Binaphthalene molecules with tetrathiafulvalene units: CD spectrum modulation and new chiral molecular switches by reversible oxidation and reduction of tetrathiafulvalene units

By combining the features of binaphthalene and tetrathiafulvalene (TTF), compounds 1-4 were designed for studies of chiral molecular switches. Absorption and CD spectral studies clearly indicate that the CD spectra resulting from axial chiral binaphthalene units can be modulated through the redox reactions of TTF units, which means new chiral molecular switches can be established on the basis of binaphthalene molecules with TTF units. The reference compound 5, which has one TTF unit rather than two as in the case of compounds 1, 3, and 4, failed to show such property, hinting that the presence of two or more TTF units is required for the realization of CD spectrum modulation. In addition, the manner of the CD spectrum modulation has been found to be dependent on the way TTF units are linked to the binaphthalene skeleton, in terms of the linker length, the positions for substitution, and the number of TTF units.     

An Hg2+-gated chiral molecular switch created by using binaphthalene molecules with two anthracene units and two 1,3-dithiole-2-thione (1,3-dithiole-2-one) units

By integrating the features of anthracene, 1,3-dithiole-2-thione, and binaphthalene units, (S)-1 and its analogue (S)-2, which contains two 1,3-dithiole-2-one units instead of 1,3-dithiole-2-thione, were studied for creating a new molecular regulation system and building a gated chiral molecular switch. The results show that the photodimerization is controlled by the remote functional-group transformation of C=S into C=O, thus providing an elegant example of molecular regulation. The photodimerization of two anthracene units induces circular dichroism (CD) spectral variation. Overall, the CD spectrum can be remotely modulated by Hg2+ in (S)-1, which leads to an Hg2+-gated chiral molecular switch.     

Tuning the CD spectrum and optical rotation value of a new binaphthalene molecule with two spiropyran units: mimicking the function of a molecular "AND" logic gate and a new chiral molecular switch

With the view to developing new chiral molecular switches and logic gates, a new binaphthalene molecule with two spiropyran units (1) was synthesized and characterized. Absorption and 1H NMR spectral studies of 1 after reaction with acid/base indicate acidichromism can occur to compound 1. The synergistic actions of acid and UV light irradiation result in a remarkable change for the CD spectrum of the relatively dilute solution of 1, mimicking the behavior of a chiral "AND" gate, since the "ouput" is the CD signal. Furthermore, the optical rotation value of the relatively concentrated solution of 1 can be reversibly tuned after sequential reactions with acid and base, and thus a chiral molecular switch with nondestructive "output" signal is realized. The present results not only add a new example of chiral molecular switch with nondestructive readout but also provide a chiral "AND" gate based on the axial chiral binaphthalene to which switchable units are linked.     

A chiral low-molecular-weight gelator based on binaphthalene with two urea moieties: modulation of the CD spectrum after gel formation

The synthesis and characterization of a new chiral LMWG 1 based on the axially chiral binaphthalene with two urea moieties were described. A transparent gel in cyclohexane with LMWG 1 was obtained and characterized by SEM, XRD and CD techniques. The results of 1H NMR measurement indicated that the intermolecular H-bonds and pi-pi interaction may be responsible for the gel formation. It was demonstrated that the gel phase could be destroyed by addition of F- due to the disruption of intermolecular H-bonds. After gel formation, modulation of the CD spectrum of 1 was observed.     

Synthesis, helicity, and chromism of optically active poly(phenylacetylene)s carrying different amino acid moieties and pendant terminal groups

Functional phenylacetylene derivatives containing l-alanine and l-leucine moieties with chiral menthyl and achiral n-octyl terminal groups {HC[triple bond]C-C6H4-p-CONHCH(R)CO2R': R = CH3, R'= (-)-(1R,2S,5R)-menthyl [1(-)]; R = CH2CH(CH2)3, R' = (-)-(1R,2S,5R)-menthyl [2(-)]; R'= CH2CH(CH2)3, R' = (+)-(1S,2R,5S)-menthyl [2(+)]; R'= CH2CH(CH2)3, R' = (CH2)7CH3 (2o)} are synthesized. Polymerizations of the acetylene monomers are effected by organorhodium catalysts, giving corresponding polymers P1(-), P2(-), P2(+), and P2o of high molecular weights (Mw up to 1.2 x 10(6)) in high yields (up to 89%). The polymers are thermally stable (Td >or= 300 degrees C) and soluble in common organic solvents. The polymer structures are characterized by IR, NMR, UV, and CD spectroscopies. Intense CD signals are observed in the visible spectral region, indicating that the polymer chains are taking a helical conformation with an excess of preferred handedness. The backbone conjugation and chain helicity of the polymers can be tuned by changing their molecular structures [(a)chiral pendant groups] and by applying external stimuli (solvent and pH). Addition of trifluoroacetic acid to the polymer solutions decreases their molar ellipticities and enhances their backbone conjugations, inducing a halochromism with a continuous and reversible color change (yellow <==> red).     

Naphthalene- and anthracene-based aromatic foldamers with iminodicarbonyl linkers: their stabilities and application to a chiral photochromic system using retro [4 + 4] cycloaddition

A circular dichroism (CD) spectral study on chiral aromatic chain imides possessing anthracene and naphthalene moieties with bulky N substituents showed that their helical chirality based on folding remained for a reasonably long time without racemization in solution. Racemization due to conformational equilibration occurred very slowly, requiring over 1 week at ambient temperature. Their CD spectra both in solution and in the solid state gave similar CD signals, suggesting retention of helicity observed in the solid state even after dissolving. As an application of this novel chiral folding of aromatic chain imides, a chiral photochromic system was investigated based on the photo [4 + 4] cycloaddition and its thermal cycloreversion of an anthracene-naphthalene system. The foldamer possessing an anthracene moiety in the center connected with two naphthalene moieties below and above it by iminodicarbonyl linkers was prepared for this purpose. Induced CD was observed for the foldamer with (S)-1-(1-naphthyl)ethyl substituents at the imide nitrogen atoms. Chiral photochromic cycles were monitored by CD spectral measurement.     

Chemistry of anthracene-acetylene oligomers: synthesis and enantiomeric resolution of a chiral 1,8-anthrylene-ethynylene cyclic tetramer

To construct a new type of chiral pi-conjugated system, the title anthracene-acetylene oligomer containing two octyl groups at position 10 of 1,2-alternating anthracene groups was synthesized. Each anthracene unit was connected by Sonogashira coupling, and the tetrameric precursor was cyclized by a cross-coupling reaction to form the desired C2-symmetric compound. Its enantiomers were resolved by chiral HPLC with a Chiralcel OD column, and the chiroptical properties were investigated by optical rotation ([alpha]D(23) = -95 and +91) and circular dichroism (CD) measurements. The structural and spectroscopic features of this oligomer were discussed in terms of the molecular symmetry and the dynamic behavior of the macrocyclic framework.     

一种新的具有双螺旋结构特征的光学活性分子方的设计、合成及其光学性质

分别从手性构型高度稳定的(R)和(S)-2,2'-二乙炔基-1,1'-联萘模板出发, 通过保护基的控制导入、偶联反应、保护基脱去以及分子间偶合成环4个步骤成功地合成了一种具有螺旋结构特征的新的光学活性分子方(Molecular square)(R,R,R,R)-1和(S,S,S,S)-1. 用MS, IR, UV-Vis, 1H和13C NMR以及元素分析等方法对目标化合物进行了结构表征. 测定并分析比较了2个目标化合物的比旋光度[α]D和圆二色性(CD)等光学性质. 在CH2Cl2溶液中, 异构体(R,R,R,R)-1和(S,S,S,S)-1的[α]25D值分别为+887.3°和-889.7°, 并且其CD谱表现出对称的镜像特征.     

Synthesis and structural and photoswitchable properties of novel chiral host molecules: axis chiral 2,2'-dihydroxy-1,1'-binaphthyl-appended stiff-stilbene

Novel photoswitchable chiral hosts having an axis chiral 2,2'-dihydroxy-1,1'-binaphthyl (BINOL)-appended stiff-stilbene, trans-(R,R)- and -(S,S)-1, were synthesized by palladium-catalyzed Suzuki-Miyaura coupling and low-valence titanium-catalyzed McMurry coupling as key steps, and they were fully characterized by various NMR spectral techniques. The enantiomers of trans-1 showed almost complete mirror images in the CD spectra, where two split Cotton effects (exciton coupling) were observed in the beta-transitions of the naphthyl chromophore at 222 and 235 nm, but no Cotton effect was observed in the stiff-stilbene chromophore at 365 nm. The structures of (R)-10 and trans-(R,R)-1 were confirmed by X-ray structural analysis. The optimized structure of cis-1 by MO calculations has a wide chiral cavity of 7-8 A in diameter, whereas trans-1 cannot form an intramolecular cavity based on the X-ray data. Irradiation of (R,R)-trans-1 with black light (lambda = 365 nm) in CH3CN or benzene at 23 degrees C led to the conversion to the corresponding cis-isomer, as was monitored by 1H NMR, UV-vis, and CD spectra. At the photostationary state, the cis-1/trans-1 ratio was 86/14 in benzene or 75/25 in CH3CN. On the other hand, irradiation of the cis-1/trans-1 (75/25) mixture in CH3CN with an ultra-high-pressure Hg lamp at 23 degrees C (lambda = 410 nm) led to the photostationary state, where the cis-1/trans-1 ratio was estimated to be 9/91 on the basis of the 1H NMR spectra. The cis-trans and trans-cis interconversions could be repeated 10 times without decomposition of the C=C double bond. Thus, a new type of photoswitchable molecule has been developed, and trans-1 and cis-1 were quite durable under irradiation conditions. The guest binding properties of the BINOL moieties of trans- and cis-(R,R)-1 with F-, Cl-, and H2PO4- were examined by 1H NMR titration in CDCl3. Similar interaction with F- and Cl- was observed in trans-1 (host/guest = 1/1, Kassoc = (1.0 +/- 0.13) x 103 for F- and (4.6 +/- 0.72) x 102 M-1 for Cl-) and cis-1 (host/guest = 1/1, Kassoc = (1.0 +/- 0.13) x 103 for F- and (5.9 +/- 0.69) x 10 M-1 for Cl-), but H2PO4- interacted differently: the cis-isomer formed the 1/1 complex (Kassoc = (9.38 +/- 2.67) x 10 M-1), whereas multistep equilibrium was expected for the trans-isomer.     

CD spectra of polynuclear complexes of diimine ligands: theoretical and experimental evidence for the importance of internuclear exciton coupling

We have recently reported on dinuclear complexes Lambda,Lambda-[Co(2)L(2)Cl(2)]CoCl(4) of two novel chiral ligands (1a and 1b) which contain pyridyl-imine chelate groups (Telfer, S. G.; Sato, T.; Kuroda, R. Chem. Commun. 2003, 1064-1065). The absolute configuration of the cobalt(II) centers was unambiguously assigned by X-ray crystallography. However, the sign of the exciton couplets in their CD spectra was opposite to that expected on the basis of the stereochemistry of the metal centers. We present a rationalization of these anomalous spectra in terms of an "internuclear" exciton coupling model which takes into account the coupling of chromophores located on different metal centers. We have performed a series of semiempirical (ZINDO) calculations which provide quantitative support to this model. These findings show that the absolute configuration of the metal centers in a polynuclear complex may be incorrectly assigned on the basis of CD data if internuclear coupling effects are not taken into consideration. We summarize the CD spectral data of number of other chiral polynuclear complexes from the literature, including dinuclear complexes bridged by the 2,2'-bipyrimidine ligand, complexes of the HAT ligand, and dinuclear triple-stranded helicates. The amplitude of the CD spectra of many of these complexes is not additive with the number of chromophores. These anomalous spectra can be accounted for by taking internuclear coupling effects into consideration.     

Host-enhanced π-π interaction for water-soluble supramolecular polymerization

Host-enhanced π-π interaction based on anthracene derivatives and cucurbit[8]uril can be used as the driving force for constructing water-soluble supramolecular polymers. For this purpose, two anthracene moieties were encapsulated into one cucurbit[8]uril cavity, forming a ternary complex. After encapsulation in the host, the distance between the two anthracene moieties was shortened, and the π-π interaction between them was enhanced significantly. To realize supramolecular polymerization, a bifunctional monomer consisting of two anthracene moieties and a short linker in between was carefully designed. Cyclization was avoided in this way. Thus, host-enhanced π-π interaction can function as a new driving force for supramolecular polymerization.     

含手性亚胺侧基聚苯乙烯衍生物的设计及其在酸碱诱导下的手光响应性质

以N-(2-羟基-1-萘基)亚甲基-(S)-α-苯基乙胺为模型分子,考察了脱质子前后该手性Schiff碱溶液手光性质的变化,利用DFT计算探讨手光信号反转机理.结果表明,手光反转源于分子内氢键的断裂与形成及伴随的C—C单键旋转所引起的构象转变,且前后2种构象处于拟对映关系.这一发现意味着通过单键旋转操控分子构象转变可作为构建手性开关的一种有效途径.在此基础上设计、合成了苯乙烯型手性功能单体(VNP)及相应的光学活性聚合物.由于邻位基团的协同效应,聚合物的手光性质对酸碱刺激表现出比单体更灵敏的响应性和可重复性.当循环加入H+和OH-时,聚合物溶液的CD信号(382 nm处的Cotton效应)以"ON"-"OFF"方式发生可逆转变,以此为输出信号可无损耗重复至少5次,实现了通过酸碱调控的无损输出的新型聚合物基手性开关.此外,基于该手性开关体系构建了典型的"禁阻"(IHIBIT)分子逻辑门.     

Solvent and temperature effects on the chiral aggregation of poly(alkylarylsilane)s bearing remote chiral groups.

Novel switchable chiroptical characteristics of poly(alkylarylsilane) microaggregates, controllable by the choice of good/poor solvent ratio (solvent polarity), solvent addition order, and sample temperature are described. The formation of stable chiral aggregates depends critically on the polysilane structure and stereochemistry. Poly[n-hexyl-(p-(S)-2-methylbutoxyphenyl)silane] (1), optically inactive in molecularly dispersed THF solution due to the existence of dynamically equivalent amounts of right (P)- and left (M)-handed screw sense helical main chain domains, shows a marked bisignate CD signal due to the formation of chiral aggregates in good/poor cosolvent systems. The sign and magnitude of the CD signals are dependent on solvent polarity, solvent addition order, and thermal effects. The less sterically hindered poly[methyl-(p-(S)-2-methylbutoxyphenyl)silane] (2) exhibits a weak, bisignate, nonswitchable CD signal in only the toluene/acetonitrile system, and no CD signals are evident in pure toluene or THF due to masking of the helicity. In contrast, although the even less sterically hindered, less polar poly[methyl-(m-(S)-2-methylbutoxyphenyl)silane] (3) does show optical activity in pure THF or toluene (negative CD signal at 310 nm), the CD signal disappears on formation of aggregates in good/poor cosolvent systems.     

手性双二茂铁基配体的合成、表征及固体CD光谱

以甲酰基二茂铁(1)和手性1,2-二苯基乙二胺[(1R, 2R)-1,2-二苯基乙二胺(2R), (1S,2S)-1,2-二苯基乙二胺(2S)]为原料, 经缩合、还原和N-烷基化反应, 制备了一对新型手性四齿双二茂铁基配体[N,N’-二(二茂铁基甲基)-N,N’-二(2-羟基丙基)-(1R,2R)-1,2-二苯基乙二胺(5R)和N,N’-二(二茂铁基甲基)-N,N’-二(2-羟基丙基)-(1S,2S)-1,2-二苯基乙二胺(5S)]. 用元素分析、红外(IR)、质子核磁共振(1H NMR)、紫外-可见(UV-Vis)、固体圆二色(CD)光谱等对手性产物(3R-5S)进行了表征. 固体CD光谱研究表明, 配体5R(或5S)的手性特征和4R(或4S)相似而与3R(或3S)却有一定差别.     

Synthesis and crystal structure of a new triosmium alkylidyne carbonyl cluster containing a chiral ferrocenylphosphine ligand

The synthesis, spectroscopic characterization and X-ray crystal structure of a new chiral triosmium alkylidyne carbonyl cluster, (R,S)-[Os3(mu-H)2(CO)9{mu3-CPPh2(eta(5)-C5H4)Fe(eta(5)-C5H3(PPh2)CH(Me)NM(2)}] (1) are described. Compound 1 crystallizes in the non-centrosymmetric space group P2(1) and its absolute configuration has been established.The structure consists of an Os3C metal core with one of the PPh2 moieties of the chiral ferrocenylphosphine bonded to the apical alkylidyne carbon atom to give a zwitterionic cluster complex, reminiscent of the phosphorus ylide.     

Infrared spectrum of matrix isolated selenoformaldehyde, CH2Se, and CD2Se

Thermolysis of highly diluted (CH2Se)3 or (CD2Se)3 in a flow of argon with subsequent quenching of the products in an matrix at 15 K yields monomeric CH2Se and CD2Se, respectively. Six fundamental vibrations upsilon1 = 2972.5, upsilon2 = 1413.3, upsilon3 = 854.2, upsilon4 = 916.4, upsilon 5 = 3052.9, and upsilon 6 = 913.2 cm(-1) and two combination bands have been observed for CH2Se as well as three fundamentals of CD2Se. The vibrational wavenumbers are compared with those of CH2O and CH2S. Matrix isolated selenoformaldehyde decomposes slowly by UV photolysis to yield the CSe molecule.     

Interchromophoric interactions in chiral X-type π-conjugated oligomers: a linear and nonlinear optical study

A concept of chiral, X-type organized π-conjugated oligomers, linked by means of a binaphthalene pincer, is presented. NMR spectroscopy and cyclic and differential pulse voltammetry indicate that these oligomers are in close proximity and influence each other in a through-space manner in their neutral as well as in their oxidized states. The interaction between the oligomers was also confirmed by UV-vis, CD, and emission spectroscopy. The synthetic versatility of this design also enables the development of heterocoupled binaphthalene derivatives BN1-2 and BN1-3, consisting of an electron-neutral oligothiophene or electron-rich oligomer and an electron-poor oligothiazole. Hyper-Rayleigh scattering data show a significant enhancement of the second-order nonlinear hyperpolarizability β for BN1-3 and BN1-2, in contrast with the homocoupled binaphthalene derivatives (BN1-1, BN2-2, and BN3-3). This enhancement provides direct proof for the through-space charge-transfer interaction between the p-type and the n-type oligomers within BN1-3 and BN1-2.     

Synthesis and spectroscopy of anthracene-containing linear and ‘T’-shaped π-conjugated ligands

A range of new π-conjugated ethynyl- and diethynyl-benzene ligands has been synthesised and their spectroscopic characterisation carried out, most notably via IR and ¹H NMR. X-ray crystal structures were obtained for three of these ligands and one unusual ruthenium complex. Both the 4-ethynyl- and 2,5-diethynyl-benzene cores of these compounds have been functionalised through organic transformations by addition of an 9-anthracenyl. This has been attached via a range of linker moieties that vary in both their length and degree of π-conjugation. This has given rise to two groups of compounds with either a linear, e.g., 9-(2-(4-ethynylphenyl)ethynediyl)anthracene and 9-(2-(4-ethynylphenyl)ethyl)anthracene, or ‘T’-shaped morphologies, e.g., 9-(2-(2,5-diethylnylphenyl)ethyl)anthracene.     

Intramolecular vibrational energy redistribution in bridged azulene-anthracene compounds: ballistic energy transport through molecular chains

Intramolecular vibrational energy flow in excited bridged azulene-anthracene compounds is investigated by time-resolved pump-probe laser spectroscopy. The bridges consist of molecular chains and are of the type (CH(2))(m) with m up to 6 as well as (CH(2)OCH(2))(n) (n=1,2) and CH(2)SCH(2). After light absorption into the azulene S(1) band and subsequent fast internal conversion, excited molecules are formed where the vibrational energy is localized at the azulene side. The vibrational energy transfer through the molecular bridge to the anthracene side and, finally, to the surrounding medium is followed by probing the red edge of the azulene S(3) absorption band at 300 nm and/or the anthracene S(1) absorption band at 400 nm. In order to separate the time scales for intramolecular and intermolecular energy transfer, most of the experiments were performed in supercritical xenon where vibrational energy transfer to the bath is comparably slow. The intramolecular equilibration proceeds in two steps. About 15%-20% of the excitation energy leaves the azulene side within a short period of 300 fs. This component accompanies the intramolecular vibrational energy redistribution (IVR) within the azulene chromophore and it is caused by dephasing of normal modes contributing to the initial local excitation of the azulene side and extending over large parts of the molecule. Later, IVR in the whole molecule takes place transferring vibrational energy from the azulene through the bridge to the anthracene side and thereby leading to microcanonical equilibrium. The corresponding time constants tau(IVR) for short bridges increase with the chain length. For longer bridges consisting of more than three elements, however, tau(IVR) is constant at around 4-5 ps. Comparison with molecular dynamics simulations suggests that the coupling of these chains to the two chromophores limits the rate of intramolecular vibrational energy transfer. Inside the bridges the energy transport is essentially ballistic and, therefore, tau(IVR) is independent on the length.     

Syntheses and photophysical studies of cyclodextrin derivatives with two proximate anthracenyl groups

A series of permethylated cyclodextrin derivatives, cyclodextrin dimers doubly bridged with two anthracene moieties (An2CD2) and singly bridged with one (AnCD2) and the monomer bearing two anthracene moieties (An2CD), were newly synthesized. For An2CD2, the two isomeric forms are also identified. All compounds are soluble in both aqueous and various organic solvents. The bisanthracene systems, An2CD2 and An2CD, show the thermal equilibrium in an aqueous solution between the intramolecularly interacting (closed) and less-interacting (open) states of the anthracene moieties, which results in the temperature-dependent absorption changes. These systems also show the characteristic excimer emission that is enhanced in water and weakened in organic solvents. The excitation spectra for the monomer and excimer fluorescence are found to be quite different from each other and similar to the absorption spectra of the open and the closed forms, respectively. The observed unique parallelism between excitation and absorption spectra for the present excimer systems indicates the dual ground state-dual excitation scheme where the excitation state formed from the closed ground state mainly gives excimer. The fluorescence lifetime analyses reveal that the rates of the conversion from the excited state of the open form to that of the closed one (6.0 x 10(6) s(-1) for An2CD2-2) are largely retarded compared with that of the ethyleneoxy linked bisanthracene system (8.8 x 10(7) s(-1)).