Large Π-conjugated System Research Articles

Assessing long-range corrected functionals with physically-adjusted range-separated parameters for calculating the polarizability and the second hyperpolarizability of polydiacetylene and polybutatriene chains

The use of physically-adjusted range-separated parameter (μ) together with long-range corrected exchange-correlation functionals is shown not to be reliable for calculating the polarizability (α) and the second hyperpolarizability (γ) of large π-conjugated systems. This statement has been substantiated by calculating the polarizability and the second hyperpolarizability of increasingly large polydiacetylene and polybutatriene chains in comparison with reference data evaluated at the coupled-cluster singles and doubles with perturbative estimation of the triples [CCSD(T)] level. Further comparisons highlight that long-range corrected exchange-correlation functionals with conventional and larger range-separated parameters perform better for α (μ = 0.47) and γ (μ = 0.33 and 0.47) but for polybutatriene chains none can describe satisfactorily the chain length evolution of γ. On the other hand, Møller-Plesset second- and fourth-order values are in closer agreement with CCSD(T), except for γ of polybutatriene, which is strongly overestimated.

Transition metal catalyzed borylation of functional π-systems

Borylated functional π-systems are useful building blocks to enable efficient synthesis of novel molecular architectures with beautiful structures, intriguing properties and unique functions. Introduction of boronic ester substituents to a variety of extended π-systems can be achieved through either iridium-catalyzed direct C–H borylation or the two-step procedure via electrophilic halogenation followed by palladium-catalyzed borylation. This review article focuses on our recent progress on borylation of large π-conjugated systems such as porphyrins, perylene bisimides, hexabenzocoronenes and dipyrrins.

Synthesis and photophysical properties of platinum(II) arylacetylides with donor–acceptor structures

The detailed relationship between the structure and the nonlinear mechanisms, as well as whether different nonlinear mechanisms of an organic molecule restrain each other are still not clear. In this paper, eight platinum(II) arylacetylides with donor–acceptor structures were synthesized and their photophysical properties were studied systematically. The properties of HOMO and LUMO were calculated using DFT method, the contribution of the metal dπ and charge transfer process are dominated by the skeleton structure of these complexes. The ligand-to-metal charge transfer (LMCT) happens when the molecule with D–π–Pt–π–D or D–π–Pt–π–Ar–π–Pt–π–D skeleton is excited, however the metal-to-ligand charge transfer (MLCT) and ligand-to-ligand charge transfer (LLCT) happen when the molecule with D–π–Pt–π–A, A–π–Pt–π–A or A–π–Pt–π–Ar–π–Pt–π–A skeleton is excited, respectively. The weak absorption in the visible area of these molecules provides a wide observation window for the application in optical limiter. The low fluorescent quantum yields and detectable room temperature phosphorescence indicate that the system-cross quantum yields of the title complexes containing Pt(II) is effective because of the spin-orbit coupling between the d orbitals of the Pt(II) and the large π-conjugated system. The first-order polarizabilities |βxxx| was determined by the solvatochromic method between 1.02 × 10−29 to 3.46 × 10−28 (cm5/esu).

Polymorph, assembly, luminescence and semiconductor properties of a quinacridone derivative with extended π-conjugated framework

The structures and properties of an indole-ring-fused quinacridone derivative 5,8,15,18-tetraoctyl-5,8,15,18-tetrahydroindolo[3,2-a]indole[3′,2′ : 5,6]quinacridone (IDQA), which was synthesized by an improved procedure, have been carefully investigated and compared with its parent compound N,N′-di(n-octyl)quinacridone (C8-QA). Concentration-dependent 1H NMR spectra revealed that the strong aggregations of IDQA existed in solution because of the flat and extended π-conjugation. Two polymorphs of IDQA with and without π⋯π interactions exhibited red and non emissions, respectively. One-dimensional micromaterials with different morphologies constructed by IDQA molecules were fabricated by a reprecipitation approach and they displayed different emission properties due to the different molecular packing. The nine-ring fused flat skeleton endowed this material with several elegant properties, including a high photoluminescent quantum yield in solution, and a high thermal and electrochemical stability. Therefore, the efficient doped organic light emitting device (OLED) with IDQA as the emitter was fabricated. Moreover, the large π-conjugation system endowed the IDQA thin film with ordered molecular packing and good hole transport properties (hole mobility μh = 0.047 cm2 V−1 s−1).

Deposition of π-Conjugated Polycyanate Ester Thin Films and Their Dielectric Properties

Two kinds of novel π-conjugated polycyanate esters, namely the plasma-polymerized 4-methoxyphenol cyanate ester (PPMPCE) and the plasma-polymerized 4-phenylphenol cyanate ester (PPPPCE), were successfully prepared by plasma polymerization for the first time. The structure and compositions of both plasma polycyanate esters were investigated by Fourier Transform Infrared (FT-IR), X-ray Photoelectron Spectroscopy (XPS) and UV–Visible Absorption Spectra (UV–Vis). The results show that extensively conjugated C=N double bonds were formed in the plasma-deposited cyanate ester thin films, the plasma polymerization of both monomers proceeded mainly via the opening of π-bonds of the O–C≡N functional groups which are further on being formed into a large π-conjugated system, this unique process is noticeably different from the conventional thermal polymerization reaction of cyanate ester monomers. Further dielectric measurement shows that PPPPCE thin film gives a lower dielectric constant comparing to that of the PPMPCE film, and the dielectric constant of both plasma deposited thin films decreased with an increase in measurement frequency.

Deposition and Characterization of a Low-ε r Thin Film Based on Plasma-Polymerized 4-Cumylphenol Cyanate Ester

A novel low-εr polycyanurate film, plasma-polymerized 4-cumylphenol cyanate ester (PPCPCE) film is prepared by plasma deposition of 4-cumylphenol cyanate ester (CPCE). Different from the conventional thermal polymerization of cyanate ester monomers, the plasma polymerization of CPCE proceeds mainly via the opening of π-bonds of the O–CN cyanate ester functional groups which are further formed into a large π-conjugated system[0]. Structural and morphology characterizations show that a smooth and homogenous PPCPCE film with a large π-conjugated system and a high retention of the aromatic ring structure can be obtained at a lower discharge power of 5 W, which gives a low-εr of 2.51. A higher discharge power brings about more severe molecular fragmentation and a significantly rougher film surface.

Synthesis and Dielectric Property of Novel Conjugated Polynitriles From Cyanate Ester

A novel conjugated polynitrile based on cyanate ester, plasma-polymerized 4-cumylphenol cyanate ester (PPCPCE) is synthesized by plasma polymerization of 4-cumylphenol cyanate ester (CPCE) for the first time. The structural characterizations show that the plasma polymerization of CPCE proceeded mainly via the opening of π-bonds of the OCN cyanate ester functional groups which are further on being formed into a large π-conjugated system[0], which is quite different from the conventional thermal polymerization reaction of cyanate ester monomers, in which the cyanate ester monomer undergoes thermal polycyclotrimerization to form polycyanurate containing triazine ring structure. Moreover, the obtained PPCPCE thin film exhibits a low dielectric constant (εr), which might be a potential new candidate to be used as intermetallic dielectrics in microelectronics.

New Progress of Researches in Fluorene Compounds

Fluorene and its derivatives are important compounds, which have biphenyl structure with rigid plane, as well as large π-conjugated system. These special structures of fluorene compounds endow their distinct various functions, properties and biological activities, as well as wide potential application in photoelectrical materials, medicinal agents and so on. More importantly, the fluorene compounds are easily modified and various functional groups could be conveniently introduced into the fluorene ring. The syntheses of fluorene derivatives and their potential applications were extensively investigated and have been become highly active highlight in recent years, and the progress is quite rapid. Combining with our researches and refer- ring other works from literatures, this paper systematically reviews the recent advance in the research and development of fluorene in organic electro-luminescence materials, two-photon absorbing materials, photochromic materials, solar cells, me- dicinal chemistry and so on. The perspectives of the foreseeable future are also presented. Keywords fluorene; organic light emitting materials; solar cell; two-photon absorption; photochromic; biosensor

π−π Interactions and Solid State Packing Trends of Polycyclic Aromatic Bowls in the Indenocorannulene Family: Predicting Potentially Useful Bulk Properties

Solid state crystal structures are discussed and compared for all seven members of the indenocorannulene family that have been recently synthesized by iterative microwave-assisted intramolecular arylations and characterized by single crystal X-ray diffraction. These bowl-shaped polyaromatic hydrocarbons include monoindenocorannulene (C26H12), two isomers each of diindenocorannulene (C32H14) and triindenocorannulene (C38H16), tetraindenocorannulene (C44H18), and pentaindenocorannulene (C50H20), with all molecules mapping onto the geodesic framework of the C60-fullerene. This extended family of π-bowls represents a unique case of a stepwise build-up of size, curvature, and strain at the corannulene core. It allows the first evaluation of the effects of controlled extension of nonplanar π-aromatic surfaces on the solid state structures of the resulting crystalline solids. First, a face-to-face π−π alignment of individual bowls to form 1D stacks is considered and compared for all the above indenocorannulenes having different numbers and different positioning of indeno-groups fused to the corannulene core. Second, the orientations of these 1D columns with respect to each other and their secondary interactions are analyzed. Interesting packing trends and crystal structure variations are found as the size and the curvature of the π-bowls increase. These large π-conjugated carbon-rich systems constitute promising new materials for applications in molecular electronics, with the key to unlocking their specific and unique properties lying in the solid state packing and intermolecular interactions of the individual π-bowls. A thorough analysis of the crystalline structures of the indenocorannulene family, augmented by DFT calculations, has allowed the first predictions of their bulk materials properties.

A Nanoscale Jigsaw‐Puzzle Approach to Large π‐Conjugated Systems

Ein Puzzlespiel: Ein einfaches Modell für die Stabilität konjugierter Kohlenstoff-Hybridmaterialien wird vorgestellt und rechnerisch verifiziert. Auf dieser Grundlage wird eine einfache „Puzzle“-Strategie für das Design solcher Hybridmaterialien vorgeschlagen (siehe Bild; C grün, N blau, H weiß). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Counterion-Dependent Valence Tautomerization of Ferrocenyl-Conjugated Pyrylium Salts

1-Ferrocenylethynylanthraquinone (1-FcAq), which is a donor (D)-acceptor (A) conjugated compound consisting of a ferrocene (Fc) acting as a donor, an anthraquinone (Aq) acting as an acceptor, and an ethynyl linker, undergoes a cyclocondensation reaction with strong organic acid, and forms 2-ferrocenyloxodihydrodibenzochromenylium salts ([1-FcPyl](+)X(-) where X = TFSI, TfO, PF(6), and BF(4)). [1-FcPyl](+) were also characterized as conjugated donor-acceptor compounds, and electrochemical properties, UV-vis absorption spectra, single-crystal X-ray analysis, and TD-DFT calculations have indicated that the LUMO level of [1-FcPyl](+) is lower than that of 1-FcAq because of the much larger pi-conjugated system in [1-FcPyl](+). Variable-temperature Mossbauer spectroscopy (12-300 K) showed that Fe(II) was dominant for the TFSI(-), PF(6)(-), and BF(4)(-) salts of [1-FcPyl](+); although the Fe(III) species was also observed at all temperature ranges, the molar ratio of Fe(III) species increased at higher temperatures in the TFSI(-) and PF(6)(-) salts. This finding indicates that valence tautomerization (VT) between 1-FcPyl(+) and 1-Fc(+)Pyl occurs in the solid state of the TFSI(-) and the PF(6)(-) salts, but not in the BF(4)(-) salt. Variable-temperature (3.5-310 K) IR spectroscopy showed that the frequencies of the skeletal vibration of the ferrocene moiety decreased with increasing temperature in the TFSI(-) and PF(6)(-) salts, indicating the development of a ferrocenium-like character. The precision of the bond lengths of the [1-FcPyl](+) moiety (0.003-0.004 A) determined by single-crystal X-ray analysis (113 and 273 K) is not sufficient to demonstrate the effect of the counterion on VT. The dihedral angle between the ferrocene and the pyrylium moieties in the BF(4)(-) salt (11.25(15) degrees) is larger than that in the TFSI(-) (6.63(12) degrees) and PF(6)(-) (9.55(15) degrees) salts. Furthermore, the planarity of the acceptor moiety (estimated from the dihedral angle between Ph1 and Ph2) is lower in the BF(4)(-) salt compared with that of other salts. These increased dihedral angles might cause a weaker D-A interaction and a destabilization of the acceptor moiety (i.e., raising a LUMO level), leading to lower stability of the Fe(III) (1-Fc(+)Pyl) species. Variable-temperature X-ray powder diffraction (VT XRPD, 100-300 K) revealed that the temperature dependence of the Fe-P distance in the PF(6)(-) salt was smaller than that of the Fe-B distance in the BF(4)(-) salt. Our interpretation of this phenomenon is that the molar ratio of the Fe(III) species is increased in the PF(6)(-) salt, and that the Coulombic force between the ferrocene moiety and PF(6)(-) anion increases, preventing an increase in the Fe-P distance. This indicates that the electrostatic interaction between the [1-FcPyl](+) moiety and the counteranion may affect the occurrence of VT.

A photoluminescent 3D silver(I) coordination polymer with mixed ligands anthracene-9,10-dicarboxylate and hexamethylenetetramine, showing binodal 4-connected (4 3·6 3) 2(4 2·6 2·8 2) 3 topology

The reaction of AgClO 4 with anthracene-9,10-dicarboxylic acid (H 2 L) and hexamethylenetetramine ( hmt) in the presence of 2,6-dimethylpyridine afforded a photoluminescent three-dimensional (3D) Ag I coordination polymer {[Ag 8( L) 3(μ 4- hmt) 2(H 2O) 6](ClO 4) 2} ∞ ( L = anthracene-9,10-dicarboxylate) exhibiting binodal 4-connected (4 3·6 3) 2(4 2·6 2·8 2) 3 topological network. The relevant result reveals that the anthracene skeleton of L ligand bearing a large π-conjugated ring system plays an important role in the formation of the final structure.

P-Quinquephenyl diamine, C 6H 5– p-C 6H 4– p-C 6H 2(2,3-NH 2)– p-C 6H 4–C 6H 5, and its corresponding diimine–Ru(II) complex: Crystal structure and electrochemical and optical properties

The molecular structure of an o-phenylenediamine unit-containing oligophenylene ( 1), Ph–Ph′–Ph′(2,3-NH 2)–Ph′–Ph (Ph = phenyl; Ph′ = p-phenylene; Ph′(2,3-NH 2) = 2,3-diamino- p-phenylene), was determined by X-ray crystallography. 1 has a twisted structure, and forms an intermolecular C–H⋯π interaction network. The –NH 2 group of 1 was air-oxidized to an imine, NH, group in the presence of [RuCl 2(bpy) 2] (bpy = 2,2′-bipyridyl) and gave a ruthenium(II)–benzoquinone diimine complex [Ru( 2)(bpy) 2](PF 6) 2 ( 2: Ph–Ph′–Ph′(2,3-imine)–Ph′–Ph). The molecular structure of [Ru( 2)(bpy) 2](PF 6) 2 was confirmed by X-ray crystallography. [Ru( 2)(bpy) 2](PF 6) 2 underwent two-step electrochemical reduction with E 1/2 = −0.889 V and −1.531 V versus Fc +/Fc. The E 1/2’s were located at higher potentials by 91 mV and 117 mV, respectively, than those of reported [Ru(bqdi)(bpy) 2](PF 6) 2 (bqdi = benzoquinone diimine). Electrochemical oxidation of [Ru( 2)(bpy) 2](PF 6) 2 occurred at a lower potential by 180 mV than that of [Ru(bqdi)(bpy) 2](PF 6) 2. Occurrence of the easier reduction and oxidation of [Ru( 2)(bpy) 2](PF 6) 2 than those of [Ru(bqdi)(bpy) 2](PF 6) 2 is ascribed to the presence of a large π-conjugation system in 2.

Deposition of plasma conjugated polynitrile thin films and their optical properties

The plasma polymerization of 4-phenylbenzonitrile was carried out with the objective of synthesizing a novel conjugated polynitrile thin film with a better optical property. The structure, compositions and morphology of the plasma-polymerized 4-phenylbenzonitrile (PPBPCN) thin films were investigated by Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). A fine, homogenous PPBPCN film with a large π-conjugated system and a high retention of the aromatic ring structure of the starting monomer in the deposited plasma films is obtained when a low discharge power of 30 W was used during film formation. For the first time, a blue emission with relatively high photoluminescence intensity for PPBPCN thin films was observed.

Preparation of poly(3,3′-dialkynyl-2,2′-bithiophene-5,5′-diyl) with high coplanarity and effective π-conjugation system

New head-to-head type polythiophenes with acetylenic –C CR side groups, HH-P3(C CR)Th (R= n-C 10H 21, n-C 6H 13, n-C 4H 9), were prepared by palladium-catalyzed polycondensation of the corresponding dibromo-monomers by using Me 3SnSnMe 3 as the polycondensing agent. The single crystal structure of the monomer revealed high coplanarity of the bithiophene unit, and the derived polymer showed a UV–vis absorption peak at approximately 520 nm. The λ max position was red-shifted from those of regioregular poly(3-alkylthiophene)s (385 and 430 nm for HH- and HT-type polymers, respectively). These data indicate that the newly synthesized polythiophene with the –C CR group has a highly coplanar structure with a large effective π-conjugation system.

Synthesis, Characterization, and Optical Properties of New Two-Photon-Absorbing Fluorene Derivatives

The synthesis of a series of four new compounds containing fluorenyl chromophores is presented, along with the results of spectroscopic and photochemical studies aimed at understanding the two-photon absorption properties and energetics of their electronically excited states. The molecular structures of the compounds were systematically varied to allow comparison of molecules possessing high and low molecular symmetry, short and long alkyl chains, and a fluorenyl conjugated π-system. Solvent-dependent absorption and emission were investigated along with π-conjugation length. Preliminary measurements of two-photon absorption (2PA) using a two-photon fluorescence method indicate that these chromophores exhibit high two-photon absorptivity. A symmetrical molecule (3), possessing a relatively large π-conjugated system, flanked on either side by electron-withdrawing groups (benzothiazole), exhibited a peak 2PA cross section (δ) of 6000 × 10-50 cm4 s photon-1 molecule-1 at 600 nm. Excitation anisotropy studies revealed the position of the S0 → S1 and S0 → S2 electronic transitions. Consistent with quantum mechanical selection rules, the two-photon allowed transition (S0 → S2) was dominant.

Large and ultrafast third-order optical nonlinearity of heteroleptic triple-decker (phthalocyaninato)(porphyrinato)Sm(III) complexes

The third-order optical nonlinearity of two triple-decker mixed phthalocyaninato and porphyrinato Sm complexes, Sm 2(Pc) 2(TPP) and Sm 2(Pc)(TPP) 2 (Pc=phthalocyanine; TPP=5,10,15,20-tetraphenylporphyrinate), is investigated using the femtosecond time-resolved optical Kerr gate method at 830 nm wavelength. Their second-order hyperpolarizabilities are estimated to be 2.6 × 10 −30 and 2.2 × 10 −30 esu, respectively. Introducing of Lanthanide Sm to the large π-conjugated system, intermacrocycle interaction and two-photon resonance are considered responsible for the large optical nonlinearity.

Compression of the dye monolayer at the air/water interface studied by second harmonic generation

The second harmonic (SH) generation efficiency upon compression of insoluble rhodamine C18 and fluorescein O322 monolayers at the air/water interface has been measured. The SH intensity dependence on area per molecule clearly varied for four main regions: expanded monolayer, expanded–condensed transition region, condensed monolayer and collapse point. This SH intensity dependence was similar with the π–A isotherm for both molecules. The SH intensity change would be explained with a model of interactions of dye chromophores based on the dipole–dipole correlation, CH-π interaction, aggregates of electronic transition moments and formation of large order π-conjugated system.

New soluble poly(fluoro-diacetylene)s with a large π-conjugation system

New soluble poly(fluoro-diacetylene)s with fluoro-aromatic rings directly bound to an extended π-conjugated backbone have been generated via solid-state polymerization induced by thermal annealing. The large π-conjugated backbones of these soluble poly(fluoro-diacetylene)s have been established by means of UV-vis spectra.