Dense layers of semiconducting single-walled carbon nanotubes (SWNTs) serve as electrochromic (EC) materials in the near-infrared with high optical density and high conductivity. EC cells with tunable notch filter properties instead of broadband absorption are created via highly selective dispersion of specific semiconducting SWNTs through polymer-wrapping followed by deposition of thick films by aerosol-jet printing. A simple planar geometry with spray-coated mixed SWNTs as the counter electrode renders transparent metal oxides redundant and facilitates complete bleaching within a few seconds through iongel electrolytes with high ionic conductivities. Monochiral (6,5) SWNT films as working electrodes exhibit a narrow absorption band at 997 nm (full width at half-maximum of 55–73 nm) with voltage-dependent optical densities between 0.2 and 4.5 and a modulation depth of up to 43 dB. These (6,5) SWNT notch filters can retain more than 95% of maximum bleaching for several hours under open-circuit conditions. In addition, different levels of transmission can be set by applying constant low voltage (1.5 V) pulses with modulated width or by a given number of fixed short pulses.

Reaction of the pseudotetrahedral tetracarboxylic acid proligand tetrakis(4-carboxyphenyl)silane (H4L) with salts of various lanthanoid metals has afforded three new lanthanoid coordination polymers: {[H3O]2[Ce2(L)2(H2O)2]·2DMF·2H2O}∞ (1), {[Eu3L2(NO3)(DMF)4(H2O)]·0.5DMF·6H2O}∞ (2), and {Eu(HL)(DMF)2(H2O)]·DMF·2.5H2O}∞ (3) (DMF = N,N′-dimethylformamide), which have been structurally characterized by single-crystal X-ray diffraction. Compounds 1 and 2 are both noninterpenetrated three-dimensional networks that display the rare fluorite (CaF2) topology. In compound 1, the fully deprotonated L4– ligands act as pseudotetrahedral 4-connecting nodes and dinuclear cerium-carboxylate building blocks act as 8-connecting nodes, while in compound 2 the L4– ligands and trinuclear europium-carboxylate units are 4- and 8-connecting, respectively. In contrast, compound 3 exhibits a two-dimensional layered structure with triply deprotonated HL3– ligands acting as 3-connecting units, linking single europium centers within each layer. Gas sorption studies of 2 show a high affinity of the pretreated microcrystalline solid for carbon dioxide gas.

The new coordination polymer [ε-PMo 12 O 37 (OH) 3 {La-(H 2 O) 3 } 4 (L)]·28H 2 O [H 4 L = tetrakis(4-carboxyphenyl)silane] can be synthesized by combining equal quantities of two types of 4-connecting building blocks: organic L 4ligands and inorganic polyoxometalate-derived [ε-PMo 12 O 37 (OH) 3 -[a]

The guanidino-functionalized aromatic compound 1,2,4,5-tetrakis(tetramethylguanidino)benzene (ttmgb) has been shown to be an efficient n-dopant for field-effect transistors (FETs) with gold contacts and networks of semiconducting single-walled carbon nanotubes (SWCNTs) with small diameters and large band gaps. Here, we investigate the broader applicability of ttmgb as a molecular n-dopant by fabricating bottom-contact/top-gate FETs with different air-stable, high work function metals as electrodes and with both small-and large-diameter polymer-sorted SWCNTs. Kelvin probe measurements indicate a reduction of the work functions of gold, palladium, and platinum by about 1 eV after ttmgb treatment and, correspondingly, gated four-point probe measurements show orders of magnitude lower contact resistances for electron injection into SWCNT networks. FETs based on networks of (6,5) SWCNTs with large band gaps as well as mixed semiconducting plasma torch SWCNTs with small band gaps can thus be transformed from ambipolar to purely n-type with no hole injection or increased off-currents by applying optimized ttmgb concentrations. Carrier concentration-and temperature-dependent measurements reveal that ttmgb treatment does not impact the electron transport and maximum mobilities in SWCNT networks at high carrier densities, but greatly improves the subthreshold slope of nanotube FETs by removing shallow electron trap states. This effect is found to be particularly pronounced for small-diameter nanotubes with large band gaps.

Trions are charged excitons that form upon optical or electrical excitation of low-dimensional semiconductors in the presence of charge carriers (holes or electrons). Trion emission from semiconducting single-walled carbon nanotubes (SWCNTs) occurs in the near-infrared and at lower energies compared to the respective exciton. It can be used as an indicator for the presence of excess charge carriers in SWCNT samples and devices. Both excitons and trions are highly sensitive to the surrounding dielectric medium of the nanotubes, having an impact on their application in optoelectronic devices. Here, the influence of different dielectric materials on exciton and trion emission from electrostatically doped networks of polymersorted (6,5) SWCNTs in top-gate field-effect transistors is investigated. The observed differences of trion and exciton emission energies and intensities for hole and electron accumulation cannot be explained with the polarizability or screening characteristics of the different dielectric materials, but they show a clear dependence on the charge trapping properties of the dielectrics. Charge localization (trapping of holes or electrons by the dielectric) reduces exciton quenching, emission blue-shift and trion formation. Based on the observed carrier type and dielectric material dependent variations, the ratio of trion to exciton emission and the exciton blue-shift are not suitable as quantitative metrics for doping levels of carbon nanotubes.

The application of n-dopants in organic field-effect transistors (FETs) enables improvement of electron injection and transport.

The back cover picture shows the aqueous assembly of a new coordination polymer from 4‐connecting inorganic and organic building blocks. The coordination polymer exhibits a diamondoid topology in which the lanthanide‐functionalized polyoxometalate and tetracarboxylate building blocks act as pseudotetrahedral nodes. Details are discussed in the article by C. Ritchie, C. Boskovic et al. on p. 1631 ff. Stuffpoint.com is acknowledged for supplying the background graphic.