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4-(9'-Hexylcarbazol-3'-yl)benzaldehyde (Cz-Ph-CHO: 4 ) and 4-(9'-hexylcarbazol-3'- yl)benzylidenemalononitrile (Cz-Ph-CN: 5 ) were synthesised with the structure of D-pi-A,where carbazole, phenylene and formyl/dicyanovinyl groups act as electron donor (D), pi-spacer (pi) and electron acceptor (A) units, respectively. The thermal, electrochemical, optical and intramolecular charge transfer (ICT) properties of compounds 4 and 5 were investigated. Compounds 4 and 5 , in particular their ICT behaviour, were also compared with the closely related structure, 2-(9'-hexylcarbazol-3'-yl)-5-pyridinecarbaldehyde (Cz-Py-CHO: 7 ). For the purpose of tuning chemical structure to obtain targeted properties, electrochemical data and absorption and emission measurements suggest that the dicyanovinyl unit in compound 5 is a better acceptor than formyl in compound 4, and that pyridine in compound 7 is a better pi-spacer than benzene in compound 4 , in exerting ICT characteristics such as fluorosolvatochromism and Stokes shifts. (C) 2021 Elsevier B.V. All rights reserved. Scientific and Technological Research Council of Turkey (TUBITAK)Turkiye Bilimsel ve Teknolojik Arastirma Kurumu (TUBITAK); University of Glasgow; EPSRC ECR Capital Award SchemeUK Research & Innovation (UKRI)Engineering & Physical Sciences Research Council (EPSRC) [EP/S017984/1] Dr. Ahmet Battal thanks the Scientific and Technological Research Council of Turkey (TUBITAK) for 2219-International Postdoctoral Research Fellowship Programme for Turkish Citizens. Dr William Peveler acknowledges the University of Glasgow for an LKAS Scholarship and the EPSRC ECR Capital Award Scheme (EP/S017984/1) for the Duetta instrument.

To rival the performance of modern integrated circuits, single-molecule devices must be designed to exhibit extremely nonlinear current–voltage (I–V) characteristics1,2,3,4. 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)5,6,7,8. 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.

Tavasli, Mustafa/0000-0002-9466-1111; BATTAL, AHMET/0000-0003-0208-1564; Cameron, Joseph/0000-0001-8622-8353 Two novel heteroleptic iridium(III) acetylacetonate (acac) complexes K3a and K3b were synthesised from cyclometallating ligands of 2-(4'-formylphenyl)quinoline lla and 2-(5'-formylphenyl)quinoline 11b. Complexes K3a and K3b were fully characterised by NMR spectroscopy, mass spectrometry and FT-IR. Differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) indicate that both complexes were amorphous solids, stable up to 303 degrees C and 313 degrees C, respectively. Complexes K3a and K3b showed strong, high-energy absorption bands (

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS, has been widely used as an effective hole transporting material in many different organic semiconductor devices for well over a decade. However, despite having many strong features which make this material such a popular hole transport/injection layer, PEDOT:PSS is well-known to cause degradation in devices and limit their stability due to the acidity of the PSS chain. This review focusses on the attempts that have been made to combat this problem, with different strategies explored, including the development of neutral analogues, use of alternative materials and the introduction of barrier layers to prevent degradation of the electrode. Since solution-processing is a key advantage of using PEDOT:PSS, we concentrate on analogous materials that can also be solution-processed, with particular attention on whether orthogonal processing can be retained. We intend this work to be a useful guide for researchers considering enhanced device lifetimes, an important parameter when considering organic semiconductor devices for commercialisation.

The development of organic down-converting materials continues to attract attention in hybrid LED technology by obviating the need for non-sustainable rare-earth elements. In this work, a benzodiimidazole-based system (TPA-BDI) has been employed as a down-converting layer in a hybrid organic-inorganic LED device. A commercially available poly(urethane)-based resin is used as the encapsulating material, providing a dilute layer of TPA-BDI that is deposited on top of the GaN-based LED. Crucially, the solution-state emissive performance is generally maintained when encapsulated at low concentrations within this resin. A maximum luminous efficacy of 87 lm W -1 was demonstrated using a 1.0 mg ml -1 concentration of TPA-BDI in the resin. The suitability of using organic down-converters to produce green light from hybrid devices was demonstrated by the excellent repeatability of the device characteristics across a series of encapsulated LEDs.

The quenching of excitons in organic solar cells can play a significant role in limiting their power conversion efficiency (PCE). In this article, we investigate the effect of a thin layer of hexapropyltruxene inserted at the interface between the electron donor boron subphthalocyanine chloride (SubPc) and its underlying hole contact in planar heterojunction solar cells. We find that a 3.8 nm hexapropyltruxene interlayer between the molybdenum oxide (MoOx) hole contact and SubPc is sufficient to improve PCE in SubPc/C60 fullerene solar cells from 2.6% to 3.0%, a ∼20% performance improvement. While the absorption stays roughly the same, the comparison of external and internal quantum efficiencies reveals a significant increase in SubPc's contribution to the current for light with wavelengths between 520 and 600 nm. Microstructure and surface morphology assessed with in situ Grazing-Incidence Wide-Angle X-Ray Scattering (GIWAXS) and Atomic Force Microscopy (AFM), are evaluated alongside in situ spectroscopic ellipsometry, and photoluminescence measurements. The microstructural investigations demonstrate changes to the surface and bulk of SubPc grown atop a hexapropyltruxene interlayer indicating that the latter acts as a template layer in a similar way as MoOx. However, the improvement in PCE is found to be mainly via reduced exciton quenching at the MoOx contact with the insertion of the hexapropyltruxene layer.

International audience; A facile efficient synthetic tool, Buchwald-Hartwig cross-coupling reaction, for the functionalization of 1,2,4,5tetrazines is presented. Important factors affecting the Buchwald-Hartwig cross-coupling reaction have been optimized. Seven new donor-acceptor tetrazine molecules (TA1-TA7) were conveniently prepared in good to high yields (61%-72%). They have been subsequently engaged in inverse Electron Demand Diels-Alder (iEDDA) reaction with cyclooctyne. The photophysical and electrochemical properties of the new pyridazines have been studied. Some are fluorescent acting as turn-on probes. More importantly two pyridazines (DA3 and DA6) exhibit room temperature phosphorescence (RTP) properties.

Conjugated polymers are an important class of organic semiconductors that can be deposited from solution to make optoelectronic devices. Among them, poly(9,9′-dioctylfluorene) (PFO) has distinctive optical properties arising from its ability to adopt an ordered planar conformation (β phase) from a disordered glassy phase (α phase). The β phase has attractive optical properties, but the precise mechanism of its formation in solution remains unknown. Here, we have combined specifically tailored polymer synthesis and surface-passivation strategies to provide the first spectroscopic characterization of single PFO chains in solution at room temperature. By anchoring PFO molecules at one end on an anti-adherent surface, we show that isolated chains can adopt the β-phase conformation in a solvent-dependent manner. Furthermore, we find that individual PFO chains can reversibly switch multiple times between phases in response to solvent-exchange events. The methodology presented here for polymer synthesis and immobilization is widely applicable to investigate other luminescent polymers. Postprint Postprint

Using a simple -conjugated trimer, EDOT-phenylene-EDOT (where EDOT = 3,4-ethylenedioxythiophene), we evaluate the effect that fluorine substituents have upon changes in conformation, conjugation and oxidation potentials in -conjugated structures. These variations are assessed as a function of the fluorine atom’s propensity to feature in hydrogen and/or halogen bonding with other heteroatoms. The molecular motif was chosen because the EDOT unit presents the possibility of competing O···X or S···X non-covalent contacts (where X = H or F). Such non-bonding interactions are acknowledged to be highly influential in dictating molecular and polymer morphology and inducing changes in certain physical properties. We have studied four compounds, beginning with an unsubstituted bridging phenylene ring and then adding one, two or four fluorine units to the parent molecule. Our studies involve single crystal XRD studies, cyclic voltammetry, absorption spectroscopy and density functional theory calculations to identify the dominant non-covalent interactions and elucidate their effects on the molecules described. Experimental studies have also been carried out on the corresponding electrochemically synthesized polymers to confirm that these non-covalent interactions and their effects persist in polymers. Our findings show that hydrogen bonding and halogen bonding feature in these molecules and their corresponding polymers. ABSTRACT: Using a simple -conjugated trimer, EDOT-phenylene-EDOT (where EDOT = 3,4-ethylenedioxythiophene), we evaluate the effect that fluorine substituents have upon changes in conformation, conjugation and oxidation potentials in -conjugated structures. These variations are assessed as a function of the fluorine atom’s propensity to feature in hydrogen and/or halogen bonding with other heteroatoms. The molecular motif was chosen because the EDOT unit presents the possibility of competing O···X or S···X non-covalent contacts (where X = H or F). Such non-bonding interactions are acknowledged to be highly influential in dictating molecular and polymer morphology and inducing changes in certain physical properties. We have studied four compounds, beginning with an unsubstituted bridging phenylene ring and then adding one, two or four fluorine units to the parent molecule. Our studies involve single crystal XRD studies, cyclic voltammetry, absorption spectroscopy and density functional theory calculations to identify the dominant non-covalent interactions and elucidate their effects on the molecules described. Experimental studies have also been carried out on the corresponding electrochemically synthesized polymers to confirm that these non-covalent interactions and their effects persist in polymers. Our findings show that hydrogen bonding and halogen bonding feature in these molecules and their corresponding polymers.

Low-cost single molecular electrochromic (EC) materials with low toxicity are desirable for EC displays and photonic devices. In this study, new EC materials based on phthalates, an inexpensive class of benzoate materials with relatively simple molecular structure, are designed and prepared. Despite being good candidates for EC devices due to clear colour changes when reduced, devices fabricated using phthalate derivatives (PDs) suffer from a high driving voltage. Herein, we propose a facile strategy of replacing the benzene core with polyaromatic esters to enlarge the conjugated area and to synthesise PDs to lower the driving voltage in EC devices. Additionally, devices show good memory effect (hundreds of seconds), the ability to undergo multiple colour changes and enhanced stability, dependent on the size of the conjugated bridge between the two sides of the molecule. The fabricated EC devices based on polyaromatic esters demonstrate a low driving voltage (−2.6 V). We have shown that the number of aromatic ester rings in the conjugated area is very critical to obtain different colours in this new class of EC materials. This series of EC materials has promising potential for future industry applications due to the vivid colour change upon electrochemical stimulation at a low driving voltage.

P.J.S. and A.L.K. thank the EPSRC for funding under Grants EP/R03480X/1, EP/P02744X/2, and EP/N009908/2. One of the most desirable and advantageous attributes of organic materials chemistry is the ability to tune the molecular structure to achieve targeted physical properties. This can be performed to achieve specific values for the ionization potential or electron affinity of the material, the absorption and emission characteristics, charge transport properties, phase behavior, solubility, processability, and many other properties, which in turn can help push the limits of performance in organic semiconductor devices. A striking example is the ability to make subtle structural changes to a conjugated macromolecule to vary the absorption and emission properties of a generic chemical structure. In this Account, we demonstrate that target properties for specific photonic applications can be achieved from different types of semiconductor structures, namely, monodisperse star-shaped molecules, complex linear macromolecules, and conjugated polymers. The most appropriate material for any single application inevitably demands consideration of a trade-off of various properties; in this Account, we focus on applications such as organic lasers, electrogenerated chemiluminescence, hybrid light emitting diodes, and visible light communications. In terms of synthesis, atom and step economies are also important. The star-shaped structures consist of a core unit with 3 or 4 functional connection points, to which can be attached conjugated oligomers of varying length and composition. This strategy follows a convergent synthetic pathway and allows the isolation of target macromolecules in good yield, high purity, and absolute reproducibility. It is a versatile approach, providing a wide choice of constituent molecular units and therefore varying properties, while the products share many of the desirable attributes of polymers. Constructing linear conjugated macromolecules with multifunctionality can lead to complex synthetic routes and lower atom and step economies, inferior processability, and lower thermal or chemical stability, but these materials can be designed to provide a range of different targeted physical properties. Conventional conjugated polymers, as the third type of structure, often feature so-called “champion” properties. The synthetic challenge is mainly concerned with monomer synthesis, but the final polymerization sequence can be hard to control, leading to variable molecular weights and polydispersities and some degree of inconsistency in the properties of the same material between different synthetic batches. If a champion characteristic persists between samples, then the variation of other properties between batches can be tolerable, depending on the target application. In the case of polymers, we have chosen to study PPV-type polymers with bulky side groups that provide protection of their conjugated backbone from π–π stacking interactions. These polymers exhibit high photoluminescence quantum yields (PLQYs) in films and short radiative lifetimes and are an important benchmark to monodisperse star-shaped systems in terms of different absorption/emission regions. This Account therefore outlines the advantages and special features of monodisperse star-shaped macromolecules for photonic applications but also considers the two alternative classes of materials and highlights the pros and cons of each class of conjugated structure. Publisher PDF

A series of novel star-shaped oligofluorene-thiophene-tetrathiafulvalene systems have been synthesised, following different synthetic routes. Each system incorporates a tetrathiafulvalene redox-active centre and four oligofluorene arms, providing a two-dimensional character of the conjugated backbone. The oligomers differ in the number of fluorene units present in the arms (1 to 4) and the terminal groups at the end of each arm (H or trimethylsilyl). Half-unit oligofluorene systems possessing a 1,3-dithiole-2-one core (a known precursor to the tetrathiafulvalene centre) have been synthesised in order to compare the thermal, optical and electrochemical properties. These half-unit systems consist of a 1,3-dithiole-2-one core fused to a thiophene unit at the 3- and 4- positions. Two oligofluorene arms consisting of 1 to 4 monomer units per arm are positioned at the 4- and 6- positions of the thiophene unit, affording extended conjugation through the thiophene centre. The half-unit systems are found to be moderate emitters in the solution-state, however, the star-shaped systems bearing the tetrathiafulvalene core exhibit inhibited fluorescence in both the solution and solid states. We have demonstrated that the emission of the tetrathiafulvalene systems can be enhanced through the oxidation of the redox-centre followed by a consecutive reaction of the strongly electrophilic tetrathiafulvalene dication with such nucleophiles as water and hydrazine. The result of these reactions leads to an increase in the photoluminescence of these systems, affording the opportunity for the tetrathiafulvalene materials to be used as photonic materials in moisture indicators.

A series of red fluorescent materials (compounds 1-4), which each contain the symmetric fluorene-thiophene-BT-thiophene-fluorene core, is presented along with their performance in solution-processed OLED devices. Extending the molecular conjugation through end-capping with additional fluorene units (compound 2), or through incorporation of donor functionalities (compounds 3 and 4) improves OLED performance relative to the parent compound 1. Notably, incorporating triphenylamine donor groups in compound 3 led to solution-processed OLED devices operating with a peak luminance of 2888 cd m −2 and a low turn-on voltage (3.6 V).

One of the most important non-radiative relaxation processes that limits the quantum yield of a fluorophore is related to aggregation of the molecules in the solid-state causing excimer quenching. To limit this quenching mechanism, the fluorophore can be contained within a well-ordered 3D system that minimises aggregation through rigid bonds and spatial separation in a defined topological construct. Herein, the synthesis, characterisation and application as a down-converter of a new luminescent 3D material (MOF-BTBMBA) that incorporates a building block based on a benzothiadiazole (BT) derivative (BTBMBA) in a metal–organic framework (MOF) is presented. Notably, the photoluminescence quantum yield and hybrid LED performance are significantly improved for the MOF-based device compared to that prepared with the free ligand, highlighting the effectiveness of the rigid scaffold arrangement.

A series of star‐shaped oligofluorene molecules, each containing a TPE core, have been specifically designed and produced to show effective aggregation‐induced emission (AIE). Each molecule differs either in the number of fluorene units within the arms (e.g., 1 or 4, compounds 4 and 5), or the terminal group positioned at the end of each arm (e.g., H, TMS, or TPA, compounds 4, 6, and 7). Although they are all poor emitters in solution phase they become efficient yellow‐green luminogens in the condensed state. Their AIE properties were investigated in THF/H2O mixtures, with each molecule exhibiting a clear emission enhancement at specific water contents. An all‐organic distributed feedback (DFB) laser was fabricated using compound 4 as the gain material and exhibited an average threshold energy fluence of 60 ± 6 μJ/cm2 and emission in the green region. Furthermore, piezofluorochromism studies on a thin film of this material displayed a linear dependence of the amplified spontaneous emission (ASE) peak position on applied pressure, indicating potential applications as lasing‐based pressure sensors. © 2016 The Authors. Journal of Polymer Science Part A: Polymer Chemistry Published by Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 734–746

The authors wish to thank the EPSRC for funding. PJS thanks the Royal Society for a Wolfson Research Merit Award. 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. Publisher PDF

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.

With the increased and continuous threat of terrorist attacks in public areas, new sensors are required to safeguard the public from homemade explosive devices. Current commercial sensors for explosive vapors are high-cost, bulky equipment, not amenable to mass production, thus limiting their widespread deployment within society. We are conducting research on polymer-based microsensors that can overcome these limitations. Our devices offer an approach to the realization of low-cost sensors that can readily be placed as a network of electronic sentinels that can be permanently located in the areas of public access. The polymers are chemically tailored to have a high affinity for nitro and peroxide vapors and are grown electrochemically on microelectrodes. Novel nanoporous polymer-based sensors are demonstrated with a detection level of 200 ppb of nitro vapors. In addition, a prototype reversible sensor for peroxide vapors is demonstrated to low ppm concentrations.

The synthesis and characterisation of two novel organic down-converting molecules is disclosed, together with their performance as functional colour-converters in combination with inorganic blue light-emitting diodes (LEDs). Each molecule contains two fluorene-triphenylamine arms, connected to either a benzothiadiazole or bisbenzothiadiazole core. These molecules have been selected on the basis that they are free from absorption bands in the green region of the visible spectrum to maximise their performance and offer improvements compared with previous BODIPY-containing analogues. The inorganic InGaN/GaN LED emits at 444 nm, overlying the absorption of each of the organic molecules. The combination of the blue (inorganic) and yellow (organic) emission is shown to produce reasonable quality, white light-emitting hybrid devices for both down-converter molecules. Cool to warm white light is achieved for both molecules by increasing the concentration. An optimum colour rendering index (CRI) value of 66 is obtained for the mono-benzothiadiazole molecule. Also a high blue-to-white efficacy (defined as white luminous flux (lm)/blue radiant flux (W)) of 368 lm W$^{-1}$ is achieved, superseding the current phosphor converters of 200-300 lm W$^{-1}$. A comparison of these down-converting molecules to the older generation BODIPY-containing molecules is also provided.

Three simple semiconducting acceptor–donor–acceptor (A–D–A) small molecules based on an electron-rich (3,4-ethylenedioxythiophene) EDOT central core have been synthesised (DIN-2TE, DRH-2TE, DECA-2TE) and characterised. Organic photovoltaic (OPV) devices incorporating these materials have been prepared and evaluated. The physical properties of the molecules were characterised by TGA, DSC, UV/vis spectroscopy and cyclic voltammetry. The optical HOMO–LUMO energy gaps of the molecules in the solid state were in the range 1.57–1.82 eV, and in solution 1.88–2.04 eV. Electrochemical HOMO–LUMO energy gaps determined by cyclic voltammetry were found to be in the range 1.97–2.31 eV. The addition of 1% 1,8-diiodooctane (DIO) to photoactive blends of the A–D–A molecules and PC71BM more than doubled the power conversion efficiency (PCE) in the case of DRH-2TE:PC71BM devices to 1.36%.

This paper presents the novel use of spray-coating to fabricate organic solar cells on fabrics for wearable energy harvesting applications. The surface roughness of a standard woven 65/35 polyester cotton fabric used in this work is of the order of 150 μm and this is reduced to a few microns by a screen printed interface layer. This pre-treated fabric substrate with reduced surface roughness was used as the target substrate for the spray-coated fabric organic solar cells that contain multiple layers of electrodes and active materials. Fully spray-coated photovoltaic (PV) devices fabricated on fabric substrates have been successfully demonstrated with power conversion efficiency comparable to that of their glass based counterparts. All PV devices are characterised under simulated AM 1.5 conditions. Device morphologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). This approach is potentially suitable for the low cost integration of PV devices into clothing and other decorative textiles.

We consider the roles of heteroatoms (mainly nitrogen, the halogens and the chalcogens) in dictating the conformation of linear conjugated molecules and polymers through non-covalent intramolecular interactions. Whilst hydrogen bonding is a competitive and sometimes more influential interaction, we provide unambiguous evidence that heteroatoms are able to determine the conformation of such materials with reasonable predictability.

We report the fabrication and characterization of a mechanically flexible 4 × 4 array of organic semiconductor lasers using blue-emitting tris(trifluorene)truxene oligomers as the gain medium. The device was fabricated entirely by soft lithography from the reproduction of a 1-D silica master grating. The grating array pattern was created directly on the master by a polymeric mask. Each element, or pixel, of the resulting laser array is made of a polymer mesa with embedded surface grating, and all the array elements are on the same mechanically flexible platform. Laser oscillation thresholds of individual photopumped laser pixels are as low as 75 nJ (70 μJ/cm2 or 14 kW/cm2). The emission wavelength uniformity of the array is within ±3 nm with individual laser pixels emitting from 432 to 438 nm. On mechanical flexing of the array, a 10-nm tuning of the emission wavelength is achieved and is attributed to a change in the grating periodicity.

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.

A series of selenophene oligomers incorporating conjugated fluorinated phenylene units have been synthesised as potential semiconductor materials for organic field-effect transistors (OFETs). X-ray crystallography shows that the molecules are held in close proximity by several short intermolecular contacts, making them ideal candidates for OFET applications.

Current commercial sensors for explosive vapours are high cost bulky equipment not amenable to mass production and thus prevents their mass deployment within society. Our research objective is to create compact sensors that are not only portable but of such low cost that they can be installed in buildings in the same way as smoke detectors. We have developed novel polymers whose properties have been tailored to give them a higher affinity to target nitro group (NO2) bearing molecules associated with explosives. The polymers have been grown electrochemically onto miniature interdigitated electrode platforms yielding miniature sensors. Novel porous polymers based sensors are demonstrated which yield a detection level of 200 ppb of nitro vapours and can be manufactured at low-unit-cost.

This work is part of the TIRAMISU project, funded by the European Commission’s Seventh Framework Programme (FP7/2007-2013) under grant agreement n◦284747 and the Engineering and Physical Sciences Research Council (EPSRC) grants EP/J009016/1 and EP/F059922/1. I.D.W.S. and P.J.S. are Royal Society Wolfson Research Merit Award holders. The density of organic semiconductor films is an important quantity because it is related to intermolecular spacing which in turn determines the electronic and photophysical properties. We report thin film density and refractive index measurements of polyfluorenes and star-shaped oligofluorene truxene molecules. An ellipsometer and a procedure using a spectrophotometer were used to determine film thickness and mass of spin-coated films, respectively. We present a study of the effect of alkyl side-chain length on the volumetric mass density and refractive index of the materials studied. The density measured for poly(9,9-di-n-octylfluorene) (PF8) was 0.88 ± 0.04 g/cm3 and decreased with longer alkyl side chains. For the truxene molecule with butyl side chains (T3 butyl), we measured a density of 0.90 ± 0.04 g/cm3, which also decreased with increasing side-chain length. Postprint

The authors thank EPSRC for fi nancial support from the UP-VLC project grant (EP/K00042X/1). P.J.S. and I.D.W.S. also acknowledge a Royal Society Wolfson Research Merit Award. Star-shaped organic semiconductors with boron dipyrromethene (BODIPY) cores are color-conversion materials for blue LED-based visible light communications. The difference between 0 and 1 bits is resolved in colour-converted data links at 100 Mb s−1. The BODIPY modulation bandwidth is eight times higher than that measured using conventional phosphor color converters. Publisher PDF

The authors thank EPSRC for financial support from UP-VLC Project Grant (EP/K00042X/1). Visible Light Communications (VLC) is a promising new technology which could offer higher data transmission rates than existing broadband RF/microwave wireless technologies. In this paper, we show that a blend of semiconducting polymers can be used to make a broadband, balanced color converter with a very high modulation bandwidth to replace commercial phosphors in hybrid LEDs for visible light communications. The resulting color converter exploits partial Förster energy transfer in a blend of the highly fluorescent green emitter BBEHP-PPV and orange-red emitting MEH-PPV. We quantify the efficiency of the photoinduced energy transfer from BBEHP-PPV to MEH-PPV, and demonstrate modulation bandwidths (electrical-electrical) of ∼200 MHz, which are 40 times higher than commercially available phosphor LEDs. Furthermore, the VLC data rate achieved with this blend using On-Off Keying (OOK) is many times (∼35) higher than that measured with a commercially available phosphor color converter. Postprint

Nonlinear optical response in organic semiconductors has been an attractive property for many practical applications. For frequency up-converted lasers, to date, conjugated polymers, fluorescent dyes and small organic molecules have been proposed but their performances have been severely limited due to the difficulty in simultaneously achieving strong nonlinear optical response and high performance optical gain. In this work, we show that structurally designed truxene-based star-shaped oligofluorenes exhibit strong structure-property relationships enabling enhanced nonlinear optical response with favorable optical gain performance. As the number of fluorene repeat units in each arm is increased from 3 to 6, these molecules demonstrate a two-photon absorption cross-section as high as 2200 GM, which is comparable to that of linear conjugated polymers. Tailored truxene oligomers with six fluorene units in each arm (T6) show two-photon absorption pumped amplified spontaneous emission with a threshold as low as 2.43 mJ cm-2, which is better than that of the lowest reported threshold in organic semiconductors. Furthermore, we show a frequency up-converted laser using the newly designed and synthesized star-shaped oligomer T6 with a threshold as low as 3.1 mJ cm-2, which is more than an order of magnitude lower than that of any conjugated polymer. Thus, these oligomers with enhanced nonlinear optical properties are highly attractive for bio-integrated applications such as photodynamic therapy and in vivo bio-sensing. © The Royal Society of Chemistry 2015.

The incorporation of 2,1,3-benzothiadiazole units within the arms of a trigonal quarterfluorene–truxene star-shaped system leads to a monodisperse material with stable multi-electron p- and n-doped states and highly efficient yellow electrogenerated chemiluminescence (ECL). The quantum yield for ECL is 7 times greater than that of the common blue ECL emitter 9,10-diphenylanthracene (DPA).

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.

A series of hybrid tetrathiafulvalene-oligothiophene compounds has been synthesised, where the tetrathiafulvalene unit is fused at each side to an end-capped oligothiophene chain of varying length (terthiophene, quinquithiophene and septithiophene). Each hybrid structure (1-3) has been studied by cyclic voltammetry and triple EPR-UV-Vis-NIR spectroelectrochemistry in the case of the quinquithiophene compound (2). Comparison is made with the corresponding half-units, which lack the fulvalene core and contain just one oligothiophene chain. The highest hole mobility of quinquithiophene-TTF 2 was obtained from field effect transistors (8.61 × 10-3 cm 2 V-1 s-1); its surface morphology was characterised by tapping mode atomic force microscopy and a power conversion of 2.5% was achieved from a bulk heterojunction organic solar cell device using PC71BM as the acceptor.

The first example of an all-organic oligofluorene truxene based distributed feedback laser for the detection of a specific protein–small molecule interaction is reported. The protein avidin was detected down to View the MathML source1μgmL−1 using our biotin-labelled biosensor platform. This interaction was both selective and reversible when biotin was replaced with desthiobiotin. Avidin detection was not perturbed by Bovine Serum Albumin up to View the MathML source50,000μgmL−1. Our biosensor offers a new detection platform that is both highly sensitive, modular and potentially re-usable.