Functional Molecular Materials Research Articles

Solution-processed molecular functional materials for organic optoelectronics

Solution-processed molecular functional materials for organic optoelectronics

ChemInform Abstract: Photoisomerization in Different Classes of Azobenzene

AbstractReview: 261 refs.

ChemInform Abstract: Playing with Organic Radicals as Building Blocks for Functional Molecular Materials

AbstractReview: 257 refs.

Dynamics of Molecular Rotors Confined in Two Dimensions: Transition from a 2D Rotational Glass to a 2D Rotational Fluid in a Periodic Mesoporous Organosilica

The motional behavior of p-phenylene-d(4) rotators confined within the 2D layers of a hierarchically ordered periodic mesoporous p-divinylbenzenesilica has been elucidated to evaluate the effects of reduced dimensionality on the engineered dynamics of artificial molecular machines. The hybrid mesoporous material, characterized by a honeycomb lattice structure, has arrays of alternating p-divinylbenzene rotors and siloxane layers forming the molecularly ordered walls of the mesoscopic channels. The p-divinylbenzene rotors are strongly anchored between two adjacent siloxane sheets, so that the p-phenylene rotators are unable to experience translational diffusion and are allowed to rotate about only one fixed axis. Variable-temperature (2)H NMR experiments revealed that the p-phenylene rotators undergo an exchange process between sites related by 180° and a non-Arrhenius temperature dependence of the dynamics, with reorientational rates ranging from 10(3) to 10(8) Hz between 215 to 305 K. The regime of motion changes rapidly at about 280 K indicating the occurrence of a dynamical transition. The transition was also recognized by a steep change in the heat capacity at constant pressure. As a result of the robust lamellar architecture comprising the pore walls, the orientational dynamic disorder related to the phase transition is only realized in two dimensions within the layers, that is in the plane perpendicular to the channel axis. Thus, the aligned rotors that form the organic layers exhibit unique anisotropic dynamical properties as a result of the architecture's reduced dimensionality. The dynamical disorder restricted to two dimensions constitutes a highly mobile fluidlike rotational phase at room temperature, which upon cooling undergoes a transition to a more rigid glasslike phase. Activation energies of 5.9 and 9.5 kcal/mol respectively have been measured for the two dynamical regimes of rotation. Collectively, our investigation has led to the discovery of an orientationally disordered 2D rotational glass and its transition from rigid to soft at increasing temperature. The spectral narrowing observed in the (2)H NMR experiments at higher temperatures (310-420 K) is consistent with fast rotational dynamics, which remain anisotropic in nature within the robust lamellar architecture. This study suggests that exploiting reduced dimensionality in the design of solid-state artificial molecular machines and functional materials may yield access to behavior previously unrealized in 3D materials.

ChemInform Abstract: Wraparound Hosts for Fullerenes: Tailored Macrocycles and Cages

AbstractReview: about 100 refs.

What makes efficient circularly polarised luminescence in the condensed phase: aggregation-induced circular dichroism and light emission

In this contribution, we conceptually present a new avenue to construction of molecular functional materials with high performance of circularly polarised luminescence (CPL) in the condensed phase. A molecule (1) containing luminogenic silole and chiral sugar moieties was synthesized and thoroughly characterized. In a solution of 1, no circular dichroism (CD) and fluorescence emission are observed, but upon molecular aggregation, both the CD and fluorescence are simultaneously turned on, showing aggregation-induced CD (AICD) and emission (AIE) effects. The AICD effect is supported by the fact that the molecules readily assemble into right-handed helical nanoribbons and superhelical ropes when aggregated. The AIE effect boosts the fluorescence quantum efficiency (ΦF) by 136 fold (ΦF, ∼0.6% in the solution versus ∼81.3% in the solid state), which surmounts the serious limitations of aggregation-caused quenching effect encountered by conventional luminescent materials. Time-resolved fluorescence study and theoretical calculation from first principles conclude that restriction of the low-frequency intramolecular motions is responsible for the AIE effect. The helical assemblies of 1 prefer to emit right-handed circularly polarised light and display large CPL dissymmetry factors (gem), whose absolute values are in the range of 0.08–0.32 and are two orders of magnitude higher than those of commonly reported organic materials. We demonstrate for the first time the use of a Teflon-based microfluidic technique for fabrication of the fluorescent pattern. This shows the highest gem of −0.32 possibly due to the enhanced assembling order in the confined microchannel environment. The CPL performance was preserved after more than half year storage under ambient conditions, revealing the excellent spectral stability. Computational simulation was performed to interpret how the molecules in the aggregates interact with each other at the molecular level. Our designed molecule represents the desired molecular functional material for generating efficient CPL in the solid state, and the current study shows the best results among the reported organic conjugated molecular systems in terms of emission efficiency, dissymmetry factor, and spectral stability.

Photoisomerization in different classes of azobenzene

Azobenzene undergoes trans→cis isomerization when irradiated with light tuned to an appropriate wavelength. The reverse cis→trans isomerization can be driven by light or occurs thermally in the dark. Azobenzene's photochromatic properties make it an ideal component of numerous molecular devices and functional materials. Despite the abundance of application-driven research, azobenzene photochemistry and the isomerization mechanism remain topics of investigation. Additional substituents on the azobenzene ring system change the spectroscopic properties and isomerization mechanism. This critical review details the studies completed to date on the 3 main classes of azobenzene derivatives. Understanding the differences in photochemistry, which originate from substitution, is imperative in exploiting azobenzene in the desired applications.

1,1’-Bis(diphenylphosphino)ferrocene in functional molecular materials

The bidentate ligand 1,1'-bis(diphenylphosphino)ferrocene (dppf) is a widely used component in catalytic systems and its role in this capacity has been expertly reviewed elsewhere. The focus of this Perspective is the increasing use of dppf in the synthesis and matrix of 21st century materials. The ferrocene core imparts fine control to catalytic C-C and C-X coupling reactions used to manufacture a range of functional macromolecules from tailored dyes and OLED components to precisely engineered conducting polymers and thermoplastics. This ligand's limited flexibility resembles a ball and socket joint with simultaneous rotation and constrained perpendicular freedom. This uniquely restricted range of movement stabilizes a diverse array of ground and transition states for these important transition metal catalysed coupling reactions. It may also contribute desirable mechanical or electronic functionality as a bridging or chelating component in a coordination array, metallocycle or larger supramolecular assembly. The ferrocene offers steric bulk and crystallinity to these materials aiding chemical stability and ease of handing. It's oxidizability assists characterization and may be tailored to provide or complement photo- or electroactivity. Dppf containing materials have been designed with diverse functions from cooperative luminescence to host-guest complexation. It is likely that this ubiquitous lab companion will increasingly find its way into the fabric or processing of future functional molecular materials.

Playing with organic radicals as building blocks for functional molecular materials

The literature has shown numerous contributions on the synthesis and physicochemical properties of persistent organic radicals but there are a lesser number of reports about their use as building blocks for obtaining molecular magnetic materials exhibiting an additional and useful physical property or function. These materials show promise for applications in spintronics as well as bistable memory devices and sensing materials. This critical review provides an up-to-date survey to this new generation of multifunctional magnetic materials. For this, a detailed revision of the most common families of persistent organic radicals-nitroxide, triphenylmethyl, verdazyl, phenalenyl, and dithiadiazolyl-so far reported will be presented, classified into three different sections: materials with magnetic, conducting and optical properties. An additional section reporting switchable materials based on these radicals is presented (257 references).

Wraparound Hosts for Fullerenes: Tailored Macrocycles and Cages

Custom-made macrocyclic receptors for fullerenes are proving a valuable alternative to achieve the affinity and selectivity required to meet challenges such as the selective extraction of higher fullerenes, their chiral resolution, or the self-assembly of functional molecular materials. In this Minireview, we highlight some of the important breakthroughs that this class of fullerene hosts has already produced.

Ultra-fast Rotors for Molecular Machines and Functional Materials via Halogen Bonding: Crystals of 1,4-Bis(iodoethynyl)bicyclo[2.2.2]octane with Distinct Gigahertz Rotation at Two Sites

Ultra-fast Rotors for Molecular Machines and Functional Materials via Halogen Bonding: Crystals of 1,4-Bis(iodoethynyl)bicyclo[2.2.2]octane with Distinct Gigahertz Rotation at Two Sites

Supramolecular Bola-Like Ferroelectric: 4-Methoxyanilinium Tetrafluoroborate-18-crown-6

Molecular motion is one of the structural foundations for the development of functional molecular materials such as artificial motors and molecular ferroelectrics. Herein, we show that pendulum-like motion of the terminal group of a molecule causes a ferroelectric phase transition. Complex 4-methoxyanilinium tetrafluoroborate-18-crown-6 ([C(7)H(10)NO(18-crown-6)](+)[BF(4)](-), 1) shows a second-order ferroelectric phase transition at 127 K, together with an abrupt dielectric anomaly, Debye-type relaxation behavior, and the symmetry breaking confirmed by temperature dependence of second harmonic generation effect. The origin of the polarization is due to the order-disorder transition of the pendulum-like motions of the terminal para-methyl group of the 4-methoxyanilinium guest cation; that is, the freezing of pendulum motion at low temperature forces significant orientational motions of the guest molecules and thus induces the formation of the ferroelectric phase. The supramolecular bola-like ferroelectric is distinct from the precedent ferroelectrics and will open a new avenue for the design of polar functional materials.

Discrete Covalent Organic–Inorganic Hybrids: Terpyridine Functionalized Polyoxometalates Obtained by a Modular Strategy and Their Metal Complexation

The rational design and synthesis of organic-inorganic hybrids as functional molecular materials relies on both the careful conception of building-blocks and the strategy for their assembly. Three families of trialkoxo polyoxometalates (Lindqvist 2, Anderson 3, Dawson 4) grafted with remote terpyridine coordination sites have been synthesized to extend the available building-blocks. These new units can be combined with metal complexes that play a role as (i) chromophores toward charge-separated systems in light-harvesting devices and (ii) coordination motifs for metal-directed self-assembly toward multifunctional molecular hybrid materials. The X-ray crystal structures of polyoxometalate-terpyridine hybrids indicate distances of 21 Å and 19 Å between the two terpyridyl coordination sites in 2 and 3, respectively, with angles between the coordination vectors of 180° and 177.4°, respectively. Lindqvist 2 displays a reduction at -0.52 V vs SCE while Anderson 3 exhibits one reversible oxidation attributed to Mn(III)/Mn(IV) (+0.75 V vs SCE) and a broad wave at -1.28 V vs SCE assigned to the Mn(III)/Mn(II) reduction. Dawson 4 displays several processes on a wide range of potentials (+0.5 to -2.0 V vs SCE) centered on V(V), W(VI) and the organic ligand in order of decreasing potentials. The grafted terpyridine ligands in Anderson 3 and Dawson 4 were successfully coordinated to {PdCl}(+) and {RuCl(3)} moieties, respectively. The polyoxometalates and transition metal complexes retain their intrinsic properties in the final assemblies.

Ultra-fast Rotors for Molecular Machines and Functional Materials via Halogen Bonding: Crystals of 1,4-Bis(iodoethynyl)bicyclo[2.2.2]octane with Distinct Gigahertz Rotation at Two Sites

As a point of entry to investigate the potential of halogen-bonding interactions in the construction of functional materials and crystalline molecular machines, samples of 1,4-bis(iodoethynyl)bicyclo[2.2.2]octane (BIBCO) were synthesized and crystallized. Knowing that halogen-bonding interactions are common between electron-rich acetylenic carbons and electron-deficient iodines, it was expected that the BIBCO rotors would be an ideal platform to investigate the formation of a crystalline array of molecular rotors. Variable temperature single crystal X-ray crystallography established the presence of a halogen-bonded network, characterized by lamellarly ordered layers of crystallographically unique BIBCO rotors, which undergo a reversible monoclinic-to-triclinic phase transition at 110 K. In order to elucidate the rotational frequencies and the activation parameters of the BIBCO molecular rotors, variable-temperature (1)H wide-line and (13)C cross-polarization/magic-angle spinning solid-state NMR experiments were performed at temperatures between 27 and 290 K. Analysis of the (1)H spin-lattice relaxation and second moment as a function of temperature revealed two dynamic processes simultaneously present over the entire temperature range studied, with temperature-dependent rotational rates of k(rot) = 5.21 × 10(10) s(-1)·exp(-1.48 kcal·mol(-1)/RT) and k(rot) = 8.00 × 10(10) s(-1)·exp(-2.75 kcal·mol(-1)/RT). Impressively, these correspond to room temperature rotational rates of 4.3 and 0.8 GHz, respectively. Notably, the high-temperature plastic crystalline phase I of bicyclo[2.2.2]octane has a reported activation energy of 1.84 kcal·mol(-1) for rotation about the 1,4 axis, which is 24% larger than E(a) = 1.48 kcal·mol(-1) for the same rotational motion of the fastest BIBCO rotor; yet, the BIBCO rotor has three fewer degrees of translational freedom and two fewer degrees of rotational freedom! Even more so, these rates represent some of the fastest engineered molecular machines, to date. The results of this study highlight the potential of halogen bonding as a valuable construction tool for the design and the synthesis of amphidynamic artificial molecular machines and suggest the potential of modulating properties that depend on the dielectric behavior of crystalline media.

Selective synthesis of poly-substituted fluorine-containing pyridines and dihydropyrimidines via cascade C–F bond cleavage protocol

Fluorinated azaheterocycles are frequently found in pharmaceuticals, drug candidates, ligands for transition metal catalysts, and other molecular functional materials, so efficient methods for the synthesis of these compounds are of significant value. We herein describe a selective strategy for the synthesis of poly-substituted pyridines and fluoroalkyl dihydropyrimidines based on C-F bond breaking of the anionically activated fluoroalkyl group. An array of pyridines and dihydropyrimidines were prepared through this domino process in high yields under noble metal catalyst-free conditions, making this method a valuable supplement to azaheterocycle synthesis.

A dirhodium(ii,ii) complex as a highly selective molecular material for ammonia detection: QCM studies

The well known axial coordination capabilities of dirhodium(II,II) complexes towards Lewis bases have been exploited for the development of functional molecular materials for selective ammonia monitoring. On the basis of literature data and experimental evidence, the [Rh2(form)4] (1) (form = N,N′-di-p-tolylformamidinate anion) complex has been selected, among a series of dirhodium(II,II) derivatives, as the most suitable for this aim. By exposure to gaseous ammonia, 1 readily reacts, both in solution and in the solid state, with the gas to afford the corresponding ammonia-axial adduct. The reaction is reversible and is accompanied by a significant color change from dark yellow-green to red-brown due to the adduct formation, as confirmed by RGB, UV-vis and FT-IR spectroscopic investigations. Solid state UV/vis spectra reveal that while ammonia coordination occurs steadily, as judged by the blue shift observed for the λmax (470 for 1vs. 430 nm for the adduct), its complete release, in free air, takes more than a week. The potentiality of 1 for the selective ammonia detection in the headspace of aqueous ammonia solutions has been examined by QCM investigations. The dynamic response obtained from such studies is consistent with a reversible binding process occurring at the layer surface, which is operating once a fraction of the analyte is “irreversibly” bound to the sensor layer. The QCM response shows an excellent linearity in a wide concentration range (1–30 wt%) without any saturation effect up to high ammonia levels and a high selectivity to ammonia among a wide range of interfering gases.

New progress in aggregation-induced emission research

The most fascinating aspect of scientific research is the constant deciphering of mysterious puzzles and the continuous transformation of our mode of thinking. While textbook knowledge is the foundation of human wisdom, some traditional concepts can later prove to be imperfect or even incorrect owing to limitations of the observations and understanding of the involved natural phenomena in particular periods of history. The once popular “geocentric theory”, for example, was totally wrong and hampered scientists’ exploration of the universe, and the “vitality of the doctrine” badly hindered advancement in organic chemistry research. Innovations are needed to break the restraints of such traditional concepts. The area of organic solids research focuses on investigations of molecular functional materials with peculiar optical, electronic and magnetic properties. In this area, a generally accepted concept is that chromophore aggregation always leads to luminescence quenching. This phenomenon of aggregation-caused quenching (ACQ) is termed the “concentration-quenching effect” in the textbook Molecular Fluorescence. Researchers are working on the development of organic light-emitting diodes (OLEDs), in which luminescent molecules are used as a solid film, one of the aggregation forms. Scientists have tried hard to suppress the aggregate formation of luminescent molecules through different approaches, with the aim of mitigating the ACQ effect and achieving OLEDs with high efficiencies. In 2001, Tang’s group discovered a phenomenon exactly opposite to the ACQ effect. The researchers found that luminogen aggregation played a constructive, instead of destructive, role in the light-emitting process; a series of silole molecules, such as hexaphenylsilole (HPS) and methylpentaphenylsilole (MPPS; Figure 1), were found to be nonluminescent in the solution state but emissive in the aggregated state with luminescent quantum yields three orders of

ChemInform Abstract: s‐Tetrazines as Building Blocks for New Functional Molecules and Molecular Materials

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

C-H bonds as ubiquitous functionality: a general approach to complex arylated imidazoles via regioselective sequential arylation of all three C-H bonds and regioselective N-alkylation enabled by SEM-group transposition.

Imidazoles are an important group of the azole family of heterocycles frequently found in pharmaceuticals, drug candidates, ligands for transition metal catalysts, and other molecular functional materials. Owing to their wide application in academia and industry, new methods and strategies for the generation of functionalized imidazole derivatives are in demand. We here describe a general and comprehensive approach for the synthesis of complex aryl imidazoles, where all three C-H bonds of the imidazole core can be arylated in a regioselective and sequential manner. We report new catalytic methods for selective C5- and C2-arylation of SEM-imidazoles and provide a mechanistic hypothesis for the observed positional selectivity based on electronic properties of C-H bonds and the heterocyclic ring. Importantly, aryl bromides and low-cost aryl chlorides can be used as arene donors under practical laboratory conditions. To circumvent the low reactivity of the C-4 position, we developed the SEM-switch that transfers the SEM-group from N-1 to N-3 nitrogen and thus enables preparation of 4-arylimidazoles and sequential C4-C5-arylation of the imidazole core. Furthermore, selective N3-alkylation followed by the SEM-group deprotection (trans-N-alkylation) allows for regioselective N-alkylation of complex imidazoles. The sequential C-arylation enabled by the SEM-switch allowed us to produce a variety of mono-, di-, and triarylimidazoles using diverse bromo- and chloroarenes. Using our approach, the synthesis of individual compounds or libraries of analogues can begin from either the parent imidazole or a substituted imidazole, providing rapid access to complex imidazole structures.

S-Tetrazines as Building Blocks for New Functional Molecules and Molecular Materials

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTs-Tetrazines as Building Blocks for New Functional Molecules and Molecular MaterialsGilles Clavier* and Pierre Audebert*View Author Information PPSM, ENS Cachan, CNRS, UniverSud, 61 av President Wilson, F-94230 Cachan, France* To whom correspondence should be addressed. E-mail: [email protected] (G.C.) and [email protected] (P.A.).Cite this: Chem. Rev. 2010, 110, 6, 3299–3314Publication Date (Web):March 22, 2010Publication History Received4 November 2009Published online22 March 2010Published inissue 9 June 2010https://doi.org/10.1021/cr900357eCopyright © 2010 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views10245Altmetric-Citations299LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (2 MB) Get e-AlertsSUBJECTS:Anions,Fluorescence,Molecules,Redox reactions,Substituents Get e-Alerts