Hydrogen-bonded hexameric cluster of benzyl alcohol in the solid state polymeric organization of <i>p</i>-<i>tert</i>-Butylcalix[5]arene

<p>An uncommon hydrogen-bonded hexameric cluster of benzyl alcohol (<b>2</b>) was formed in hydrophobic space in the layered organisation of the one-dimensional polymeric zigzag array of <b>1</b> in the solid state. The hexameric cluster adopted a distorted cyclohexane-like (12) O–H⋯O hydrogen bond network. The formation of the hexameric cluster was quite sensitive to a tiny structural difference of guests; phenylethylalcohol (<b>3</b>), phenol (<b>4</b>), benzyl amine (<b>5</b>) and aniline (<b>6</b>) did not form any hexameric cluster. The packing coefficient of 0.53 suggested that the hexameric cluster nicely filled the hydrophobic space, which most likely resulted in the effective van der Waals contacts that stabilised the supramolecular organisation composed of the hexameric cluster and the polymeric array of <b>1</b> in the solid state.</p

Modified Synthesis and Supramolecular Polymerization of Rim-to-Rim Connected Bisresorcinarenes

The acid-catalyzed condensation reaction of resorcinol and bisdimethoxyacetals gave rise to rim-to-rim connected bisresorcinarenes in good yields. In the presence of ethanol, the homoditopic bisresorcinarenes assembled to form supramolecular polymers via hydrogen bonding interactions. The fibrous morphologies of the supramolecular polymers were confirmed by atomic force microscopy and scanning electron microscopy

Modified Synthesis and Supramolecular Polymerization of Rim-to-Rim Connected Bisresorcinarenes

The acid-catalyzed condensation reaction of resorcinol and bisdimethoxyacetals gave rise to rim-to-rim connected bisresorcinarenes in good yields. In the presence of ethanol, the homoditopic bisresorcinarenes assembled to form supramolecular polymers via hydrogen bonding interactions. The fibrous morphologies of the supramolecular polymers were confirmed by atomic force microscopy and scanning electron microscopy

Synthesis and Structure of Feet-to-Feet Connected Bisresorcinarenes

Bisresorcinarenes <b>1a</b>–<b>d</b> were obtained in excellent yields, and <b>1e</b> was finally obtained in 50% yield. X-ray diffraction analysis showed that <b>1a</b> and <b>1b</b> adopted helical conformations, whereas the two resorcinarenes of <b>1c</b>–<b>e</b> were in parallel orientations in which the clefts of the aliphatic chains entrapped one or two solvent molecules. The conformational study revealed that the helix interconversion between the (<i>P</i>)- and (<i>M</i>)-helical conformers depended on the length of the aliphatic chains. <b>1a</b> had the largest energetic barrier to helix interconversion, while in <b>1b</b>, its more flexible aliphatic chains lowered its energetic barriers. The <i>P</i>/<i>M</i> interconversion of <b>1a</b> was coupled with the clockwise/anticlockwise interconversion of the interannular hydrogen bonding of the two resorcinarenes. The large negative entropic contributions indicate that the transition state is most likely more ordered than the ground states, suggesting that the transition state is most likely symmetric and is solvated by water molecules. Calculations at the M06-2<i>X</i>/6-31G­(d,p) level revealed that the more stable (<i>P</i>)-conformation has clockwise interannular hydrogen bonding between the two resorcinarenes

Anomalous Cage Effect of the Excited State Dynamics of Catechol in the 18-Crown-6–Catechol Host–Guest Complex

We determined the number of isomers and their structures for the 18-crown-6 (18C6)–catechol host–guest complex, and examined the effect of the complex formation on the S₁ (¹ππ*) dynamics of catechol under a supersonically cooled gas phase condition and in cyclohexane solution at room temperature. In the gas phase experiment, UV–UV hole-burning spectra of the 18C6–catechol 1:1 complex indicate that there are three stable isomers. For bare catechol, it has been reported that two adjacent OH groups have an intramolecular hydrogen (H) bond. The IR–UV double resonance spectra show two types of isomers in the 18C6–catechol 1:1 complex; one of the three 18C6–catechol 1:1 isomers has the intramolecular H-bond between the two OH groups, while in the other two isomers the intramolecular H-bond is broken and the two OH groups are H-bonded to oxygen atoms of 18C6. The complex formation with 18C6 substantially elongates the S₁ lifetime from 7 ps for bare catechol and 2.0 ns for the catechol–H₂O complex to 10.3 ns for the 18C6–catechol 1:1 complex. Density functional theory calculations of the 18C6–catechol 1:1 complex suggest that this elongation is attributed to a larger energy gap between the S₁ (¹ππ*) and ¹πσ* states than that of bare catechol or the catechol–H₂O complex. In cyclohexane solution, the enhancement of the fluorescence intensity of catechol was found by adding 18C6, due to the formation of the 18C6–catechol complex in solution, and the complex has a longer S₁ lifetime than that of catechol monomer. From the concentration dependence of the fluorescence intensity, we estimated the equilibrium constant <i>K</i> for the 18C6 + catechol ⇄ 18C6–catechol reaction. The obtained value (log <i>K</i> = 2.3) in cyclohexane is comparable to those for alkali metal ions or other molecular ions, indicating that 18C6 efficiently captures catechol in solution. Therefore, 18C6 can be used as a sensitive sensor of catechol derivatives in solution with its high ability of fluorescence enhancement

Synthesis of Optically Active Poly(<i>m</i>‑phenyleneethynylene–aryleneethynylene)s Bearing Hydroxy Groups and Examination of the Higher Order Structures

Novel optically active poly­(<i>m</i>-phenyleneethynylene–aryleneethynylene)­s bearing hydroxy groups with various arylene units {poly­[(<i>S</i>)-/(<i>R</i>)-<b>1</b>–<b>3a</b>]–poly­[(<i>R</i>)-<b>1</b>–<b>3e</b>] and poly­[(<i>S</i>)-<b>2</b>–<b>3a</b>]} were synthesized by the Sonogashira–Hagihara coupling polymerization of 3,5-diiodo-4-hydroxy-C₆H₄CONHCH­(CH₃)­COXC₁₂H₂₅ [(<i>S</i>)-/(<i>R</i>)-<b>1</b> (X = O), (<i>S</i>)-<b>2</b> (X = NH)] with HCC–Ar–CCH [<b>3a</b> (Ar = 1,4-C₆H₄), <b>3b</b> (Ar = 1,4-C₆H₄-1,4-C₆H₄−), <b>3c</b> (Ar = 1,4-C₆H₄-1,4-C₆H₄-1,4-C₆H₄−), <b>3d</b> (Ar = 2,5-dihexyl-1,4-C₆H₂), <b>3e</b> (Ar = 2,5-didodecyl-1,4-C₆H₂)]. The yields and number-average molecular weights of the polymers were in the ranges 60–94% and 7,000–29,500 with no correlation between the yield and the <i>M</i>_n. Circular dichroism (CD), UV–vis, and fluorescence spectroscopic analyses indicated that poly­[(<i>S</i>)-<b>1</b>–<b>3a</b>]–poly­[(<i>S</i>)-<b>1</b>–<b>3c</b>] and poly­[(<i>S</i>)-<b>2</b>–<b>3a</b>] formed predominantly one-handed helical structures in THF, while poly­[(<i>S</i>)-<b>1</b>–<b>3d</b>] and poly­[(<i>S</i>)-<b>1</b>–<b>3e</b>] showed no evidence for forming chirally ordered structures. All polymers emitted blue fluorescence. The solution state IR measurement revealed the presence of intramolecular hydrogen bonding between the amide groups at the side chains of poly­[(<i>S</i>)-<b>1</b>–<b>2a</b>]. The helical structures and helix-forming abilities of the polymers were analyzed by the molecular mechanics (MM), semiempirical molecular orbital (MO) and density functional theory (DFT) methods. Tube-like structures, presumably formed by perpendicular aggregation of the helical polymers, were observed by atomic force microscopy (AFM)

Induced-Dipole-Directed, Cooperative Self-Assembly of a Benzotrithiophene

A benzotrithiophene derivative possessing phenylisoxazoles self-assembled to form stacks. The molecule isodesmically self-assembled in chloroform, whereas it self-assembled in a cooperative fashion in decalin and in methylcyclohexane. Thermodynamic studies based on isodesmic, van der Schoot, and Goldstein–Stryer mathematical models revealed that the self-assembly processes are enthalpically driven and entropically opposed. An enthalpy–entropy compensation plot indicates that the assembly processes in chloroform, decalin, and methylcyclohexane are closely related. The enthalpic gains in less-polar solvents are greater than those in more-polar solvents, resulting in the formation of large assemblies in decalin and in methylcyclohexane. The formation of large assemblies leads to cooperative assemblies. The elongation process is enthalpically more favored than the nucleation process, which drives the cooperativity of the self-assembly. DFT calculations suggested that a hexameric assembly is more stable than tetrameric or dimeric assemblies. Cooperative self-assemblies based on intermolecular interactions other than hydrogen bonding have rarely been reported. It is demonstrated herein that van der Waals interactions, including induced dipole–dipole interactions, can drive the cooperative assembly of planar π-conjugated molecules

Cooperative Self-Assembly of Carbazole Derivatives Driven by Multiple Dipole–Dipole Interactions

Carbazole possessing phenylisoxazoles self-assembled in a cooperative manner in decalin. X-ray crystal structure analysis revealed that the isoxazole dipoles align in a head-to-tail fashion. DFT calculations suggested that the linear array of dipoles induced the polarization of each dipole, leading to an increase in dipole–dipole interactions. This dipole polarization resulted in cooperative assembly

Conversion from Pillar[5]arene to Pillar[6–15]arenes by Ring Expansion and Encapsulation of C₆₀ by Pillar[<i>n</i>]arenes with Nanosize Cavities

Conversion of ring size from pillar[5]­arene to pillar[6–15]­arenes and isolation of pillar­[<i>n</i>]­arene homologues (<i>n</i> = 11–13) with known pillar­[<i>n</i>]­arene homologues (<i>n</i> = 6–10) are demonstrated. Pillar[10]­arene formed the most stable host–guest complex with C₆₀ among the pillar[5–14]­arenes

Spectrally Selective Leakage of Light from Self-Assembled Supramolecular Nanofiber Waveguides Induced by Surface Plasmon Polaritons

We report surface plasmon polariton (SPP)-induced spectrally selective leakage of light waveguided in supramolecular nanofibers. The nanofibers are fabricated by self-assembly of tris(phenylisoxazolyl)benzene derivative molecules, and their diameter ranges from nanometers to hundreds of nanometers. Nanofibers with heights of more than 200 nm are shown to function as waveguides for fluorescence excited in one location by a focused 360 nm laser. The fluorescence can transfer the whole length of the nanofibers of tens of micrometers and is outcoupled from the nanofiber ends. The waveguiding phenomenon dramatically changes when the nanofibers are deposited on SPP-generating substrates. The substrates in the form of nanohole arrays are fabricated on a gold film with a pitch of 500 nm, a diameter of 250 nm, and a depth of 40 nm. On the SPP substrates, the nanofiber waveguides exhibit strong leakage of the guided light. The spectrum of the leaked light is consistent with the SPP resonance wavelength, and its polarization corresponds to the TE waveguided mode. We propose mechanisms of the observed phenomena that include either excitation of the SPPs via the waveguide evanescent field or direct enhancement of the leakage by the modified density of states near the plasmonic substrate