perfluorohexylthiophene unit has on the HOMO and LUMO properties of the oligomers. By synthesising a molecule with longer oligofluorene arms the effects of the perfluorohexylthiophene unit on larger oligomers was explored. The effect of steric hindrance from the perfluorohexyl chain was also evaluated by altering the position of the chain on the thiophene moiety.

A pyridine-capped quaterthiophene as an alternative to PEDOT:PSS, processable from organic solvents and without acidity, for more stable electronic devices.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a material that has become ubiquitous in the field of organic electronics. It is most commonly used as a hole transport layer (HTL) in optoelectronic devices and can be purchased commercially in various formulations with different properties. Whilst it is a most convenient material to work with, there are stability issues associated with PEDOT:PSS that are detrimental to device stability and these are due to the acidic nature of the PSS component. In this paper, we present a molecular, non-acidic alternative to PEDOT:PSS. The parent structure is composed of a quater(3,4-ethylenedioxythiophene) unit capped either side of the short chain with two pyridine units. This compound, termed (BEDOTPy)2, can be prepared chemically and electrochemically to give doped materials with a choice of counteranions. Further functionalisation via quaternisation at the nitrogen atoms allows for modification of solubility and film-forming properties. The conductivity of the doped samples can reach up to 3.75 S cm-1. The materials are non-acidic and are therefore attractive alternatives to PEDOT:PSS for device applications. We demonstrate an OLED device using the compound (BEDOTPy-EtOH-I)2PF6 as an HTL, and compare the device performance to one made with PEDOT:PSS. Due to the non-acidic nature of the molecular material, the corresponding OLED device does not show a drop in luminance over time, whereas a loss of performance is observed for the device containing PEDOT:PSS over a short period. These results are presented to introduce the parent compound (BEDOTPy)2 as an attractive alternative to PEDOT:PSS, which can be easily modified chemically to provide a plethora of potential compounds with tunable properties.

Sexithiophenes as efficient luminescence quenchers of quantum dots.

Sexithiophenes 1a and 1b, in which a 4-(dimethylamino)phenyl unit is incorporated as an end-capping group, were synthesised and characterised by cyclic voltammetry, absorption spectroscopy and UV-vis spectroelectrochemistry. Additionally, their ability to function as effective luminescence quenchers for quantum dot emission was studied by photoluminescence spectroscopy and compared with the performance of alkyl end-capped sexithiophenes 2a and 2b.

Highly nonlinear transport across single-molecule junctions via destructive quantum interference.

To rival the performance of modern integrated circuits, single-molecule devices must be designed to exhibit extremely nonlinear current-voltage (I-V) characteristics1-4. A common approach is to design molecular backbones where destructive quantum interference (QI) between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) produces a nonlinear energy-dependent tunnelling probability near the electrode Fermi energy (EF)5-8. However, tuning such systems is not straightforward, as aligning the frontier orbitals to EF is hard to control9. Here, we instead create a molecular system where constructive QI between the HOMO and LUMO is suppressed and destructive QI between the HOMO and strongly coupled occupied orbitals of opposite phase is enhanced. We use a series of fluorene oligomers containing a central benzothiadiazole10 unit to demonstrate that this strategy can be used to create highly nonlinear single-molecule circuits. Notably, we are able to reproducibly modulate the conductance of a 6-nm molecule by a factor of more than 104.

Reductions of challenging organic substrates by a nickel complex of a noninnocent crown carbene ligand.

The first crown-tetracarbene complex of Ni(II) has been prepared, and its crystal structure determined. The complex can be reduced by Na/Hg, with an uptake of two electrons. The reduced complex reductively cleaves arenesulfonamides, including those derived from secondary aliphatic amines, and effects Birch reduction of anthracenes as well as reductive cleavage of stilbene oxides. Computational studies show that the orbital that receives electrons upon reduction of the complex 2 is predominantly based on the crown carbene ligand and also that the HOMO of the parent complex 2 is based on the ligand.

One-carbon extrusion from a tetraazafulvalene. Isolation of aldehydes and a study of their origin.

Reaction of imidazolylidene-derived enetetramine 2 with aliphatic iodides and bromides (and with aryl iodides bearing alkene-containing side-chains in the ortho-position) leads to formation of aliphatic aldehydes through an unprecedented extrusion of a one-carbon unit from the enetetramine. An intermediate 2-alkylimidazoline 24 is proposed, where the alkyl group derives from the substrate; this imidazoline undergoes further reaction in situ to afford the observed aldehydes on acidic workup. Modified substrates were designed and prepared to probe the chemistry of the alkylimidazoline adducts and provided extensive information on the chemistry of the adducts.

Metal-free reductive cleavage of C-O sigma-bonds in acyloin derivatives by an organic neutral super-electron-donor.

Neutral organic electron-donor 7, formally a pyridinylidene carbene dimer, effects reductive cleavage of C-O sigma-bonds in acyloin derivatives Ar(CO)CRR'OX (X = OAc, OPiv, OBz, OMs) and this represents the first cleavage of C-O sigma-bonds by a neutral organic electron-donor. The methodology is applicable to a large array of substrates and the reduced counterparts were isolated in good to excellent yields. For certain substrates, donor 7 behaves as a base, effecting condensation reactions with some acetate ester derivatives of acyloins, leading to butenolides. The variation in reactivity among the different substrates was rationalized.

Scale-up Chemical Synthesis of Thermally-activated Delayed Fluorescence Emitters Based on the Dibenzothiophene-S,S-Dioxide Core.

We report a procedure to linearly scale-up the synthesis of 2,8-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)dibenzothiophene-S,S-dioxide (compound 4) and 2,8-bis(10H-phenothiazin-10-yl)dibenzothiophene-S,S-dioxide (compound 5) using Buchwald-Hartwig cross-coupling reaction conditions. In addition, we demonstrate a scaled-up synthesis of all non-commercially available starting materials that are required for the amination cross-coupling reaction. In the present article, we provide the detailed synthetic procedures for all of the described compounds, alongside their spectral characterization. This work shows the possibility to produce organic molecules for optoelectronic applications on a large scale, which facilitates their implementation into real world devices.

An Ambipolar BODIPY Derivative for a White Exciplex OLED and Cholesteric Liquid Crystal Laser toward Multifunctional Devices.

A new interface engineering method is demonstrated for the preparation of an efficient white organic light-emitting diode (WOLED) by embedding an ultrathin layer of the novel ambipolar red emissive compound 4,4-difluoro-2,6-di(4-hexylthiopen-2-yl)-1,3,5,7,8-pentamethyl-4-bora-3a,4a-diaza-s-indacene (bThBODIPY) in the exciplex formation region. The compound shows a hole and electron mobility of 3.3 × 10-4 and 2 × 10-4 cm2 V-1 s-1, respectively, at electric fields higher than 5.3 × 105 V cm-1. The resulting WOLED exhibited a maximum luminance of 6579 cd m-2 with CIE 1931 color coordinates (0.39; 0.35). The bThBODIPY dye is also demonstrated to be an effective laser dye for a cholesteric liquid crystal (ChLC) laser. New construction of the ChLC laser, by which a flat capillary with an optically isotropic dye solution is sandwiched between two dye-free ChLC cells, provides photonic lasing at a wavelength well matched with that of a dye-doped planar ChLC cell.

An organic down-converting material for white-light emission from hybrid LEDs.

A novel BODIPY-containing organic small molecule is synthesized and employed as a down-converting layer on a commercial blue light-emitting diode (LED). The resulting hybrid device demonstrates white-light emission under low-current operation, with color coordinates of (0.34, 0.31) and an efficacy of 13.6 lm/W; four times greater than the parent blue LED.