12 research outputs found
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>/6-31GÂ(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 S<sub>1</sub> (<sup>1</sup>ππ*) 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 S<sub>1</sub> lifetime from
7 ps for bare catechol and 2.0 ns for the catechol–H<sub>2</sub>O 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 S<sub>1</sub> (<sup>1</sup>ππ*) and <sup>1</sup>πσ* states than that of bare catechol or the catechol–H<sub>2</sub>O 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 S<sub>1</sub> 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 polyÂ(<i>m</i>-phenyleneethynylene–aryleneethynylene)Âs
bearing hydroxy groups with various arylene units {polyÂ[(<i>S</i>)-/(<i>R</i>)-<b>1</b>–<b>3a</b>]–polyÂ[(<i>R</i>)-<b>1</b>–<b>3e</b>] and polyÂ[(<i>S</i>)-<b>2</b>–<b>3a</b>]} were synthesized
by the Sonogashira–Hagihara coupling polymerization of 3,5-diiodo-4-hydroxy-C<sub>6</sub>H<sub>4</sub>CONHCHÂ(CH<sub>3</sub>)ÂCOXC<sub>12</sub>H<sub>25</sub> [(<i>S</i>)-/(<i>R</i>)-<b>1</b> (X = O), (<i>S</i>)-<b>2</b> (X = NH)] with HCî—¼C–Ar–Cî—¼CH
[<b>3a</b> (Ar = 1,4-C<sub>6</sub>H<sub>4</sub>), <b>3b</b> (Ar = 1,4-C<sub>6</sub>H<sub>4</sub>-1,4-C<sub>6</sub>H<sub>4</sub>−), <b>3c</b> (Ar = 1,4-C<sub>6</sub>H<sub>4</sub>-1,4-C<sub>6</sub>H<sub>4</sub>-1,4-C<sub>6</sub>H<sub>4</sub>−), <b>3d</b> (Ar = 2,5-dihexyl-1,4-C<sub>6</sub>H<sub>2</sub>), <b>3e</b> (Ar = 2,5-didodecyl-1,4-C<sub>6</sub>H<sub>2</sub>)]. 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><sub>n</sub>. Circular
dichroism (CD), UV–vis, and fluorescence spectroscopic analyses
indicated that polyÂ[(<i>S</i>)-<b>1</b>–<b>3a</b>]–polyÂ[(<i>S</i>)-<b>1</b>–<b>3c</b>] and polyÂ[(<i>S</i>)-<b>2</b>–<b>3a</b>] formed predominantly one-handed helical structures in
THF, while polyÂ[(<i>S</i>)-<b>1</b>–<b>3d</b>] and polyÂ[(<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 polyÂ[(<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 C<sub>60</sub> by Pillar[<i>n</i>]arenes with Nanosize Cavities
Conversion
of ring size
from pillar[5]Âarene to pillar[6–15]Âarenes and isolation of
pillarÂ[<i>n</i>]Âarene homologues (<i>n</i> = 11–13)
with known pillarÂ[<i>n</i>]Âarene homologues (<i>n</i> = 6–10) are demonstrated. Pillar[10]Âarene formed the most
stable host–guest complex with C<sub>60</sub> among the pillar[5–14]Âarenes
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