We report the synthesis of a series of crystalline acenedithiophenes with up to seven linearly fused rings and silylethynyl substituents. These functional groups are designed to both improve solubility and enhance cofacial interactions in the solid. We discuss the crystal packing of these materials, as well as their physical properties such as oxidation potential, UV−vis absorption, fluorescence emission, and decomposition pathways.

As part of our program investigating the use of ethynylated acenes in organic electronics, we have prepared a series of functionalized tetracene derivatives in search of a material with red emission suitable for use in display technologies. A number of such compounds with functionalization on the alkyne and/or the acene ring were easily prepared in one or two steps from commercially available materials. Solution fluorescence quantum efficiencies were generally good for these derivatives, which possessed emission maxima spanning the range 540−637 nm. Simple light-emitting diodes fabricated from these compounds showed that one of the derivatives did exhibit red electroluminescence.

Polymeric materials exhibit an extraordinary range of mechanical responses ), which depend on the chemical and physical structure of the polymer chains. 3 Polymers are broadly categorized as thermoplastic, thermoset, or elastomer. Thermoplastic polymers consist of linear or branched chains and can be amorphous or semicrystalline. The mechanical response of thermoplastic polymers is highly influenced by the molecular mass, chain entanglements, chain alignment, and degree of crystallinity. Thermosetting polymers consist of highly cross-linked three-dimensional networks. The mechanical properties of these amorphous polymers depend on the molecular mass and the cross-link density. Elastomers (e.g., rubber) are highly deformable elastic networks that are lightly cross-linked by chemical or physical junctions.

Mechanochemistry is the study of force-induced scission of covalent bonds. 1 Selective force-induced bond scission has been demonstrated in a variety of chemical moieties called mechanophores. 2a-i Solution sonication studies and mechanical analysis of solid polymers has allowed for the identification of these inherently reactive molecular structures. Although several mechanophores have been identified, few examples have produced reactive species that can be utilized for self-healing applications. Here we demonstrate the mechanically-induced generation of reactive alkenes upon fragmentation of a strained dicyano-substituted cyclobutane ring (polymer 1, Scheme 1A), which cleaves faster and more selectively than a control (polymer 2, Scheme 1B). Trapping experiments with a Michael donor are consistent with of a formal retro [2 + 2] cleavage of 1, yielding cyanoacrylate functional groups. Since cyanoacrylates are known to readily undergo addition reactions under mildly basic conditions, it may be possible to incorporate this mechanophore into solid polymers that selectively react and autonomically repair themselves upon application of mechanical force.

A series of 1,7-bis(arylethynyl)-N,N′-bis[2,6-diisopropylphenyl]perylene-3,4:9,10-bis(dicarboximide)s has been obtained from Sonogashira coupling of the 1,7-dibromoperylene-3,4:9,10-bis(dicarboximide) with p-substituted phenylacetylenes in which the p-substituents include π-donors (dialkylamino, diarylamino, p-(diarylamino)phenyl, alkoxy) and π-acceptors (diarylboryl, p-(diarylboryl)phenyl). The bis(arylethynyl)-substituted chromophores all show two reversible molecular reductions and are all slightly more readily reduced than unsubstituted perylene-3,4:9,10-bis(dicarboximide)s with the electrochemical potentials being rather insensitive to the π-donor or acceptor nature of the aryl group. The amine derivatives also show reversible molecular oxidations. The UV-vis spectra of the chromophores with alkoxy and boryl substituents show red-shifted absorptions relative to unsubstituted perylene diimides with discernible vibronic structure. In contrast, the lowest energy absorptions of the amino derivatives are broad and structureless, suggesting donor-to-acceptor charge-transfer character. Transient absorption spectra for the amine derivatives were interpreted in terms of ultrafast charge separation, followed by charge recombination on a time scale of ca. 80-2000 ps. Two compounds were also synthesized in which an additional stronger, but more weakly coupled, donor group is linked by a nonconjugated bridge to the p-amine donor, to investigate the effect on the charge recombination lifetimes; however, the lifetimes of the charge-separated states, ca. 150 and 1000 ps, were within the range observed for the simple amine systems. Finally, the two-photon absorption properties of three bis(arylethynyl)substituted derivatives were investigated, along with those of 1,7-di(pyrrolidin-1-yl)-N,N′-bis[2,6-diisopropylphenyl]perylene-3,4:9,10-bis(dicarboximide). As with other perylene-3,4:9,10-bis(dicarboximide)s and related species, strong two-photon absorption (>1000 GM) was observed for three of these species close to the one-photon absorption edge; however, an additional feature (100-500 GM) was also observed at longer wavelength. An example with (p-aminophenyl)ethylnyl substituents showed a qualitatively different twophoton spectrum with a cross-section >500 GM being observed over a broad wavelength range. Figure 1. Generic structure of a PDI including two structures compared with the alkyne derivatives discussed in this paper.

We report the synthesis, electrochemistry, and photophysical properties of a new donor-acceptor-donor molecule in which the meso carbon atoms of two zinc porphyrin (POR) units are linked through ethynylene bridges to the 1,7-positions of a central perylene-3,4:9,10-bis(dicarboximide) (PDI). In contrast to previously studied systems incorporating POR and PDI groups, this alkyne-based derivative shows evidence of throughbond electronic coupling in the ground state; the new chromophore exhibits absorption features similar to those of its constituent parts as well as lower energy features (at wavelengths up to ca. 1000 nm), presumably arising from donor-acceptor interactions. Transient absorption measurements show that excitation at several visible and near-IR wavelengths results in the formation of an excited-state species with a lifetime of 290 ps in 1% (v/v) pyridine in toluene. The absorption spectrum of this species resembles the sum of the spectra for the chemically generated radical cation and radical anion of the chromophore. The chromophore shows moderate two-photon absorption cross sections (2000-7000 GM) at photon wavelengths close to the onset of its lowenergy one-photon absorption feature.

A number of processing variations were carried out to optimize the morphology, thirdorder nonlinearity, and processability of substituted polyacetylene polymers. This allowed for spin coating of optical quality films with large nonlinearities.

Nitrogen-containing multiwalled nanotubes (N-MWCNTs), formed by CVD from a nitrogen-containing feedstock have a 'bamboo' structure in which the axes of the graphene planes are not parallel to the axis of the nanotube and the core is periodically bridged. We find that thermal and chemical treatment of these materials can produce nanotubes that have been cut longitudinally in either a linear or in a spiral manner. In addition, these longitudinally cut nanotubes can be partially or fully unrolled by sonication in an aqueous surfactant, producing graphite platelets as well as narrow structures that could be thin graphite ribbons or very narrow, intact N-MWCNTs. These different morphologies of graphite, available from one source, suggest that there are multiple structures of N-MWCNTs present, few as simple as stacked cups or nested scrolls.

The reaction mixture was stirred at 50-60 OC for 4 h. The homogeneous dark yellow brown solution was filtered through a Celite layer and the volatiles were removed in vacuo. The residue was redissolved at 50-60 OC in ca. 50 mL of toluene. Hexane was added until a beginning cloudiness remained, and the solution was slowly cooled, first to room temperature and then to 5 OC. The dark yellow crystals formed were isolated by Schlenk filtration, washed with hexane, dried in vacuo, and kept under argon.

The crystal structure of 7,8-(dichloromethano)homo [70]fullerene shows that addition of the dichlorocarbene ( : CCl 2 ) to C 70 gives a surprisingly normal methano-bridged [9]annulene. The structural changes caused by the addition are highly localized; the C(7)ÀC(8) distance lengthens by 0.705(2) ä but no other distance changes by more than 0.022(3) ä. Bond angles within the [9]annulene increase by as much as 7.8(1)8, but changes outside the C 9 ring are much smaller. The nearly ellipsoidal molecules form hexagonally close-packed layers that interact in pairs through short Cl ¥¥¥ C, and possibly short Cl ¥¥¥ Cl and C ¥¥¥ C, interactions.

Reduction reactions of molybdate in acidic, aqueous solution lead to colored, mixed-valent Mo V/VI polyoxomolybdate (POM) species. The two-century-old mystery of the "molybdenum blues" 6 exemplifies the difficulty in characterizing suspensions of POM particles. Müller, Liu, and co-workers revealed the fundamental compositions of the related "molybdenum browns", including I h symmetrical keplerates. In general, reduced molybdates assemble into nanometric species . Light-scattering, small-angle X-ray scattering (SAXS), and microscopy show slow aggregation of Na 15 [Mo VI 126 -Mo V 28 O 462 H 14 (H 2 O) 70 ] 0.5 -[Mo VI 124 Mo V 28 O 457 H 14 (H 2 O) 68 ] 0.5 ‚ca.‚ 400 H 2 O. 7,8 and neutral [{(Mo VI (Mo VI 5 O 21 )(H 2 O) 6 } 12 {Fe III (H 2 O) 6 } 30 ]‚ ca.‚150 H 2 O. 9,10 Formation of POM nanostructures in the presence of polymers and surfactants has also been reported. 11-14 We report here a combination of physical methods that allows us to monitor the dynamics of the size distribution and the chemical nature of suspended POM particles derived from {Mo 132 } keplerate in situ. The {Mo 132 } system is well suited for this investigation. Partial reduction of (NH 4 ) 6 Mo 7 O 24 ‚4H 2 O with N 2 H 4 ‚H 2 SO 4 in CH 3 CO 2 -NH 4 /CH 3 CO 2 H buffer produces crystals of (NH 4 ) 42 [Mo VI 72 -Mo V 60 O 372 (CH 3 CO 2 ) 30 (H 2 O) 72 ]‚ca.‚300H 2 O‚ca.‚10 CH 3 CO 2 NH 4 . The {Mo 132 } keplerate anion is I h symmetrical with charge -42 and diameter ca. 2.9 nm. 5,15,16 Light-scattering methods are hindered by the deep color of the {Mo 132 } suspension, although Liu and co-workers were able to use scattering methods to study aggregation in lighter colored 10,14,17 {Mo 154 } 8 and MoO 3 /triblock copolymers. 12,13 Although Müller and co-workers have studied surfactant-encapsulated {Mo 132 } 11 and oxidized {Mo 132 } species 18,19 and Cammers et al. have kinetically coprecipitated {Mo 132 } with tripodal hexaminetriscrown ethers, 20 the evolution of nanometer species of an unperturbed {Mo 132 }-derived suspension is uninvestigated.

Addition of benzyne to C 70 results in four isomeric monoadducts (compounds 1a-d) in a 42:35: 13:10 ratio as determined by 1 H NMR. These compounds were separated by repeated passes through HPLC columns. The major isomer (1a) resulted from addition to the highly pyramidalized C1-C2 bond as shown by 13 C NMR and UV/vis spectroscopy. The structure of the C1-C2 adduct (1a) was confirmed by X-ray crystallography. The second isomer (1b) was assigned as an adduct to the C5-C6 bond on the basis of 13 C NMR and UV/vis spectroscopy. Compound 1c exhibited a 13 C spectrum consistent with an adduct to the C7 and C8 positions. The presence of sp 3 13 C NMR resonances proved that the C7-C8 bond is still intact, making this the first identification of direct addition to a 5-6 ring fusion in a fullerene, and the first example of an adduct to a 5-6 ring fusion where the ring fusion bond remains intact. The fourth isomer (1d) displayed spectral data consistent with a compound with C 1 symmetry and is assigned as an adduct to the C7-C21 bond.

Purification of single-walled carbon nanotubes by capillary electrophoresis (CE) is demonstrated. Real-time Raman spectroscopy of the separation process and single-wavelength UV/vis detection show the ability of CE to provide high-resolution separations of nanotube fractions with baseline separation. AFM images of collected fractions demonstrate that separations are based on tube length. The separation method is suggested to be based on alignment of the nanotubes along the separation field.

H2 remains preferentially in the same plane as the bond with a small rotational barrier of 3 kcal/mol. Remarkably the interaction between the metal d orbitals and u *~~ is similar for the in-plane and out-of-plane orientation of H2. The preference for a coplanar arrangement can be traced to a cis interaction between the Ru-H u bond and the u * H H orbital (4). This interaction is also responsible for the fact that the Ru-H is bent toward the H2 ligand. As has been previously shown in an Fe-(II)-H/Hz complex,4a this interaction creates a nascent bond between the hydride and the closest H center of H2. This nascent bond should facilitate the exchange process between the hydrogens. I 4 A possible path for exchanging the H centers is shown in 5 (perpendicular phosphine ligands removed for clarity). The transition structure between two equivalent square pyramids (Ja) is a distorted trigonal bipyramid with an acute angle between H2 and H and the I ligand trans to it (5b). Such a structure, which is calculated to be very close in energy to the minimum and which has even been observed as a stable structure in the case of an Ru(I1) and two Ir(II1) complexes (with R and H at the acute angle),13v'4 should facilitate the exchange process by favoring the proximity between H and H2. a b a 5