Ana I. S. Neves

A new hybrid material exhibiting room temperature spin-crossover and ferromagnetic cluster-glass behavior

A new compound, [Fe(5–Cl-qsal)2][Ni(α-tpdt)2].CH3CN, where α-tpdt = 2,3-thiophenedithiolate and H5–Cl-qsal = N-(8-quinolyl)-5-chlorosalicylaldimine, was prepared and structurally and magnetically characterized. The crystal structure is based on an arrangement of alternate layers of [Fe(5–Cl-qsal)2]+ cations and [Ni(α-tpdt)2]− anions. The magnetic measurements and Mossbauer spectroscopy revealed hybrid behavior in this compound, where a ferromagnetic cluster-glass behavior, ascribed to the anions network, and a spin crossover (SCO) of the [Fe(5–Cl-qsal)2]+ cations were observed. The glassy behavior, with a blocking temperature of ca. 7.5 K, results from the disorder in the anionic layer and the competition between ferro- and antiferromagnetic interactions in the anionic layers. The SCO process with T1/2 = 298 K (high spin fraction = γHS = 0.5) is rather sluggish in the limits of the conversion (γHS ∼ 0 and γHS ∼ 1), which is attributed to the effect of the anions that seem to restrict somehow the structural distortions of the cations associated with the SCO process.

(α-DT-TTF)2[Au(mnt)2]: a weakly disordered molecular spin-ladder system.

The synthesis and characterization of (α-DT-TTF)2[Au(mnt)2] is reported. The magnetic properties of this new salt show that it is still a rare example of an organic spin-ladder. (α-DT-TTF)2[Au(mnt)2] shares the same ladder structure of the DT-TTF and ETT-TTF analogues, and its room temperature conductivity is ∼2 S/cm. Despite the observed donor orientation disorder associated with the thiophenic sulfur atoms, the intermolecular interactions between donor units, calculated using the extended Hückel approximation and a double-ξ basis set, show that the interaction values do not depend on the configuration of the sulfur atom on the thiophenic ring. The insensitivity of the spin-ladder magnetic properties to the donor molecular disorder in (α-DT-TTF)2[Au(mnt)2] is a direct consequence of the negligible contribution of the disordered thiophenic sulfur atom to the HOMO. In the related donor ETT-TTF, this contribution is significant and destroys the magnetic interactions, and no spin-ladder is observed. This compound not only enlarges the number of organic spin-ladder systems in this series of closely related compounds but also provides an interesting example of weakly disordered molecular spin-ladder system.

Towards conductive textiles: coating polymeric fibres with graphene

Conducting fibres are essential to the development of e-textiles. We demonstrate a method to make common insulating textile fibres conductive, by coating them with graphene. The resulting fibres display sheet resistance values as low as 600 Ωsq−1, demonstrating that the high conductivity of graphene is not lost when transferred to textile fibres. An extensive microscopic study of the surface of graphene-coated fibres is presented. We show that this method can be employed to textile fibres of different materials, sizes and shapes, and to different types of graphene. These graphene-based conductive fibres can be used as a platform to build integrated electronic devices directly in textiles.

Ultrasensitive organic phototransistors with multispectral response based on thin-film/single-crystal bilayer structures

We report on highly efficient organic phototransistors (OPTs) based on thin-film/single-crystal planar bilayer junctions between 5,6,11,12-tetraphenyltetracene (rubrene) and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM). The OPTs show good field-effect characteristics in the dark, with high hole-mobility (4–5 cm2 V−1 s−1), low-contact resistance (20 kΩ cm), and low-operating voltage (≤5 V). Excellent sensing capabilities allow for light detection in the 400–750 nm range, with photocurrent/dark current ratio as high as 4 × 104, responsivity on the order of 20 AW−1 at 27 μW cm−2, and an external quantum efficiency of 52 000%. Photocurrent generation is attributed to enhanced electron and hole transfer at the interface between rubrene and PC61BM, and fast response times are observed as a consequence of the high-mobility of the interfaces. The optoelectronic properties exhibited in these OPTs outperform those typically provided by a-Si based devices, enabling future applications where multifunctionality in a single-device is sought.

Cation and ligand roles in the coordination of FeIII bisdithiolene complexes; the crystal structures of (BrBzPy)2[Fe(qdt)2]2 and [Fe(α-tpdt)2]22− salts

The crystal structure of the new (BrBzPy)2[Fe(qdt)2]2 complex (qdt = quinoxalinedithiolate) shows a rare weak FeIII bisdithiolene dimerisation with unusual molecular planarity and long apical S–Fe distances. This anion configuration is intermediate between the only monomeric Fe bisdithiolene reported so far, with isolated square planar [Fe(qdt)2]− units, and the common strong dimeric geometry also observed in other [Fe(qdt)2]2 salts. The standard strong dimeric situation is also observed in the [Fe(α-tpdt)2]2 salt (α-tpdt = 2,3-thiophenedithiolate) with the same cation, as well as with n-Bu4N and Et4N showing the influence of different ligands and cations on the coordination geometry and supramolecular structure of the FeIII complexes.

A New Facile Route to Flexible and Semi-Transparent Electrodes Based on Water Exfoliated Graphene and their Single-Electrode Triboelectric Nanogenerator

Wearable technologies are driving current research efforts to self-powered electronics, for which novel high-performance materials such as graphene and low-cost fabrication processes are highly sought.The integration of high-quality graphene films obtained from scalable water processing approaches in emerging applications for flexible and wearable electronics is demonstrated. A novel method for the assembly of shear exfoliated graphene in water, comprising a direct transfer process assisted by evaporation of isopropyl alcohol is developed. It is shown that graphene films can be easily transferred to any target substrate such as paper, flexible polymeric sheets and fibers, glass, and Si substrates. By combining graphene as the electrode and poly(dimethylsiloxane) as the active layer, a flexible and semi-transparent triboelectric nanogenerator (TENG) is demonstrated for harvesting energy. The results constitute a new step toward the realization of energy harvesting devices that could be integrated with a wide range of wearable and flexible technologies, and opens new possibilities for the use of TENGs in many applications such as electronic skin and wearable electronics.

Graphene electronic fibres with touch-sensing and light-emitting functionalities for smart textiles

The true integration of electronics into textiles requires the fabrication of devices directly on the fibre itself using high-performance materials that allow seamless incorporation into fabrics. Woven electronics and opto-electronics, attained by intertwined fibres with complementary functions are the emerging and most ambitious technological and scientific frontier. Here we demonstrate graphene-enabled functional devices directly fabricated on textile fibres and attained by weaving graphene electronic fibres in a fabric. Capacitive touch-sensors and light-emitting devices were produced using a roll-to-roll-compatible patterning technique, opening new avenues for woven textile electronics. Finally, the demonstration of fabric-enabled pixels for displays and position sensitive functions is a gateway for novel electronic skin, wearable electronic and smart textile applications.Wearable electronics: graphene textiles get really smartComplex functionalities have been brought on to the graphene coated textile fibres in a roll-to-roll-compatible fashion for the first time. A collaborative team led by Monica F. Craciun from University of Exeter, UK employs a ‘roll-to-roll’ like method to fabricate graphene-based transparent and flexible functional devices on textile fibres. The scientists develop a universal approach to pattern the graphene in various forms on the tape-shaped polypropylene fibres via a sacrificial photoresist layer. This creates a versatile platform for efficient device prototyping: functional devices such as capacitive touch-sensors and light-emitting device arrays can then be easily integrated. Their methods show high compatibility with industrial scale roll-to-roll and printing techniques, opening the gateway to smart multi-functional textile electronics in the future.

Smart textile: Exploration of wireless sensing capabilities

E-textile is a developing technology joining the advantages of material science and information and communication technologies. In this work, we present the development and assessment of smart textile system containing sensing, processing and wireless communication capabilities. We demonstrate a wearable temperature sensing system based on resistance temperature detection approach utilizing graphene technology, which allows high flexibility and robustness of the electronic textile. The developed sensing system demonstrates experimental sensitivity as high as 80Q/°C within the temperature detection range from 24 °C to 35 °C, which is the highest reported to date for wearable temperature sensors. In terms of wireless communication, the system operates at 2.4 GHz supporting Bluetooth low energy technology and securely transmits the measured data for up to 10 m which is proved by received signal strength and link quality indicators.

CCDC 725675: Experimental Crystal Structure Determination

Related Article: A.I.S.Neves, J.C.Dias, B.J.C.Vieira, I.C.Santos, M.B.C.Branco, L.C.J.Pereira, J.C.Waerenborgh, M.Almeida, D.Belo, V.da Gama|2009|CrystEngComm|11|2160|doi:10.1039/b906620a