Chemical reduction of π-expanded functionalized pentacene: cooperation of side group in alkali metal binding.

Chemical reduction of a vertically expanded pentacene, TIPS-peri-pentacenopentacene (TIPS-PPP), with sodium metal in THF readily afforded a doubly-reduced product isolated as [{Na+(THF)3}2(TIPS-PPP2-)]. Single-crystal X-ray diffraction revealed the formation of a π-complex of TIPS-PPP2- with two {Na+(THF)3} moieties. The sodium ion is coordinated to three C-atoms at the most negatively charged edge sites and at the lateral ethynyl group. The delocalisation of the charge on the ethynyl function is accompanied by its notable elongation (Δ = 0.015 Å) coupled with the contraction of the adjacent single C-C bond (Δ = 0.033 Å). Bond length analysis supported by Harmonic Aromaticity Oscillator Model (HOMA) shows that the dianion can be written with four aromatic sextets in agreement with the Clar representation. Although TIPS-PPP2- has 36 π-electrons (4n), it does not show a global magnetic paratropic response. The rings with the most negative charge density have a very low paratropic response, while the other rings have a low diatropic response. Overall, the dianion is a non-aromatic molecule.

Synthesis, Aromaticity, and Application of peri-Pentacenopentacene: Localized Representation of Benzenoid Aromatic Compounds.

We report the synthesis and optoelectronic properties of TIPS-peri-pentacenopentacene (TIPS-PPP), a vertical extension of TIPS-pentacene (TIPS-PEN) and a low-band-gap material with remarkable stability. We found the synthetic conditions to avoid the competition between 1,2- and 1,4-addition of lithium acetylide on the large aromatic dione. The high stability of TIPS-PPP is due to the peri-fusion which increases the aromaticity by generating two localized aromatic sextets that are flanked with 2 diene fragments, similar to two fused-anthracenes. Like TIPS-PEN, TIPS-PPP shows the archetypal 2D brickwall motif in crystals with a larger transfer integral and smaller reorganization energy. The high mobility of up to 1 cm2 V-1 s-1 was obtained in an organic field-effect transistor fabricated by a wet process. Also, TIPS-PPP was used as a near-infrared (NIR) emitter for NIR organic-light-emitting-diode devices resulting in a high external quantum efficiency at 800 nm.

Synthesis and photochromic behaviour of a series of benzopyrans bearing an N-phenyl-carbazole moiety: photochromism control by the steric effect.

Five new N-phenyl-carbazole benzopyrans bearing different substitutions on one of the phenyl rings at the sp3 carbon have been synthesized. Their molecular structures were investigated by X-ray and NMR analyses and through quantum chemical calculations. The photochromic mechanism under UV irradiation in toluene, consisting of the consecutive formation of transoid-cis (TC) and transoid-trans (TT) isomers, was studied by UV-vis spectral and kinetic analyses. These molecules have been specifically designed to ascertain the possibility of favouring the formation of the less thermodynamically stable TT at the photostationary state, upon exploiting steric hindrance effects on the diene part of the molecule. The spectrokinetic study allowed the estimation of most of the spectrokinetic parameters, such as molar extinction coefficients, quantum yields of UV colouration and visible photobleaching, and the rate constants of the fast and slow thermal bleaching processes. Peculiar effects of substituents with different donor strengths on one phenyl ring located at the 3-position were observed on the spectrokinetic properties.

Large-scale patterning of π-conjugated materials by meniscus guided coating methods.

Printed organic electronics has attracted considerable interest in recent years as it enables the fabrication of large-scale, low-cost electronic devices, and thus offers significant possibilities in terms of developing new applications in various fields. Easy processing is a prerequisite for the development of low-cost, flexible and printed plastics electronics. Among processing techniques, meniscus guided coating methods are considered simple, efficient, and low-cost methods to fabricate electronic devices in industry. One of the major challenges is the control of thin film morphology, molecular orientations and directional alignment of polymer films during coating processes. Herein, the recent progress of emerging field of meniscus guided printing organic semiconductor materials is discussed. The first part of this report briefly summarizes recent advances in meniscus guided coating techniques. The second part discusses periodic deposits and patterned deposition at moving contact lines, where the mass-transport influences film morphology due to convection at the triple contact line. The last section summarizes our strategy to fabricate large-scale patterning of π-conjugated polymers using meniscus guided method.

Modulating the ground state, stability and charge transport in OFETs of biradicaloid hexahydro-diindenopyrene derivatives and a proposed method to estimate the biradical character.

Biradicaloid compounds with an open-shell ground state have been the subject of intense research in the past decade. Although diindenoacenes are one of the most developed families, only a few examples have been reported as active layers in organic field-effect transistors (OFETs) with a charge mobility of around 10-3 cm2 V-1 s-1 due to a steric disadvantage of the mesityl group to kinetically stabilize compounds. Herein, we disclose our efforts to improve the charge transport of the diindenoacene family based on hexahydro-diindenopyrene (HDIP) derivatives with different annelation modes for which the most reactive position has been functionalized with (triisopropylsilyl)ethynyl (TIPS) groups. All the HDIP derivatives show remarkably higher stability than that of TIPS-pentacene, enduring for 2 days to more than 30 days, which depends on the oxidation potential, the contribution of the singlet biradical form in the ground state and the annelation mode. The annelation mode affects not only the band gap and the biradical character (y 0) but also the value of the singlet-triplet energy gap (ΔE S-T) that does not follow the reverse trend of y 0. A method based on comparison between experimental and theoretical bond lengths has been disclosed to estimate y 0 and shows that y 0 computed at the projected unrestricted Hartree-Fock (PUHF) level is the most relevant among those reported by all other methods. Thanks to their high stability, thin-film OFETs were successfully fabricated. Well balanced ambipolar transport was obtained in the order of 10-3 cm2 V-1 s-1 in the bottom-gate/top-contact configuration, and unipolar transport in the top-gate/bottom-contact configuration was obtained in the order of 10-1 cm2 V-1 s-1 which is the highest value obtained for biradical compounds with a diindenoacene skeleton.

Excellent Semiconductors Based on Tetracenotetracene and Pentacenopentacene: From Stable Closed-Shell to Singlet Open-Shell.

Designing stable open-shell organic materials through the modifications of the π-topology of molecular organic semiconductors has recently attracted considerable attention. However, their uses as an active layer in organic field-effect transistors (OFETs) are very limited, and the obtained hole and electron charge mobilities are around 10-3 cm2 V-1 s-1. Herein, we disclose the synthesis of two peri-fused materials, so-called tetracenotetracene (TT) and pentacenopentacene (PP), which have low band gaps of 1.79 and 1.42 eV, respectively. Their ground state natures have been investigated by different experiments including steady state absorption, electron spin resonance, superconducting quantum interfering device, and variable-temperature NMR along with DFT calculations. TT and PP have closed-shell and singlet open-shell structures in their ground state, respectively, and possess high stability. Their biradical characteristics were found to be 0.50 and 0.64. The origin of the open-shell character of PP is related to the concomitant opening of two tetracenes with the recovering of two extra aromatic sextets and a small HOMO-LUMO energy gap (gap <1.5 eV). Thanks to the high stability, thin film OFET devices could be fabricated. In TG-BC configuration PP shows a remarkably high hole mobility of 1.4 cm2 V-1 s-1, while TT exhibits a hole mobility of 0.77 cm2 V-1 s-1. In the configuration of BG-TC, ambipolar behaviors for both were obtained with hole and electron mobilities of 0.21 and 0.01 cm2 V-1 s-1 for PP and 0.14 and 0.006 cm2 V-1 s-1 for TT.

Serendipitous Rediscovery of the Facile Cyclization of Z,Z-3,5-Octadiene-1,7-diyne Derivatives to Afford Stable, Substituted Naphthocyclobutadienes.

The serendipitous isolation of very small amounts of two naphthocyclobutadiene (NCB) derivatives has led to the computational re-examination of the electrocyclization of Z,Z-3,5-octadiene-1,7-diyne as well as the experimental and computational study of diethynylindeno[2,1-a]fluorene derivatives that contain the 3,5-octadiene-1,7-diyne motif as part of a larger π-framework. In both cases the calculated potential energy surface strongly implicates two successive electrocyclic reactions to afford the antiaromatic products. With the octadienediyne fragment locked in the reactive conformation, the postulated diethynylindeno[2,1-a]fluorene intermediates afford the NCBs in modest to good yields. X-ray crystallography of four NCBs as well as NICS-XY scan calculations show that the paratropic motif is located primarily in the benzocyclobutadiene fragment within the larger π-scaffold.

Synthesis and Properties of Benzo-Fused Indeno[2,1-c]fluorenes.

A set of fully-conjugated indenofluorenes has been synthesized and confirmed by solid-state structure analysis. The indeno[2,1-c]fluorenes and their benzo-fused analogues all contain the antiaromatic as-indacene core. The molecules possess high electron affinities and show a broad absorption that reaches into the near-IR region of the electromagnetic spectrum. All of the featured compounds reversibly accept up to two electrons as revealed by cyclic voltammetry. Analysis of molecule tropicity using NICS-XY scan calculations shows that, while the as-indacene core is less paratropic than s-indacene, benz[a]-annulation further reduces the antiaromaticity of the core. Antiaromatic strength of the as-indacene core can also be tuned by the position of fusion of additional arenes on the outer rings.

Chiral separation of helical chromenes with chloromethyl phenylcarbamate polysaccharide-based stationary phases.

Two chloromethyl phenylcarbamate-based chiral stationary phases, one containing an amylose-type chiral selector (Lux Amylose 2, from Phenomenex) and the other a cellulose-type one (Lux Cellulose-4, from Phenomenex), were successfully used for the chiral resolution of three helical chromenes featuring a helicene-like structure. The compound bearing a phenyl substituent on the helicene-like structure was enantioresolved at 25°C with Lux Cellulose-4 and a n-hexane/1-propanol 99:1 v/v eluent. With a n-hexane/2-propanol 99.8:0.2 v/v mobile phase, the same column (operated at 35°C) provided the separation of the four isomers of the compound having a hexyl residue on the helicene-like motif and an additional asymmetric carbon. Lux Amylose-2 was necessary for the enantioseparation of the compound having the sole hexyl residue on the helical scaffold. For the last compound a n-hexane/2-propanol 99.8:0.2 v/v eluent was used, and the column temperature was fixed at 5°C. The enantiomer elution order was appraised by using electronic circular dichroism and theoretical calculations. Notably, different thermodynamics of retention and enantioseparation were observed for molecules with pronounced structural similarity, that is, the enantiomer pairs of the compound containing the additional asymmetric carbon atom. Indeed, both entropically and enthalpically controlled adsorption and separation processes were observed.

Novel Fluorophores based on Regioselective Intramolecular Friedel-Crafts Acylation of the Pyrene Ring Using Triflic Acid.

The extension of the pyrene ring from dimethyl 2,2'-(pyrene-1,6-diyl)dibenzoate derivatives by an intramolecular Friedel-Crafts acylation can be realized in an efficient and regioselective manner using triflic acid as proton source. Naphtho-tetracenone derivatives are obtained in high yields at room temperature while Bis-tetracene-diones are prepared upon heating. Both products display interesting fluorescence properties in the visible range with quantum yields varying from 50 to 60 %.

Low Bandgap Bistetracene-Based Organic Semiconductors Exhibiting Air Stability, High Aromaticity and Mobility.

The benchmark of soluble organic semiconductors based on acenes is the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-PEN). However TIPS-PEN still suffers from photoinduced oxidation due to its low degree of aromaticity. Increasing the aromaticity while keeping similar optical and electrochemical properties as well as a shape suitable for good hole transport can be achieved with two-dimensional polycyclic aromatic hydrocarbons (2D-PAHs). Herein, we present an efficient synthesis and characterization of bistetracene derivatives that exhibit a band gap up to 1.71 eV and an increased stability up to 21 times compared to TIPS-PEN and mobility over 0.1 cm2 V-1 s-1 in solution-processed organic field-effect transistors. Based on simple structural consideration, the high stability is attributed to the aromaticity of the bistetracene which is comparable to an anthrancene along each tetracene. According to Clar's sextet rule, the bistetracene should be best regarded as two anthracenes fused at the face bridged by two ethylenic spacers. The synthesis path paves the way towards the preparation of ambipolar and/or longer 2D-PAHs such as bispentacenes and could give rise to organic semiconductors with interesting properties.

Tetraceno[2,1,12,11-opqra]tetracene-extended tetrathiafulvalene - redox-controlled generation of a large PAH core.

Two tetraceno[2,1,12,11-opqra]tetracene-extended tetrathia-fulvalenes were prepared and found to undergo reversible conversion into their planar polycyclic aromatic hydrocarbons (PAHs) upon electrochemical oxidation - at potentials probing the best valence bond representations.

A helical naphthopyran dopant for photoresponsive cholesteric liquid crystals.

The first photoresponsive cholesteric liquid crystal comprising a photoisomerizable helical naphthopyran derivative dopant and a nematic liquid crystal is reported. An unprecedented helical twisting power switching ratio of over 90% allowed us to demonstrate multi-cycle rotational motion of micro-objects by UV light irradiation.

Unraveling Triplet Excitons Photophysics in Hyper-Cross-Linked Polymeric Nanoparticles: Toward the Next Generation of Solid-State Upconverting Materials.

The technological application of sensitized upconversion based on triplet-triplet annihilation (TTA) requires the transition from systems operating in liquid solutions to solid-state materials. Here, we demonstrate that the high upconversion efficiency reported in hyper-cross-linked nanoparticles does not originate from residual mobility of the embedded dyes as it happens in soft hosts. The hyper-reticulation from one side blocks the dyes in fixed positions, but on the other one, it suppresses the nonradiative spontaneous decay of the triplet excitons, reducing intramolecular relaxations. TTA is thus enabled by an unprecedented extension of the triplet lifetime, which grants long excitons diffusion lengths by hopping among the dye framework and gives rise to high upconversion yield without any molecular displacement. This finding paves the way for the design of a new class of upconverting materials, which in principle can operate at excitation intensities even lower than those requested in liquid or in rubber hosts.

P-Type Photochromism of New Helical Naphthopyrans: Synthesis and Photochemical, Photophysical and Theoretical Study.

Two novel helical naphthopyrans have been synthesised. The helical scaffold has the interesting effect of increasing the thermal stability of the transoid-trans (TT) open isomer formed upon UV irradiation of the closed form (CF), which transforms these naphthopyrans from thermal to photochemical photochromes. The photochromic performance is excellent in both polar and apolar solvents and the conversion percentage from the CF to the TT form can be as high as 92.8 %. We propose a new method to determine the quantum yields of the photochemical processes that lead to transoid-cis (TC) and TT isomers, and their molar absorption coefficients. The thermal stability of the TT and TC isomers has been studied in different solvents. The quantum yields of fluorescence before and after irradiation, along with the decay lifetimes, have also been measured. TD-DFT calculations have been performed to determine the relative thermodynamic stability of the species involved in the photochromic mechanism and to rationalise their spectral properties.

Diindeno[1,2-b:2',1'-n]perylene: a closed shell related Chichibabin's hydrocarbon, the synthesis, molecular packing, electronic and charge transport properties.

Diindeno[1,2-b:2',1'-n]perylene, a new derivative of the indenoacene family was synthesized, and its electronic, electrochemical, and electrical properties were investigated. This material has a closed shell electronic configuration which corresponds to a quinoidal structure with a low band gap of 1.35 eV. Molecular packing in the single crystal was studied by single-crystal X-ray structural analysis, and this information was subsequently used in the determination of the charge transfer integrals via density functional theory methods. The charge-carrier transport properties of the diindeno[1,2-b:2',1'-n]perylene-5,12-dione and diindeno[1,2-b:2',1'-n]perylene derivatives were investigated through the fabrication and characterization of field-effect transistors via both vacuum-deposited and solution-processed films, respectively. Diindeno[1,2-b:2',1'-n]perylene exhibited a field-effect behaviour with a hole mobility up to 1.7 × 10-3 cm2 V-1 s-1 when the active layer was solution-processed.

A lithium-organic framework with coordinatively unsaturated metal sites that reversibly binds water.

The synthesis and characterisation of a three-dimensional lithium-organic framework MIL-145 is described, which upon thermal treatment yields a second open framework, MIL-146, that contains four and three-coordinate lithium centres: the coordinatively unsaturated trigonal planar lithium centres are able to reversibly bind water with crystallinity maintained, while the dehydrated phase shows preferential adsorption of CO(2) over N(2).

The control of photochromism of [3H]-naphthopyran derivatives with intramolecular CH-π bonds.

The photochromism of [3H]-naphthopyran derivatives can be switched from T-type to inverse- or P-type through the manipulation of relative thermodynamic stabilities of open isomers with intramolecular CH-π bonds.

Photoswitching of bis-spiropyran using near-infrared excited upconverting nanoparticles.

Bis-spiropryran molecules were grafted onto the surface of upconverting nanoparticles. Fluorescence resonance energy transfer from the upconverting nanoparticles to the surface bis-spiropyran molecules triggered the transformation of the ring-closed bis-spiropyran to the ring-open bis-merocyanine forms.

Light-driven directed motion of azobenzene-coated polymer nanoparticles in an aqueous medium.

Azobenzene-coated polymer nanoparticles in the 16-nm-diameter range act as phototriggered nanomotors combining photo to kinetic energy conversion with optical control through light intensity gradients. The grafted dyes act as molecular propellers: their photoisomerization supplies sufficient mechanical work to propel the particles in an aqueous medium toward the intensity minima with velocities of up to 15 µm/s. It is shown that nanoparticles can be driven over tens of micrometers by translating the intensity gradients in the plane. The analysis of the particles motion demonstrates the decisive role of photoisomerization in the transport with a measured driving force that is 3 to 4 orders of magnitude higher than optical forces.