Thin deposits and patterning of room-temperature-switchable one-dimensional spin-crossover compounds

"Liquid-liquid-solid"-type superoleophobic surfaces to pattern polymeric semiconductors towards high-quality organic field-effect transistors

Precisely aligned organic-liquid-soluble semiconductor microwire arrays have been fabricated by "liquid-liquid-solid" type superoleophobic surfaces directed fluid drying. Aligned organic 1D micro-architectures can be built as high-quality organic field-effect transistors with high mobilities of >10 cm(2) ·V(-1) ·s(-1) and current on/off ratio of more than 10(6) . All these studies will boost the development of 1D microstructures of organic semiconductor materials for potential application in organic electronics.

Logic-gate devices based on printed polymer semiconducting nanostripes

The applications of organic semiconductors in complex circuitry such as printed CMOS-like logic circuits demand miniaturization of the active structures to the submicrometric and nanoscale level while enhancing or at least preserving the charge transport properties upon processing. Here, we addressed this issue by using a wet lithographic technique, which exploits and enhances the molecular order in polymers by spatial confinement, to fabricate ambipolar organic field effect transistors and inverter circuits based on nanostructured single component ambipolar polymeric semiconductor. In our devices, the current flows through a precisely defined array of nanostripes made of a highly ordered diketopyrrolopyrrole-benzothiadiazole copolymer with high charge carrier mobility (1.45 cm(2) V(-1) s(-1) for electrons and 0.70 cm(2) V(-1) s(-1) for holes). Finally, we demonstrated the functionality of the ambipolar nanostripe transistors by assembling them into an inverter circuit that exhibits a gain (105) comparable to inverters based on single crystal semiconductors.

A simple method for fabricating patterned curvilinear microstructures in poly(dimethylsiloxane) by selective wetting

The fabrication of patterned microstructures in poly(dimethylsiloxane) (PDMS) is a prerequisite for soft lithography. Herein, curvilinear surface relief microstructures in PDMS are fabricated through a simple three-stage approach combining microcontact printing (μCP), selective surface wetting/dewetting and replica molding (REM). First, using an original PDMS stamp (first-generation stamp) with linear relief features, a chemical pattern on gold substrate is generated by μCP using hexadecanethiol (HDT) as an ink. Then, by a dip-coating process, an ordered polyethylene glycol (PEG) polymer-dot array forms on the HDT-patterned gold substrate. Finally, based on a REM process, the PEG-dot array on gold substrate is used to fabricate a second-generation PDMS stamp with microcavity array, and the second-generation PDMS stamp is used to generate third-generation PDMS stamp with microbump array. These fabricated new-generation stamps are utilized in μCP and in micromolding in capillaries (MIMIC), allowing the generation of surface micropatterns which cannot be obtained using the original PDMS stamp. The method will be useful in producing new-generation PDMS stamps, especially for those who want to use soft lithography in their studies but have no access to the microfabrication facilities.

Status and perspectives in thin films and patterning of spin crossover compounds

Spin crossover compounds are a class of functional materials able to switch their spin state upon external stimuli. They were proposed as potential candidates for several technological applications that require highly controlled thin films and patterns. Here we present a critical overview of the most important approaches for thin film growth and patterning of spin-crossover compounds, giving special attention to Fe(II) based molecules, which are the most studied materials. We present both conventional approaches to thin film growth (Langmuir-Blodgett, constructive chemical approach, spin coating, drop casting and vacuum sublimation) and patterning (combined top-down/bottom-up method, soft and unconventional lithography). We critically discuss the application of thin film growth and fabrication techniques highlighting the most critical aspects and the perspectives opened by the recent progress.

Pressure and temperature spin crossover sensors with optical detection

Iron(II) spin crossover molecular materials are made of coordination centres switchable between two states by temperature, pressure or a visible light irradiation. The relevant macroscopic parameter which monitors the magnetic state of a given solid is the high-spin (HS) fraction denoted n_HS, i.e., the relative population of HS molecules. Each spin crossover material is distinguished by a transition temperature T_1/2 where 50% of active molecules have switched to the low-spin (LS) state. In strongly interacting systems, the thermal spin switching occurs abruptly at T_1/2. Applying pressure induces a shift from HS to LS states, which is the direct consequence of the lower volume for the LS molecule. Each material has thus a well defined pressure value P_1/2. In both cases the spin state change is easily detectable by optical means thanks to a thermo/piezochromic effect that is often encountered in these materials. In this contribution, we discuss potential use of spin crossover molecular materials as temperature and pressure sensors with optical detection. The ones presenting smooth transitions behaviour, which have not been seriously considered for any application, are spotlighted as potential sensors which should stimulate a large interest on this well investigated class of materials.

Lattice effects on the spin-crossover profile of a mononuclear manganese(III) cation

Six solvated salts of a mononuclear manganese(III) complex with a chelating hexadentate Schiff base ligand are reported. One member of the series, [MnL]PF(6)⋅0.5 CH(3)OH (1), shows a rare low-spin (LS) electronic configuration between 10-300 K. The remaining five salts, [MnL]NO(3)⋅C(2)H(5)OH(2), [MnL]BF(4)⋅C(2)H(5)OH(3), [MnL]CF(3)SO(3)⋅C(2)H(5)OH (4), [MnL]ClO(4)⋅C(2)H(5)OH (5) and [MnL]ClO(4)⋅0.5 CH(3)CN (6), all show gradual incomplete spin-crossover (SCO) behaviour. The structures of all were determined at 100 K, and also at 293 K in the case of 3-6. The LS salt [MnL]PF(6)⋅0.5 CH(3)OH is the only member of the series that does not exhibit strong hydrogen bonding. At 100 K two of the four SCO complexes (2 and 4) assemble into 1D hydrogen-bonded chains, which weaken or rupture on warming. The remaining SCO complexes 3, 5 and 6 do not form 1D hydrogen-bonded chains, but instead exhibit discrete hydrogen bonding between cation/counterion, cation/solvent or counterion/solvent and show no significant change on warming.