Electrically driven organic laser using integrated OLED pumping.

Organic semiconductors are carbon-based materials that combine optoelectronic properties with simple fabrication and the scope for tuning by changing their chemical structure. They have been successfully used to make organic light-emitting diodes (OLEDs, now widely found in mobile phone displays and televisions), solar cells, transistors and sensors. However, making electrically driven organic semiconductor lasers is very challenging.

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.

Lest We Forget-The Importance of Heteroatom Interactions in Heterocyclic Conjugated Systems, from Synthetic Metals to Organic Semiconductors.

The field of synthetic metals is, and remains, highly influential for the development of organic semiconductor materials. Yet, with the passing of time and the rapid development of conjugated materials in recent years, the link between synthetic metals and organic semiconductors is at risk of being forgotten. This review reflects on one of the key concepts developed in synthetic metals - heteroatom interactions.

Introducing a new 7-ring fused diindenone-dithieno[3,2-:2',3'-]thiophene unit as a promising component for organic semiconductor materials.

A novel π-conjugated molecule, is reported, which is fused, rigid, and planar, featuring the electron-rich dithieno[3,2-:2',3'-]thiophene (DTT) unit in the core of the structure. Adjacent to the electron-donating DTT core, there are indenone units with electron-withdrawing keto groups. To enable solubility in common organic solvents, the fused system is flanked by ethylhexylthiophene groups.

Polycentric binding in complexes of trimethylamine--oxide with dihalogens.

Dihalogens readily interact with trimethylamine--oxide under ambient conditions. Accordingly, herein, stable 1 : 1 adducts were obtained in the case of iodine chloride and iodine bromide. The crystal and molecular structure of the trimethylamine--oxide-iodine chloride adduct was solved.

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.

Multiple Noncovalent Bonding in Halogen Complexes with Oxygen Organics. I. Tertiary Amides.

The present work describes the structure and binding of adducts of N,N'-diacetylpiperazine with halogens and interhalogens based on combination of different experimental methods and quantum chemical calculations. On the basis of conductometric and spectro-photometric experimental results, behavior of complexes in the acetonitrile solution was described. The iodine adduct with N,N'-diacetylpiperazine fully degrades into components.

Chirality induction using circularly polarized light into a branched oligofluorene derivative in the presence of an achiral aid molecule.

Chirality induction into a uniform, star-shaped fluorene oligomer with a central truxene moiety (T3) was achieved using circularly polarized light in the presence of achiral fluorene or phenanthrene. Induction into T3 alone was difficult, suggesting that close chain packing realized through interactions of T3 with small molecules plays a role in chirality induction.

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.

Thiazole-induced rigidification in substituted dithieno-tetrathiafulvalene: the effect of planarisation on charge transport properties.

Two novel tetrathiafulvalene (TTF) containing compounds 1 and 2 have been synthesised via a four-fold Stille coupling between a tetrabromo-dithienoTTF 5 and stannylated thiophene 6 or thiazole 4. The optical and electrochemical properties of compounds 1 and 2 have been measured by UV-vis spectroscopy and cyclic voltammetry and the results compared with density functional theory (DFT) calculations to confirm the observed properties. Organic field effect transistor (OFET) devices fabricated from 1 and 2 demonstrated that the substitution of thiophene units for thiazoles was found to increase the observed charge transport, which is attributed to induced planarity through S-N interactions of adjacent thiazole nitrogen atoms and TTF sulfur atoms and better packing in the bulk.

An Air-Stable DPP-thieno-TTF Copolymer for Single-Material Solar Cell Devices and Field Effect Transistors.

Following an approach developed in our group to incorporate tetrathiafulvalene (TTF) units into conjugated polymeric systems, we have studied a low band gap polymer incorporating TTF as a donor component. This polymer is based on a fused thieno-TTF unit that enables the direct incorporation of the TTF unit into the polymer, and a second comonomer based on the diketopyrrolopyrrole (DPP) molecule. These units represent a donor-acceptor copolymer system, p(DPP-TTF), showing strong absorption in the UV-visible region of the spectrum.

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.

Novel electrochemiluminescent materials for sensor applications.

Electrochemiluminescence (ECL) uses redox reactions to generate light at an electrode surface, and is gaining increasing attention for biosensor development due to its high sensitivity and excellent signal-to-noise ratio. ECL studies of monodisperse oligofluorene-truxenes (T4 series) have been reported previously, showing the production of stable radical cations and radical anions, generating blue ECL. The compound in this study differs from the original structures, in that there are 2,1,3-benzothiadazole (BT) units inserted between the first and second fluorene units of the quarterfluorenyl arms.

Conducting nanofibers and organogels derived from the self-assembly of tetrathiafulvalene-appended dipeptides.

We demonstrate the nonaqueous self-assembly of a low-molecular-mass organic gelator based on an electroactive p-type tetrathiafulvalene (TTF)-dipeptide bioconjugate. We show that a TTF moiety appended with diphenylalanine amide derivative (TTF-FF-NH2) self-assembles into one-dimensional nanofibers that further lead to the formation of self-supporting organogels in chloroform and ethyl acetate. Upon doping of the gels with electron acceptors (TCNQ/iodine vapor), stable two-component charge transfer gels are produced in chloroform and ethyl acetate.

Hybrid organic semiconductor lasers for bio-molecular sensing.

Bio-functionalised luminescent organic semiconductors are attractive for biophotonics because they can act as efficient laser materials while simultaneously interacting with molecules. In this paper, we present and discuss a laser biosensor platform that utilises a gain layer made of such an organic semiconductor material. The simple structure of the sensor and its operation principle are described.

An oligofluorene truxene based distributed feedback laser for biosensing applications.

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 1 μg mL(-1) using our biotin-labelled biosensor platform. This interaction was both selective and reversible when biotin was replaced with desthiobiotin.

LED pumped polymer laser sensor for explosives.

A very compact explosive vapor sensor is demonstrated based on a distributed feedback polymer laser pumped by a commercial InGaN light-emitting diode. The laser shows a two-stage turn on of the laser emission, for pulsed drive currents above 15.7 A.

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.

Nanoimprinted polymer lasers with threshold below 100 W/cm2 using mixed-order distributed feedback resonators.

Organic semiconductor lasers were fabricated by UV-nanoimprint lithography with thresholds as low as 57 W/cm(2) under 4 ns pulsed operation. The nanoimprinted lasers employed mixed-order distributed feedback resonators, with second-order gratings surrounded by first-order gratings, combined with a light-emitting conjugated polymer. They were pumped by InGaN LEDs to produce green-emitting lasers, with thresholds of 208 W/cm(2) (102 nJ/pulse).

Nanoimprinted organic semiconductor laser pumped by a light-emitting diode.

An organic semiconductor laser, simply fabricated by UV-nanoimprint lithography (UV-NIL), that is pumped with a pulsed InGaN LED is demonstrated. Molecular weight optimization of the polymer gain medium on a nanoimprinted polymer distributed feedback resonator enables the lowest reported UV-NIL laser threshold density of 770 W cm(-2) , establishing the potential for scalable organic laser fabrication compatible with mass-produced LEDs.

Dynamics of fluorescence depolarisation in star-shaped oligofluorene-truxene molecules.

Star-shaped molecules are of growing interest as organic optoelectronic materials. Here a detailed study of their photophysics using fluorescence depolarisation is reported. Fluorescence depolarisation dynamics are studied in branched oligofluorene-truxene molecules with a truxene core and well-defined three-fold symmetry, and are compared with linear fluorene oligomers.

Effect of exciton self-trapping and molecular conformation on photophysical properties of oligofluorenes.

Electronic absorption and fluorescence transitions in fluorene oligomers of differing lengths are studied experimentally and using density functional theory (DFT) and time-dependent DFT. Experimental values are determined in two ways: from the measured molar absorption coefficient and from the radiative rate deduced from a combination of fluorescence quantum yield and lifetime measurements. Good agreement between the calculated and measured transition dipoles is achieved.