Layer-block dendrimers with alternating thienylenevinylene and phenylenevinylene units

A series of new hybrid, layer-block π-conjugated dendrons and dendrimers with alternating thienylenevinylene and phenylenevinylene units has been prepared by means of an orthogonal and convergent-growth methodology that made use of the Horner-Wadsworth-Emmons (HWE) reaction. The placement of the thiophene and benzene rings can be accurately controlled to afford a large variety of dendritic structures, although access to compounds of high generation proved difficult. The optical properties of the synthesized dendrimers were determined by UV/vis and fluorescence spectroscopy, and the influence of the generation and nature of the core on the behavior of these materials was evaluated.     

M···π-conjugated complexes: simple materials with dramatic NLO features (M = Li,Na, K,and π = butadiene,cyclobutadiene, hexatriene,benzene)

Theoretical investigation of linear and nonlinear optical (NLO) properties in simple complexes consist of alkali metals and π-conjugated systems have been studied at MP2/6-311++G(2d,2p) computational level. Lithium, sodium, and potassium as alkali metals were chosen for interaction with some non-aromatic, aromatic and anti-aromatic systems. For better comparison of results, the π-systems were chosen with the same carbon number: butadiene as a non-aromatic in comparison with cyclobutadiene as an anti-aromatic and hexatriene as a non-aromatic in comparison with benzene as an aromatic system. Results revealed that gap energy of studied π-systems was decreased under the interacting with alkali metals. Furthermore all designed complexes were shown very good results in average polarizability (α) and first hyperpolarizability (β ₀) parameters. So these very simple dimer complexes could be introduced as promising innovative nonlinear optical materials.     

Effect of acceptor heteroatoms on π-hydrogen bonding interactions: A study of indole⋅⋅⋅thiophene heterodimer in a supersonic jet

Resonant two photon ionization (R2PI), IR-UV, and UV-UV double resonance spectroscopic techniques combined with quantum chemistry calculations have been used to determine the structure of indole???thiophene dimer observed in a supersonic jet. With the help of combined experimental and theoretical IR spectra it has been found that the observed dimer has a N-H???π hydrogen bonded slanted T-shaped structure. The present study demonstrates the effect of heteroatoms present in the acceptors on the strength of the π-hydrogen bonding interactions. It was concluded by Sherrill and co-workers from their theoretical study of benzene???pyridine dimer that aromatic rings containing heteroatoms are poorest π-hydrogen bond acceptors [E. G. Hohenstein and C. D. Sherrill, J. Phys. Chem. A 113, 878 (2009)]. But the current spectroscopic investigation exhibits that five membered aromatic heterocycles are favorable π-hydrogen bond acceptors. In this study, it has also been shown that thiophene is a better π-hydrogen bond acceptor than furan. The present work has immense biological significance as indole is the chromophore of tryptophan residue in the proteins and thiophene derivatives have potential therapeutic applications. Thus, understanding the binding motif between indole and thiophene in the heterodimer studied in this work may help in designing efficient drugs.     

Heterocyclic Chromophore Amphiphiles and their Supramolecular Polymerization

Supramolecular polymerization of π-conjugated amphiphiles in water is an attractive approach to create functional nanostructures. Here, we report on the synthesis, optoelectronic and electrochemical properties, aqueous supramolecular polymerization, and conductivity of polycyclic aromatic dicarboximide amphiphiles. The chemical structure of the model perylene monoimide amphiphile was modified with heterocycles, essentially substituting one fused benzene ring with thiophene, pyridine or pyrrole rings. All the heterocycle-containing monomers investigated underwent supramolecular polymerization in water. Large changes to the monomeric molecular dipole moments led to nanostructures with low electrical conductivity due to diminished interactions. Although the substitution of benzene with thiophene did not notably change the monomer dipole moment, it led to crystalline nanoribbons with 20-fold higher electrical conductivity, due to enhanced dispersion interactions as a result of the presence of sulfur atoms.     

Nonlinear optical properties of alkalides Li+(calix[4]pyrrole)M- (M = Li, Na, and K): alkali anion atomic number dependence

A new type of alkalide compound, Li+(calix[4]pyrrole)M- (M = Li, Na, and K), is presented in theory, which may be stable at room temperature. It has been shown by our calculations that the first hyperpolarizability (beta) is considerably large by means of the density functional theory method. The beta values are determined at the B3LYP/6-311++G level (for the alkali atoms the 6-311++G(3df) basis set is employed) as 8.9 x 103, 1.0 x 104, and 2.4 x 104 au for M = Li, Na, and K, respectively. These beta values are much larger than that of electride Li+(calix[4]pyrrole)e- (beta = 7.3 x 103 au) by a factor of 1.2 to 3.4. Comparing to the cryptand calix[4]pyrrole, the beta values of Li+(calix[4]pyrrole)M- are enhanced by 20-60 times. It is revealed, for the first time, that the beta value of alkalide compounds depends on the atomic number of the alkali anion, and it can be enhanced by choosing the akali anions with larger atomic numbers. The alkali anion in the alkalide compound decreases the transition energy and also increases the oscillator strength of the main transition, consequently the beta value is enhanced. This study proposes such a novel way to synthesize and design new NLO materials by using the alkali atom with a larger atomic number to create an anion in alkalide compounds.     

Commercially available simple ionic liquids-promoted dehydrative carbon–carbon bond-forming reaction of diarylmethanols and triarylmethanols with pyrroles,thiophene, furan and indoles

Two commercially available simple ionic liquids, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 1-ethyl-2,3-dimethylimidazolium trifluoromethansulfonate, effectively promote the solvent-free dehydrative carbon–carbon (C–C) bond-forming reaction of a variety of diarylmethanols and triarylmethanols with π-rich heteroaromatics, such as pyrroles, indole, furan, and thiophene without ring-opening and polymerization to give the corresponding not only 2-substituted pyrroles, furan, and thiophene but also 3-substituted indoles in good to excellent yields with moderate to excellent regioselectivities. These dehydrative C–C bond formation reactions of alcohols offer several advantages, such as the use of stoichiometric amounts of π-rich heteroaromatics and ionic liquids, water is the only by-product, there is no need for either organic solvents or expensive metal or strong Brønsted acid catalysts in the reaction, and the diversity of diarylmethylation and triarylmethylation.     

Photophysics,Electrochemistry and Efficient Electrochemiluminescence of Trigonal Truxene-Core Dyes

We synthesized and characterized a series of dyes built from a spirofluorene or truxene core. The quadrupolar spirofluorene system is the initial building unit for the design and preparation of more complex star-shaped dyes consisting of a truxene core bearing three di- or triphenylamine moieties with or without a thiophene connector. Their photophysical, electrochemical, and electrochemiluminescence (ECL) properties were first investigated in solution. Structure/activity relationships were derived and rationalized by comparing the quadrupolar system and trigonal truxene-core derivatives using computational studies. The photophysical and redox characteristics are drastically tuned by the introduction of a thiophene bridge and electron-donor substituents at their terminal branches. These comparative studies show the essential role of the stability of both radical cations and anions to obtain efficient ECL dyes. The stabilization of the radicals is directly related to the charge delocalization due to the π-conjugation by the thiophene bridge. The brightest ECL is achieved by annihilation and coreactant (benzoyl peroxide) pathways with the blue-emitting truxene dye, which is 2- and 4.5-times greater than that of the quadrupolar compound and reference [Ru(bpy)₃]²⁺ emitter, respectively. Such an extensive study on these extended π-conjugated molecules presenting different core structures may guide the design and synthesis of new ECL dyes with a strong efficiency.     

Group 15 pnictenium cations supported by a conjugated bithiophene backbone

Thiophene based polymers and oligomers have attracted considerable attention because they can be functionalized to alter the gap between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), which enables the design of tunable light emitting materials. One area, which has been less explored, is the incorporation of low coordinate, low oxidation state main group elements into these systems. We have currently developed a novel π-conjugated ligand containing two contiguous thiophene rings in which we have demonstrated its ability to support both pnictogen cations and their metal complexes.     

Theoretical studies on structures and nonlinear optical properties of alkali doped electrides B12N12–M (M = Li,Na, K)

The structures and nonlinear optical properties of a novel class of alkali metals doped electrides B₁₂N₁₂–M (M = Li, Na, K) were investigated by ab initio quantum chemistry method. The doping of alkali atoms was found to narrow the energy gap values of B₁₂N₁₂ in the range 3.96–6.70 eV. Furthermore, these alkali metals doped compounds with diffuse excess electron exhibited significantly large first hyperpolarizabilities (β₀) as follows: 5571–9157 au for B₁₂N₁₂–Li, 1537–18,889 au for B₁₂N₁₂–Na, and 2803–11,396 au for B₁₂N₁₂–K. Clearly, doping of the alkali atoms could dramatically increase the β₀ value of B₁₂N₁₂ (β₀ = 0). Furthermore, their transition energies (ΔE) were also calculated. The results showed that these compounds had low ΔE values in the range 1.407–2.363 eV, which was attributed to large β₀ values of alkali metals doped B₁₂N₁₂ nanocage. © 2016 Wiley Periodicals, Inc.     

Quadratic hyperpolarizabilities of nitro-substituted pseudo-linear dye molecules with ethylenic and azo bridges

Second-order hyperpolarizabilities (β) and gas-phase transition energies (E) of the para-disubstituted benzene, stilbene and azobenzene derivatives are calculated by the semi-empirical self-consistent-field molecular orbit (SCF MO) method in the Pariser-Parr-Pople (PPP) approximation using a sum-over-state's procedure with singly excited states. The calculated zero-frequency β (β⁰_VEC) values for all the derivatives are directly proportional to their 1/E² values. The usefulness of mixing ethylenic and azo bridges in long π-conjugated molecules is proposed in order to obtain large β values, by taking the difference between the electronic natures of these bridges into account. © 1996 John Wiley & Sons, Inc.     

Cu(I), Ag(I)/分子筛化学吸附脱硫的π-络合机理

应用DFT 研究了一系列含硫的杂环化合物(噻吩、苯并噻吩、二苯并噻吩和4, 6-二甲基二苯并噻吩)以及苯分子在Cu(I)-Y、Ag(I)-Y 分子筛上的化学吸附. 计算采用16T 分子筛簇模型(H22Si15AlO22), 对过渡金属采用了赝势基组, 在BLYP/DNP水平上完成. 相互作用能的结果表明, 阳离子交换的分子筛对含硫杂环芳香族化合物吸附能力的顺序为Cu(I)-Y >Ag(I)-Y. 两种吸附剂对噻吩类分子的吸附能力大于苯分子. 噻吩衍生物的吸附能顺序依次为, 4, 6-二甲基二苯并噻吩<二苯并噻吩约噻吩<苯并噻吩, 与实验结果相近. 通过自然键轨道计算,研究了分子筛上担载的Cu(I)、Ag(I)金属离子与噻吩和苯分子之间的π-络合作用, 分析比较了自然键电子给体-受体之间的二阶微扰稳定化能, 并探索其络合机理.     

聚（3，4-二氯）噻吩的制备及表征

以四氯噻吩为原料,采用化学合成法制备了聚（3,4-二氯）噻吩．对影响合成材料结构规整度的溶剂极性进行了初步探讨,并采用元素分析、红外光谱、^13C NMR核磁谱等对目标产物进行了表征．结果表明,当采用极性较低的乙二醇二甲醚作溶剂时,可得到规整度较高的目标产物．     

Synthesis of a new diarylethene diradical which has extended π-conjugated chains from the 2,5-position of one thiophene ring

A diarylethene diradical having a new switching unit for intramolecular magnetic interaction was synthesized. The photoswitching unit has an extended π-conjugated chain in one aryl unit, and two nitronyl nitroxide radical are placed at both ends of the π-conjugated chain. The diarylethene moiety is located in the middle of the chain. This diarylethene is designed to change the hybrid orbital from sp² to sp³ at the 2-position of the thiophene ring when this diarylethene undergoes a photochromic reaction. But the new diradical compound did not undergo photocyclic reaction upon irradiation with UV light. The photochemical behavior is perturbed by a resonant quinoid structure which stabilizes the open-ring isomer.     

Highly Efficient Luminescent Solar Concentrators Based on Benzoheterodiazole Dyes with Large Stokes Shifts

Five extended π-conjugated systems with electron donor (D) and acceptor (A) moieties have been synthesized. Their basic D-A-D structural motif is a benzothiadiazole unit symmetrically equipped with two thiophene rings ( S2T ). Its variants include 1) the same molecular framework in which sulfur is replaced by selenium ( Se2T ), also with four thiophene units ( Se4T ) and 2) a D’-D-A-D system having a N-carbazole donor moiety at one end ( CS2T ) and a D’-D-A-D-A’ array with a further acceptor carbonyl unit at the other extremity ( CS2TCHO ). The goal is taking advantage of the intense luminescence and large Stokes shifts of the five molecules for use in luminescent solar concentrators (LSCs). All of them exhibit intense absorption spectra in the UV/Vis region down to 630 nm, which are fully rationalized by DFT. Emission properties have been studied in CH₂Cl₂ (298 and 77 K) as well as in PMMA and PDMS matrices, measuring photoluminescence quantum yields (up to 98 %) and other key optical parameters. The dye–PMMA systems show performances comparable to the present state-of-the-art, in terms of optical and external quantum efficiencies (OQE=47.6 % and EQE=31.3 %, respectively) and flux gain (F=10.3), with geometric gain close to 90. LSC devices have been fabricated and tested in which the five emitters are embedded in PDMS and their wave-guided VIS luminescence feeds crystalline silicon solar cells.     

Cation-pi interactions with a model for the side chain of tryptophan: structures and absolute binding energies of alkali metal cation-indole complexes

Threshold collision-induced dissociation techniques are employed to determine bond dissociation energies (BDEs) of mono- and bis-complexes of alkali metal cations, Li+, Na+, K+, Rb+, and Cs+, with indole, C8H7N. The primary and lowest energy dissociation pathway in all cases is endothermic loss of an intact indole ligand. Sequential loss of a second indole ligand is observed at elevated energies for the bis-complexes. Density functional theory calculations at the B3LYP/6-31G level of theory are used to determine the structures, vibrational frequencies, and rotational constants of these complexes. Theoretical BDEs are determined from single point energy calculations at the MP2(full)/6-311+G(2d,2p) level using the B3LYP/6-31G* geometries. The agreement between theory and experiment is very good for all complexes except Li+ (C8H7N), where theory underestimates the strength of the binding. The trends in the BDEs of these alkali metal cation-indole complexes are compared with the analogous benzene and naphthalene complexes to examine the influence of the extended pi network and heteroatom on the strength of the cation-pi interaction. The Na+ and K+ binding affinities of benzene, phenol, and indole are also compared to those of the aromatic amino acids, phenylalanine, tyrosine, and tryptophan to elucidate the factors that contribute to the binding in complexes to the aromatic amino acids. The nature of the binding and trends in the BDEs of cation-pi complexes between alkali metal cations and benzene, phenol, and indole are examined to help understand nature's preference for engaging tryptophan over phenylalanine and tyrosine in cation-pi interactions in biological systems.     

Structures and considerable static first hyperpolarizabilities: new organic alkalides (M+@n6adz)M'- (M, M'=Li, Na, K; n=2, 3) with cation inside and anion outside of the cage complexants

Eighteen structures of new organic alkalides (M+@n6adz)M'- (M, M'=Li, Na, K; n=2, 3) with the alkali-metal cation M+ lying near the center of the adz cage and the alkali-metal anion M'- located outside are obtained with all real frequencies. They exhibit very large static first hyperpolarizabilities (beta0) up to 3.2x10(5) au, which exceeds the record value of beta0=1.7x10(5) au for nonlinear optical compounds [Chem.-Eur. J. 1997, 3, 1091]. All potassides (M+@n6adz)K- (M=Li, Na, K; n=2, 3) have considerably large beta0 values (1.6x10(5)-3.2x10(5) au) much larger than the beta0 value (3.6x10(4) au) of the previously designed cuplike alkalide Li+(calix[4]pyrrole)K- [J. Am. Chem. Soc. 2006, 128, 1072]. This shows that the 26adz and 36adz cage complexants are preferable to cuplike calix[4]pyrrole complexant in enhancing the first hyperpolarizability. The effect of cage size of the complexant on the first hyperpolarizability is also presented here: in most cases, the smaller cage complexant corresponds to the larger beta0 value. Moreover, the crucial role by the alkali-metal anion in the large first hyperpolarizability of these alkalides is revealed. These results may provide new means for designing high-performance nonlinear optical materials.     

Non-classical heteroacenes: synthesis and properties of anthra[2,3-c:6,7-c']dithiophene derivatives

A new class of linear heteroacenes, anthra[2,3-c:6,7-c']dithiophenes, containing non-classical (non-Kekulé) thiophene in a 22-electron π-conjugated system have been prepared by electrochemical reduction. The electronic properties have been studied by DFT calculations and spectroelectrochemistry, supporting the formation of a triplet electronic structure.     

改性Ｙ型分子筛的吸附脱硫性能以及苯，萘对吸附的影响

采用离子交换法制备了经金属离子改性的Y型分子筛吸附剂, 并用XRF, XRD, XPS对吸附剂的化学组成, 晶相结构等进行了表征. 以含噻吩, 苯并噻吩的辛烷溶液为模型燃料考察了吸附剂的吸附脱硫性能以及苯, 萘对脱硫的影响. 结果表明, Cu(Ⅰ)Y, CuZnY具有较大的吸附容量, 而苯对苯并噻吩吸附脱除性能几乎没有影响, 但对噻吩的吸附性能影响较大, 萘对苯并噻吩和噻吩的脱除都有较大的抑制作用. 并由此推测, 吸附剂与苯并噻吩或萘的结合比噻吩或苯更紧密, 吸附的机理是π络合.     

Synthesis and properties of novel C3-symmetric coplanar chromophores

New synthetic pathways for novel C(3)-symmetric molecules featured with a thiophene-fused six-five-five carbon-bridged coplanar core structure have been established. The incorporation of thiophene as the constituent of a C(3)-symmetric core provides effective modulation of the physical properties and imparts extra flexibility for π-conjugated functionalization stemming from either the embedded thiophene or pendant aryl substitutions.     

Molecular electrostatic potential for exploring π-conjugation: a density-functional investigation

Molecular electrostatic potentials (MESP) of the most common building blocks of organic π-conjugated systems, viz. ethylene, acetylene, benzene, furan, pyrrole, thiophene and phenylvinylene, are examined at the B3LYP/6-311++G(2d,2p) level. The topography of MESP is employed for mapping the strength of electronic conjugation between these building blocks. When electron-rich molecular regions are connected to each other, the MESP value of the corresponding conjugation critical point (CCP) is able to provide a quantitative measure of the strength of the conjugation. The systems with stronger conjugation are generally seen to possess a larger negative value of CCP and a smaller difference (ΔV(CM-CCP)) between the MESP values of respective conjugated minimum (CM) and the CCP, in agreement with the experimental as well as other theoretical results. The present MESP topography-based approach thus offers a measure of the quantitative strength of π-conjugation in molecules.