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Products of main group elements from cross-coupling reactions have been shown to serve as Lewis acids, mediating further reactions of organic coupling products. Thus, the nickel-catalysed olefination of benzylic dithioacetal with MeMgI in benzene in a sealed Schlenk tube at 130 °C generates magnesium mercaptide which regioselectively converts 2-arylpropene into a dimer in good yield. Aryl iodide reacts with 2-propenylmagnesium bromide in the presence of 1,2-ethanedithiol and NiCl 2 (PPh 3 ) 2 to yield the same dimer. Replacement of the Grignard reagent by an organozinc reagent gives the dimers in a better yield., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

The Grubbs G-I or G-II catalyst gives the ruthenium ethoxy carbene complex, which catalyzes ring-opening cross metathesis (ROCM) of a strained cyclic alkene to give a diene where one of the two alkene moieties in the product contains an ethoxy substituent. No polymeric products are detected. Hydrocarbons such as parent norbornene or substituted cyclopropenes can proceed with the reaction smoothly. Tertiary amines, N -alkylimides, esters, and aryl or alkyl bromides remain intact under the reaction conditions. In addition to vinyl ethers, vinylic esters can also be used. The time required to reach a 50% yield of the ROCM product t 50 varies from 0.01 to 140 h depending on the strain and nucleophilicity of the double bond. Anchimeric participation of an electron-rich group would result in significant enhancement of the reactivity, and the t 50 could be as short as several minutes. A similar substrate without such a neighboring group shows a much slower rate. An exo -norborne derivative reacts much faster than the corresponding endo -isomer. Alkenes with poor nucleophilicity are less favored for the ROCM process, so is less strained cyclooctene.

Bis-norbornene and bis-cyclobutene with different kinds of linkers have been extensively used for the synthesis of double stranded ladderphanes under ruthenium- or molybdenum-catalyzed ring opening metathesis polymerization (ROMP) conditions. The key to the success relies on the selective formation of comb-like polynorbornenes or polycycloubtenes, where pendants are all aligned towards similar direction. This minireview summarizes various methods (chemical methods, spectroscopic means, and nonlinear optical measurements) for determining the comb-like conformations of pendants on these rigid-rod polymers. The approach is based on the proximal relationship between adjacent pendants. Interactions between these adjacent pendants would enable a change in chemical reactivity., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The preparation of linear polysilsesquioxanes having Si-OH side groups is not trivial, because direct condensation of multifunctional silanol derivatives would lead to branched or crosslinked polymers. We have successfully prepared an unsymmetrical double-decker silsesquioxane with a silyl hydride function at one end and two silanol groups at the other. Linear POSS polymers having Si-OH side groups are obtained selectively in good yields. The properties and potential applications are briefly presented.

At 0 °C in THF in the presence of Grubbs first generation catalyst, cyclobutene derivatives undergo ROMP readily, whereas norbornene derivatives remain intact. When the substrate contains both cyclobutene and norbornene moieties, the conditions using THF as the solvent at 0 °C offer a useful protocol for the selective ROMP of cyclobutene to give norbornene-appended polycyclobutene. Unsymmetrical ladderphane having polycyclobutene and polynorbornene as two strands is obtained by further ROMP of the norbornene appended polycyclobutene in the presence of Grubbs first generation catalyst in DCM at ambient temperature. Methanolysis of this unsymmetrical ladderphane gives polycyclobutene methyl ester and insoluble polynorbornene-amide-alcohol. The latter is converted into the corresponding soluble acetate. Both polymers are well characterized by spectroscopic means. No norbornene moiety is found to be incorporated into polycyclobutene strand at all. The double bonds in the polycyclobutene strand are mainly in cis configuration (ca 70%), whereas the E / Z ratio for polynorbornene strand is 8:1.

We used transient absorption and time-correlated single photon counting (TCSPC) techniques to investigate the charge transfer reaction in monosilylene-spaced aminostyrene stilbene monomer. With 266 nm excitation, both stilbene (sti) and aminostyrene (ast) moieties were excited. In nonpolar solvents, the transient absorption band centered at 600 nm appeared promptly and is assigned to the excited state of sti*; this state relaxes at time constant 1.2-1.4 ps and is explained to proceed energy transfer to ast 1ππ*. The second transient band at 460 nm is assigned to absorption of ast 2ππ*; this state accessed from direct excitation has a lifetime 65 ps. This agrees with the observation of 85-89 ps emission decay from the TCSPC measurements. In polar solvent, an excited absorption band centered at 530 nm appeared with a rise time constant 0.2-0.6 ps. This band is assigned to the charge transfer state. This charge transfer process occurs as the acceptor fluorophore (sti) is excited and the electron moves from the occupied π orbital of donor ast to sti* forming ast + sti - . This rise time corresponds to the combined processes of charge and energy transfers. The second rise in this charge-transfer state at time constant 0.74-1.5 ps is observed and assigned to occur from electron hopping from ast 2π* orbital to sti π*. The third time constant 18-31 ps is observed and is attributed to conversion of anti to syn form in the charge-transfer state because the syn form is more polar and further stabilized in polar environment. A rapid charge transfer process in monosilylene-spaced system although two Si-C single bonds are used as spacer is possibly because of the short distance of the ast and the sti conjugated systems, resulting in π orbital overlap between donor and acceptor.

A series of (t)Bu-substituted Z-oligodiacetylenes (Z-ODAs) are synthesized from the reactions of allenyl/propargylic zinc reagents, obtained from the corresponding propargylic dithiolanes and BuLi, with dithiolane-substituted propargylic aldehydes followed by stereospecific elimination of β-thioalkoxy alcohols under Mitsunobu conditions. The stereochemical assignments are based on NOE experiments. The X-ray structure of the hexamer further supports the Z configuration for each of the double bonds in these ODAs. The photophysical properties of these Z-ODAs have been examined and are compared with known related E- and Z-ODAs with different substituents.

Radical-initiated addition of CCl4, Cl3CBr, PhSH, and (TMS)3SiH to (bisisopropyl)silylenedioxy-tethered bis-methacrylate derivatives gives the corresponding eight-membered ring cyclic adducts stereoselectively. Hydrolysis of halo-substituted cyclic adducts with HCl in methanol affords the corresponding valerolactones, and the stereochemistry was determined by the X-ray crystallography on a dibromobenzoate derivative. DFT calculation on the eight-membered radical intermediate offers a plausible rationale for the stereoselectivity of the reaction.

Communication between chromophores is vital for both natural and non-natural photophysical processes. Spatial confinements offer unique conditions to scrutinize such interactions. Polynorbornene- and polycyclobutene-based ladderphanes are ideal model compounds in which all tetraarylethylene (TAE) linkers are aligned coherently. The spans for each of the monomeric units in these ladderphanes are 4.5-5.5 Å. Monomers do not exhibit emission, because bond rotation in TAE can quench the excited-state energy. However, polymers emit at 493 nm (Φ=0.015) with large Stokes shift under ambient conditions and exhibit dual emission at 450 and 493 nm at 150 K. When the temperature is lowered, the emission intensity at 450 nm increases, whereas that at 493 nm decreases. At 100 K, both monomers and polymers emit only at 450 nm. This shorter-wavelength emission arises from the intrinsic emission of TAE chromophore, and the emission at 493 nm could be attributed to the excimer emission in the confined space of ladderphanes. The fast kinetics suggest diffusion-controlled formation of the excimer., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Trimeric oligonorbornenes with hammock-like crown ether pendants 3b and 3c were selectively synthesized by cascade metathetical cyclopolymerization upon treatment with the first generation Grubbs catalyst. These crown-ether-containing oligonorbornenes are impregnated in egg yolk phosphatidylcholine (EYPC) liposome as an artificial ion channel. The efficiency of the sodium ion transport properties has been examined. Oligomer 3c having a polar hydroxy end group exhibits the highest transport efficiency, which is comparable with the best efficiencies reported in literature. The orientation of the crown ether moieties in these oligomers may be critical for the ion transport properties., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A polymeric ladderphane is a step-like structure comprising multiple layers of linkers covalently connected to two or more polymeric backbones. The linkers can be planar aromatic, macrocyclic metal complexes, or three-dimensional organic or organometallic moieties. Structurally, a DNA molecule is a special kind of ladderphane, where the cofacially aligned base-pair pendants are linked through hydrogen bonding. A greater understanding of this class of molecules could help researchers develop new synthetic molecules capable of a similar transfer of chemical information. In this Account, we summarize our studies of the strategy, design, synthesis, characterization, replications, chemical and photophysical properties, and assembly of a range of double-stranded ladderphanes with many fascinating structures. We employed two norbornene moieties fused with N-arylpyrrolidine to connect covalently with a range of relatively rigid linkers. Ring opening metathesis polymerizations (ROMP) of these bis-norbornenes using the first-generation Grubbs ruthenium-benzylidene catalyst produced the corresponding symmetrical double-stranded ladderphanes. The N-arylpyrrolidene moiety in the linker controls the isotactic selectivity and the trans configuration for all double bonds in both single- and double-stranded polynorbornenes. The π-π interactions between these aryl pendants may contribute to the high stereoselectivity in the ROMP of these substrates. We synthesized chiral helical ladderphanes by incorporating asymmetric center(s) in the linkers. Replication protocols and sequential polymerization of a monomer that includes two different polymerizable groups offer methods for producing unsymmetical ladderphanes. These routes furnish template synthesis of daughter polymers with well-controlled chain lengths and polydispersities. The linkers in these ladderphanes are well aligned in the center along the longitudinal axis of the polymer. Fluorescence quenching, excimer formation, or Soret band splitting experiments suggest that strong interactions take place between the linkers. The antiferromagnetism of the oxidized ferrocene-based ladderphanes further indicates strong coupling between linkers in these ladderphanes. These polynorbornene-based ladderphanes can easily aggregate to form a two-dimensional, highly ordered array on the graphite surface with areas that can reach the submicrometer range. These morphological patterns result from interactions between vinyl and styryl end groups via π-π stacking along the longitudinal axis of the polymer and van der Waals interaction between backbones of polymers. Such assembly orients planar arene moieties cofacially, and polynorbornene backbones insulate each linear array of arenes from the adjacent arrays. Dihydroxylation converts the double bonds in polynorbornene backbones of ladderphanes into more hydrophilic polyols. Hydrogen bonding between these polyol molecules leads to self-assembly and produces structures with longitudinally staggered morphologies on the graphite surface.

Three double stranded polymeric ladderphanes with 16-π-electron antiaromatic metallocycle linkers are synthesised by ring opening metathesis polymerisation of the corresponding bisnorbornene monomers. Scanning tunnelling microscopic (STM) images indicate that these polymers can assemble nicely on a graphite surface to form a highly ordered pattern which has been observed in other ladderphanes with different kinds of aromatic linkers. Little change in (1)H NMR, absorption spectra and electrochemical oxidation potential between these polymers and the corresponding monomers suggest that there would be no interactions between adjacent antiaromatic linkers in these polymeric ladderphanes. Presumably, the distance between two antiaromatic rings in these ladderphanes (5-6 Å) is far too long in comparison with that between two rings in methylene-bridged antiaromatic superphanes (2.5 Å<), where stabilisation is predicted by theoretical calculations.

A series of oligmers with donor-acceptor pairs separated by diisopropylsilylene (iPr(2)Si) spacers, composed of monomer 4b, dimer 5, trimer 6, and tetramer 7, were synthesized to scrutinize the folding behavior. Monomer 4a with a dimethylsilylene (Me(2)Si) spacer was also prepared for comparison. The 4-aminostyrene moiety was used as the donor and the stilbene moiety as the acceptor. Both steady-state and time-resolved fluorescence spectroscopic measurement were made. Regardless of the substituents on the silicon atom, the emission spectra of 4a and 4b exhibit both local excited (LE) emission of the acceptor chromophore and emission from the charge-separated state (CT emission), which are similar to that of the corresponding Me(2)Si-spaced copolymer 2a with the same donor and acceptor chromophores, but different from that of the copolymer with the iPr(2)Si spacer 2b. Dimer 5 behaves like 4 and 2a. As the chain length of the oligomers increases, the emission properties of the higher homologues become prone to that of 2b. Thus, tetramer 7 exhibits emission from the charge-transfer complex, which is essentially same as that of 2b. Moreover, charge-transfer absorptions emerge in 6 and 7. These results suggest that the folding nature of oligomers approaches that of the corresponding polymer, as the degree of oligomerization increases, and the electronic interactions between adjacent donor-acceptor pairs are controlled by the steric effect of the substituents on the silicon atoms and concomitant amplification of the stabilizing energy by extending the distance of the folding structure., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A series of dialkylsilylene-spaced copolymers 6 and 7, which contain Me(2)Si and iPr(2)Si spacer groups, respectively, and have alternating donor and acceptor chromophores, have been designed and regioselectively synthesized by hydrosilylation. The ratio of the donor and acceptor chromophores for each repeat unit is 2:1, and the two donor chromophores are linked by a trimethylene bridge. A 4-aminostyrene moiety is used as the donor and a series of acceptor chromophores with different reduction potentials are employed. Both steady-state and kinetic measurements reveal that the photoinduced electron transfer (PET) in 6 obeyed the Marcus theory in which normal and inverted regions are observed. On the other hand, the iPr(2)Si-spaced copolymers 7 exhibit absorption and emission from the charge-transfer complexes exclusively due to ground-state interactions between the donor and acceptor chromophores. The discrepancy in photophysical behavior may have arisen from the difference in distance between the adjacent donor and acceptor chromophores. The bulkiness of the substituents on the silicon atom (i.e., Me versus iPr) may exert the Thorpe-Ingold effect on the local conformation around the silicon atom. The differences in the small energetic barriers for each of the conformational states may be amplified by extending the distance of the folding structure, which results in perturbing the conformation of the polymers. These results suggest that the electronic interactions between adjacent donor-acceptor pairs in these copolymers are controlled by the synchronization of the substitution effect and corresponding polymeric structures., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Zinc-porphyrin-appended norbornene derivative 6, the corresponding dimer 7, coherently aligned single-stranded polynorbornene 5, and zinc-porphyrin-linked double-stranded polymeric ladderphane 3 have been used for complexation with 1,4-diazabicyclo[2.2.2]octane (DABCO) to generate an array of porphyrin-DABCO supramolecular scaffolds. The stoichiometries of the complex formation are analyzed in detail by (1)H NMR spectroscopy as well as absorption and emission spectroscopic methods. Bidentate ligand DABCO is found to form with 7, 5, and 3 to give 2-to-1 porphyrin-DABCO sandwich structures. Monomer 6, on the other hand, forms a 2-to-1 porphyrin-DABCO sandwich structure at high concentration (20 mM), but a 1-to-1 porphyrin-DABCO complex at low concentration (10(-6) M). Time-resolved fluorescence decays revealed a similar behavior for the 2-to-1 porphyrin-DABCO sandwich structures that are formed from 3, 5, and 7., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Recent advances in the use of the concept of the Thorpe-Ingold effect to rationalise some synthetic chemistry involving organosilicon compounds and, in particular, the photophysical properties of certain dialkylsilylene spaced conjugated chromophores are discussed. The silicon moieties are considered to be insulating tetrahedral spacers in these silicon-containing copolymers. The substituents on silicon can readily be tuned and the steric environment of these substituents around the silicon may dictate the conformation (or helicity) of the copolymers and hence their photophysical properties. This substituent effect on silicon can be understood by the concept of the Thorpe-Ingold effect.

Two phenanthrene-fused furan-containing teraryl cyclophenes 5 and 6 are synthesized. These cyclophenes exhibit charge transfer band in the absorption spectra, unusually large Stokes shifts in the emission spectra, and exceptionally high mubeta values in the electric-field-induced second-harmonic generation (EFISH) experiments. The mubeta(1.91) values for 5 and 6 are 438 and 777 x 10(-48) esu, respectively. The bridging double bond in 5 and 6 can serve as either an electron donor or acceptor depending on the nature of the substituent on furan rings. DFT calculations at the B3LYP/6-31G** level indicate that the electron density distributions in HOMO and LUMO are very different. Interaction between the oligoaryl systems and the double bond may account for the significant enhancement in hyperpolarizability.

Polynorbornenes appended with porphyrins containing a range of different linkers are synthesized. The use of bisamidic chiral alanine linkers between the pending porphyrins and the polymeric backbone has been shown to bring the adjacent porphyrin chromophores to more suitable orientation for exciton coupling owing to hydrogen bonding between the adjacent linkers. The hydrogen bonding between the adjacent pendants in these polymers may induce a cooperative effect and therefore render single-handed helical structures for these polymers. Such a cooperative effect is reflected in the enhancement of FRET efficiencies between zinc-porphyrin and free base porphyrin in random copolymers.

Centrosymmetric furan-containing cyclophandienes 3 and 4, synthesized by our furan annulation protocol, have been shown to exhibit extraordinarily large Stokes shifts and second-order nonlinear optical beta values. The beta values for 3 and 4 measured at 1.32 mum are 208 and 530x10(-30) esu, respectively. The beta values of 3 and 4 are similar to those of respective cyclophenes 1 a and 7 in which strong hyperpoarizable interactions between two twisted pi-systems (oligoaryl and bridging double bond) might take place. Symmetry breaking due to the resonance contribution (cf. 2) and the unique structural features of 3 and 4 has been used to account for this unusual photophysical behavior.

Self-assembly at the molecular level in solutions or on a surface is a subject of current interest. Herein we describe the tailoring of oligobisnorbornene 1, which represents an innovative concept of a preorganized building block on the tens of nanometer scale. The rodlike 1 has vinyl and styrenyl end groups. Scanning tunneling microscopy (STM) reveals that the oligomers aggregate anisotropically along the long axis and form a one-dimensional assembly in which, remarkably, no interstitial gap appears between neighboring oligomers. Dynamic light-scattering (DLS) measurements indicate that the assembly develops in solution. With a shear treatment for dropcast films, a unidirectionally ordered domain with a defect density less than 0.5 % can be prepared. Simulation results by molecular dynamics suggest that there may be multiple interactions such as pi-pi stacking and dipolar attractions taking place between the termini of the oligomers. To demonstrate the importance of double bonds in the oligomeric backbones and termini towards the tectonic assembly, a hydrogenated analogue was synthesized; pi-pi interactions are thus less significant and the film morphology is completely different from that of 1. This work extends the concept of molecular tectonics to preorganized oligomers and opens up a new avenue of nanopatterning toward nanodevices.

A new class of polymers, which have a double-stranded polybinorbornene skeleton with multilayer planar oligoaryl linkers, defined as polymeric ladderphanes, are synthesized. The structures of these ladderphanes are determined by spectroscopic means. Photophysical studies and time-resolved fluorescence spectroscopic investigations reveal that there is a strong interaction between the chromophore linkers. Thus, Soret band splitting in the absorption spectrum of the polymer with porphyrin linker (12e), significant fluorescence quenching with oligoaryl linkers (12b-d), and excimer emission with a terphenylene-diethynylene linker (12a) are characteristic photophysical properties of these polymers. Scanning tunneling microscopy shows that polymers 12b and d exhibit a ladder-like morphology and form a supramolecular assembly leading to a two-dimensional ordered array on a highly oriented pyrolytic graphite surface.

Six different kinds of coherently aligned porphyrin-appended polynorbornenes derived from 5,6-endo-fused N-arylpyrrolidenonorbornenes have been synthesized. Pi-pi interactions between the pendant groups are essential for dictating the photophysical properties of the polymers and the mechanism for the stereoselective formation of polymers. Splitting of the Soret band of polymers 2a-c, which have alkyl-substituted porphyrin pendant groups, suggests strong exciton coupling between chromophores. No splitting of the Soret band is observed for polymers 2d-f, which have tetraaryl substituents on the porphyrin moiety. Significant fluorescence quenching is found in polymers 2a-e, whereas only slightly reduced quantum yield is observed for 2f. Time-resolved fluorescence measurements also indicate a similar trend. The AFM image of 2d on graphite shows aggregation to form a two-dimensional, ordered pattern.

The relaxation dynamics of excited electronic states of [(1,1'-biphenyl)-4,4'-diyldi-2,1-ethenediyl]bis(dimethylsilane) dissolved in various solvents with varied polarity and viscosity have been investigated. Upon excitation at wavelength 266 nm, we measured the fluorescence curves that exhibit a rise time constant approximately 100 fs, and two decay time constants, 7-65 ps and approximately 1 ns. We attribute the former decay to upper excited states to the S(1) state, and the latter decay to geometric relaxation and the lifetime of the S(1) state. Only the tens of picosecond decay shows a dependence on the solvent viscosity, indicating that the torsional motion dominates the relaxation. Theoretical calculations were performed to obtain the optimized structures of the free [(1,1'-biphenyl)-4,4'-diyldi-2,1-ethenediyl]bis(dimethylsilane) molecule in its ground and first excited states with methods B3LYP/6-311G(d) and CIS/6-311G(d), respectively. The results of these calculations show that the dihedral angle between the two phenyl rings is approximately 34 degrees for trans and approximately 38 degrees for cis conformers in the ground state and that the first excited state has a planar structure, in agreement with the experimental results that indicate that the torsional motion of two phenyl groups elevates the relaxation of the S(1) state. Enhanced vibrational relaxation of S(1) in alcoholic solvents is observed. Rapid relaxation in methanol-OH compared with that in methanol-OD is explained by the excess energy dissipated efficiently through high-frequency vibrational mode (>500 cm(-1)).

Helical double stranded polymers incorporated with a covalently bound chiral ferrocene linker are synthesised and characterized by CD spectra and STM images and molecular dynamics simulations.

Treatment of propargylic dithiolanes 1 with (n)BuLi followed by a carbonyl electrophile yields the corresponding homopropargylic alcohol 3. Upon treatment with 2 equiv of PPh3 and DIAD, elimination of SR and OH moieties from 3 affords the corresponding olefins 4 in moderate to good yield. The reaction can be considered an alternative of McMurry coupling of two different carbonyl equivalents.

Seventy percent of the ferrocene moieties in double-stranded polybisnorbornenes containing linearly aligned ferrocene linkers are oxidised and each of the neighbouring monomeric units in these polymers may strongly interact with each other; the oxidised form of has been shown to be antiferromagnetic.

The concept of the Thorpe-Ingold effect has been used to rationalize the helicity of the silylene-spaced divinylarene copolymers having chiral substituents. Diisopropylsilylene-spaced divinylbenzene copolymers having chiral 2-methylbutoxy substituents have been shown to exhibit a helical conformation. The presence of the bulky isopropyl substituents on silicon would render each of the monomeric units in these copolymers to favor a syn-syn conformation. The copolymer would thus be more folded to form helical morphology as revealed by the notable enhancement of the circular dichroic intensity. The reversible temperature-dependent circular dichroism (CD) profiles further support the stable helical conformation for the copolymers 4 b and 5 b.

A convenient protocol to fabricate an organic-inorganic hybrid system with covalently bound light-harvesting chromophores (stilbene and terphenylene-divinylene) and an electron acceptor (titanium oxide) is described. Efficient energy- and electron-transfer processes may take place in these systems. Covalent bonding between the acceptor chromophores and the titania/silica matrix would be important for electron transfer, whereas fluorescence resonant energy transfer (FRET) would strongly depend on the ratio of donor to acceptor chromophores. Time-resolved spectroscopy was employed to elucidate the detailed photophysical processes. The coupling of FRET and electron transfer was shown to work coherently to lead to photocurrent enhancement. The photocurrent responses reached a maximum when the hybrid-material thin film contained 60 % acceptor and 40 % donor.

Electrochemical oxidation of pentaaryl 2 containing two furan moieties occurs sequentially to give diketone 8 after two-electron transfer. Further oxidation with another two-electron transfer gives the corresponding tetraketone 9. Radical cation intermediate is detected by absorption spectroscopy. The radical intermediates of different regiochemistry have been shown to exhibit different oxidation potentials as revealed by the differential pulse voltammetry.

Geminal disubstitution on silicon in dialkylsilylene-spaced divinylarene copolymers may dictate the conformation and photophysical properties of the copolymers, bulky (i)Pr substituted copolymers being more folded than Me substituent analogues.

Treatment of propargylic dithiolanes with nBuLi followed by a carbonyl electrophile yields the corresponding propargylic dithioacetals. Upon treatment with 1 equiv of Fe(acac)3 and excess MeMgI, elimination of SR and OH moieties from 8 affords the corresponding olefins in satisfactory yield. Benzylic dithioacetals behave similarly. The reaction can be considered an alternative of McMurry coupling of two different carbonyl equivalents.

Measurements of molecular break junction reveal quantitatively the correlation between the single-molecule conductance and the conformation of pi-conjugated molecules with 6-18 conjugated double bonds.

Two dimers and a series of polymers with 5,6-endo pendant aryl groups that contain different substituents at the para positions were synthesized. The conformation and stereochemistry of the dimers and polymers were determined by nonlinear optical analysis (EFISH) as well as UV/Vis and 13C NMR spectroscopy. The chemical shifts of C7 for the polymers appeared as two peaks in the 13C NMR spectra when the substituents are electron-withdrawing groups. The percentage decrease in the relative extinction coefficient of the polymers, epsilon(d), was linearly related to the Hammett constant sigma. Polynorbornenes with electron-withdrawing substituents may adopt isotactic stereochemistry with all pendant groups aligned in one direction. The nature of the interactions between neighboring chromophores may be one of the most important factors in directing the stereoregularity and conformation of these polymers. The corresponding polymers derived from the exo isomers appeared to be less stereoregular.

A summary of recent advances on the chemistry and photophysics of silylene-spaced divinylarene copolymers is presented. The silicon moieties have been shown to serve as an insulating spacer in these copolymers. The photophysical studies have provided useful insights into how chromophores in polymers interact intramolecularly. Because different chromophores can be regioregularly introduced into the polymeric chain, these copolymers have been extensively used as models for studying energy transfer, light harvesting as well as chiroptical transfer.

A range of oligoaryls that contain alternating benzene-furan rings is synthesized by a rapid convergent/divergent method from the annulation of a propargylic dithioacetal and an aldehyde with a propargylic dithioacetal moiety as a substituent. These oligomers are fairly soluble in a range of organic solvents and can be easily purified by reprecipitation. The substituents on the furan rings can be varied according to the substituents in the starting propargylic dithioacetals. This route provides a useful procedure for the synthesis of alternating benzene-furan oligomers without repeated units. These furan-containing oligoaryls are highly fluorescent in the visible region and are electrochemically active. The band gaps of these oligomers appear to be less sensitive towards changes in conjugation length than those of oligofurans.

A range of polynorbornenes (PNBs) with fused dipolar pendant groups at C-5,6 positions was synthesized by ring-opening metathesis polymerization catalyzed by a ruthenium carbene complex (Grubbs I). Photophysical studies, EFISH measurements, and atomic force microscopy images have been used to investigate the structures and morphology of these polymers. These results suggest that the polymers may adopt rigid rod-like structures. The presence of the double bonds in PNBs appeared to be indispensable for the rigidity of the polymers. Interaction between unsaturated pendant groups may result in coherent alignment leading to a rod-like structure.

Thin films of silica hybrid materials consisting of two to three covalently bound organic chromophores at different ratios were conveniently synthesized and fabricated. The photophysical properties of these materials have been studied. The fluorescence spectra reveal complete fluorescence resonance energy transfer (FRET) from donor to acceptor, and the light-harvesting ability of these hybrid materials increases with increasing the molar fraction of donor chromophore. In a three-chromophore system, the energy is transferred from 300 to 530 nm successfully. Time-resolved fluorescence experiments are employed to elucidate the average rates and efficiencies (84-97%) of energy transfer in these organic/inorganic hybrid systems. The hybrid materials have been shown to provide antenna effect to facilitate energy transfer and light harvesting.

The mechanisms involved in the apoptotic effect of LCY-2-CHO [9-(2-chlorobenzyl)-9H-carbazole-3-carbaldehyde], a synthetic carbazole derivative identified as an anti-inflammatory compound, were studied. Cell cycle analysis by propidium iodide staining in human THP-1 monocytic leukemia cells showed the ability of LCY-2-CHO to increase cell population in sub-G1 stage with time- and concentration-dependent manners. LCY-2-CHO-mediated cell death was also demonstrated by DNA laddering and was not related to the release of lactate dehydrogenase. Apoptosis in THP-1 cells induced by LCY-2-CHO was accompanied by the Bid cleavage, collapse of mitochondrial transmembrane potential, the release of cytochrome c and the activation of caspase-3. The apoptotic effect of LCY-2-CHO was diminished by the presence of zVEID-fmk (caspase-6 inhibitor), zIETD-fmk (caspase-8 inhibitor), and zVAD-fmk (non-selective caspase inhibitor), but was not altered by several antioxidants, and cathepsin inhibitor. The Bid cleavage and loss of mitochondrial transmembrane potential, but not the cytochrome c release, were reversed by zIETD-fmk. Comparing the cell selectivity of LCY-2-CHO, we found T-cell acute lymphoblastic CEM leukemia cells were sensitive to 1 microM LCY-2-CHO, acute myeloid leukemia HL-60 cells underwent apoptosis at 10 microM, while adherent cancer cells, such as PC3, HT29 and MCF-7, were resistant to 30 microM LCY-2-CHO within 24-h incubation. Taken together in the present study, we demonstrated LCY-2-CHO might be apoptotic for malignant hematopoietic cells but not anchorage-dependent cells. This action is mediated by an intrinsic caspase-dependent apoptotic event involving mitochondria.

We demonstrated that mono- and dithiolated furan-containing oligoaryls (II-IV, see Chart 2) can be successfully synthesized via a one-pot strategy starting from propargylic dithioacetals. IRAS (infrared reflection-absorption spectroscopy) and STM (scanning tunneling microscopy) experiments revealed that single-component monolayers of II, III, and IV are essentially disordered, an important property that prevents excited photoluminescent molecules from self-quenching in the organic layers of an OLED device. Surprisingly, localized lattice packing of crystalline dithiolated furan oligoaryls on Au(111) can be assembled by immersing preadsorbed n-dodecanethiol SAMs in the corresponding deposition solutions. The discrepancy in the formation of disordered or localized crystalline structures is discussed. For single-component monolayers, the facile formation of S-Au bonds generates chaotically distributed monolayers in which the arched molecules hinge each other and block the desorptive pathways. The absence of crystalline packing is mainly attributed to the difficulty for the dithiols to simultaneously break two S-Au bonds, to desorb, and then to readsorb, the key step to improve the intermolecular attractions for crystalline SAMs. By preassembling n-dodecanethiol SAMs, the space for dithiolated compounds III and IV to adsorb is limited to domain boundaries or packing defects where crystalline packing of III and IV can grow.

A series of silylene-spaced alternating [(donor-SiMe2)(n=1-3)-(acceptor-SiMe2)] copolymers 4-6 was synthesized by rhodium-catalyzed hydrosilylation of bisalkynes with bissilyl hydrides. Monomeric reference compounds 7-10 with similar chromophore components were prepared for comparison. The ratio of donor to acceptor groups is well-controlled by the precise regiochemistry and nature of the repeat units. The silylene moieties serve as insulating spacers between chromophores. The polymers exhibit light-harvesting abilities, for which the intensity of the emission enhanced with larger donor-to-acceptor ratios. No emission originating from the donors was observed in fluorescence spectra, illustrating that intrachain energy transfer is highly efficient along the polymer chain.

[reaction: see text] Pd(2)(dba)(3)-Ph(3)P-catalyzed Kumada-Corriu coupling reactions of unactivated alkyl bromides or iodides with an alkynyl nucleophile furnish C(sp)-C(sp)3 bond formation. Alkynyl nucleophiles can be alkynyllithiums or the corresponding Grignard reagents. The superior performance of Ph(3)P ligand over the trialkylphosphine ligands indicates that this cross-coupling reaction may be a reductive-elimination-controlled process.

The effects of carboxyfullerene on a well-known neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its active metabolite 1-methyl-4-phenyl-pyridinium (MPP+) were investigated. In chloral hydrate-anesthetized rats, cytosolic cytochrome c was elevated in the infused substantia nigra 4 h after an intranigral infusion of MPP+. Five days after local application of MPP+, lipid peroxidation (LP) was elevated in the infused substantia nigra. Furthermore, dopamine content and tyrosine hydroxylase (TH)-positive axons were reduced in the ipsilateral striatum. Concomitant intranigral infusion of carboxyfullerene abolished the elevation in cytochrome c and oxidative injuries induced by MPP+. In contrast, systemic application of carboxyfullerene did not prevent neurotoxicity induced by intraperitoneal injection of MPTP. In mice, systemic administration of MPTP induced a dose-dependent depletion in striatal dopamine content. Simultaneous injection of carboxyfullerene (10 mg/kg) actually potentiated MPTP-induced reduction in striatal dopamine content. Furthermore, systemic administration of carboxyfullerene (30 mg/kg) caused death in the MPTP-treated mice. An increase in the striatal MPP+ level and reduction in hepatic P450 level were observed in the carboxyfullerene co-treated mice. These data showed that systemic application of carboxyfullerene appears to potentiate MPTP-induced neurotoxicity while local carboxyfullerene has been suggested as a neuroprotective agent. Furthermore, an increase in striatal MPP+ level may contribute to the potentiation by carboxyfullerene of MPTP-induced neurotoxicity.

The phosphine-containing polymer 1 is obtained by ruthenium-catalyzed ring-opening metathesis polymerization of the norbornene derivative 2. Polymer 1 is employed as the polymer support in the palladium-catalyzed Heck, Sonogashira, and Negishi reactions, and the corresponding (methoxymethylphenyl)diphenylphosphine (6) ligand is used for comparison. The polymer-supported catalysts retain most of their catalytic activities in these coupling reactions in the recycling processes.

[reaction: see text] Olefination of aliphatic dithioacetals with Grignard reagents is catalyzed by Ni(acac)(2) in the presence of an appropriate trialkylphosphine ligand.