9 research outputs found
Accurate Treatment of Large Supramolecular Complexes by Double-Hybrid Density Functionals Coupled with Nonlocal van der Waals Corrections
In this work, we present a thorough
assessment of the performance
of some representative double-hybrid density functionals (revPBE0-DH-NL
and B2PLYP-NL) as well as their parent hybrid and GGA counterparts,
in combination with the most modern version of the nonlocal (NL) van
der Waals correction to describe very large weakly interacting molecular
systems dominated by noncovalent interactions. Prior to the assessment,
an accurate and homogeneous set of reference interaction energies
was computed for the supramolecular complexes constituting the L7
and S12L data sets by using the novel, precise, and efficient DLPNO-CCSD(T)
method at the complete basis set limit (CBS). The correction of the
basis set superposition error and the inclusion of the deformation
energies (for the S12L set) have been crucial for obtaining precise
DLPNO-CCSD(T)/CBS interaction energies. Among the density functionals
evaluated, the double-hybrid revPBE0-DH-NL and B2PLYP-NL with the
three-body dispersion correction provide remarkably accurate association
energies very close to the chemical accuracy. Overall, the NL van
der Waals approach combined with proper density functionals can be
seen as an accurate and affordable computational tool for the modeling
of large weakly bonded supramolecular systems
Bending Carbon Nanoforms for Supramolecular Recognition: A Topological Study on Hemifullerene-Based Aggregates
Buckybowls
have risen as appealing fullerene fragment derivatives.
Their intrinsic curvature has been exploited in the generation of
host–guest supramolecular assemblies, not only through concave–convex
complementarity but also through less-known concave–concave
staggered arrangements. Whereas the stabilization of bowl-in-bowl
dispositions has been ascribed to efficient π–π
forces together with favorable dipole–dipole interactions,
a detailed analysis on the forces guiding the formation of the staggered
arrangements is missing so far. Herein, we present a thorough theoretical
characterization of bowl-in-bowl vs staggered hemifullerene-based
homodimers and heterodimers with the electron-donor truxTTF molecule,
as test cases, under the density functional theory and by means of
chemical bonding techniques. Our results clearly reveal strong and
localized noncovalent signatures, together with an enhanced orbital
interaction, associated with CH−π and sulfur-mediated
interactions governing the staggered formation. Bending the fullerene
fragment is demonstrated to favor the stabilization in both homo-
and heterodimers, in good accord with the depletion in the π-electron
density calculated upon increasing the buckybowl curvature. The optimal
buckybowl curvature for the highest interaction energy is, however,
dependent on the type of supramolecular assembly (bowl-in-bowl vs
staggered) and the concave region to which hemifullerene approaches
truxTTF. Interestingly, two regimes are found as a function of buckybowl
curvature for hemifullerene homodimers: bowl-in-bowl dispositions
are calculated more stable at low curvatures whereas staggered dimers
prevail for highly curved buckybowls. Our results highlight the potential
of discrete CH−π and sulfur-mediated interactions to
generate unconventional staggered supramolecular arrangements toward
the development of a new and unexplored host–guest chemistry
Efficient Light Harvesters Based on the 10-(1,3-Dithiol-2-ylidene)anthracene Core
Three new push–pull chromophores based on the 10-(1,3-dithiol-2-ylidene)anthracene core were synthesized and fully characterized. The new chromophores display broad absorption spectra, nearly covering the whole visible region, with high extinction coefficients. Electrochemistry and theoretical calculations allowed the understanding of these singular electronic properties. The molecular structures were unambiguously confirmed by X-ray diffraction
Efficient Light Harvesters Based on the 10-(1,3-Dithiol-2-ylidene)anthracene Core
Three new push–pull chromophores based on the 10-(1,3-dithiol-2-ylidene)anthracene core were synthesized and fully characterized. The new chromophores display broad absorption spectra, nearly covering the whole visible region, with high extinction coefficients. Electrochemistry and theoretical calculations allowed the understanding of these singular electronic properties. The molecular structures were unambiguously confirmed by X-ray diffraction
Efficient Light Harvesters Based on the 10-(1,3-Dithiol-2-ylidene)anthracene Core
Three new push–pull chromophores based on the 10-(1,3-dithiol-2-ylidene)anthracene core were synthesized and fully characterized. The new chromophores display broad absorption spectra, nearly covering the whole visible region, with high extinction coefficients. Electrochemistry and theoretical calculations allowed the understanding of these singular electronic properties. The molecular structures were unambiguously confirmed by X-ray diffraction
Efficient Light Harvesters Based on the 10-(1,3-Dithiol-2-ylidene)anthracene Core
Three new push–pull chromophores based on the 10-(1,3-dithiol-2-ylidene)anthracene core were synthesized and fully characterized. The new chromophores display broad absorption spectra, nearly covering the whole visible region, with high extinction coefficients. Electrochemistry and theoretical calculations allowed the understanding of these singular electronic properties. The molecular structures were unambiguously confirmed by X-ray diffraction
Tuning the Electronic Properties of Nonplanar exTTF-Based Push–Pull Chromophores by Aryl Substitution
A new family of π-extended tetrathiafulvalene (exTTF)
donor–acceptor
chromophores has been synthesized by [2 + 2] cycloaddition of TCNE
with exTTF-substituted alkynes and subsequent cycloreversion. X-ray
data and theoretical calculations, performed at the B3LYP/6-31G**
level, show that the new chromophores exhibit highly distorted nonplanar
molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene
(TCBD) units. The electronic and optical properties, investigated
by UV/vis spectroscopy and electrochemical measurements, are significantly
modified when the TCBD acceptor unit is substituted with a donor phenyl
group, which increases the twisting of the TCBD units and reduces
the conjugation between the two dicyanovinyl subunits. The introduction
of phenyl substituents hampers the oxidation and reduction processes
and, at the same time, largely increases the optical band gap. An
effective electronic communication between the donor and acceptor
units, although limited by the distorted molecular geometry, is evidenced
both in the ground and in the excited electronic states. The electronic
absorption spectra are characterized by low- to medium-intense charge-transfer
bands that extend to the near-infrared
Conjugated Porphyrin Dimers: Cooperative Effects and Electronic Communication in Supramolecular Ensembles with C<sub>60</sub>
Two new conjugated porphyrin-based
systems (dimers <b>3</b> and <b>4</b>) endowed with suitable
crown ethers have been
synthesized as receptors for a fullerene-ammonium salt derivative
(<b>1</b>). Association constants in solution have been determined
by UV–vis titration experiments in CH<sub>2</sub>Cl<sub>2</sub> at room temperature. The designed hosts are able to associate up
to two fullerene-based guest molecules and present association constants
as high as ∼5 × 10<sup>8</sup> M<sup>–1</sup>.
Calculation of the allosteric cooperative factor α for supramolecular
complexes <b>[3·1</b><sub><b>2</b></sub><b>]</b> and <b>[4·1</b><sub><b>2</b></sub><b>]</b> showed a negative cooperative effect in both cases. The interactions
accounting for the formation of the associates are based, first, on
the complementary ammonium-crown ether interaction and, second, on
the π–π interactions between the porphyrin rings
and the C<sub>60</sub> moieties. Theoretical calculations have evidenced
a significant decrease of the electron density in the porphyrin dimers <b>3</b> and <b>4</b> upon complexation of the first C<sub>60</sub> molecule, in good agreement with the negative cooperativity
found in these systems. This negative effect is partially compensated
by the stabilizing C<sub>60</sub>–C<sub>60</sub> interactions
that take place in the more stable <i>syn</i>-disposition
of <b>[4·1</b><sub><b>2</b></sub><b>]</b>
Tuning the Electronic Properties of Nonplanar exTTF-Based Push–Pull Chromophores by Aryl Substitution
A new family of π-extended tetrathiafulvalene (exTTF)
donor–acceptor
chromophores has been synthesized by [2 + 2] cycloaddition of TCNE
with exTTF-substituted alkynes and subsequent cycloreversion. X-ray
data and theoretical calculations, performed at the B3LYP/6-31G**
level, show that the new chromophores exhibit highly distorted nonplanar
molecular structures with largely twisted 1,1,4,4-tetracyanobuta-1,3-diene
(TCBD) units. The electronic and optical properties, investigated
by UV/vis spectroscopy and electrochemical measurements, are significantly
modified when the TCBD acceptor unit is substituted with a donor phenyl
group, which increases the twisting of the TCBD units and reduces
the conjugation between the two dicyanovinyl subunits. The introduction
of phenyl substituents hampers the oxidation and reduction processes
and, at the same time, largely increases the optical band gap. An
effective electronic communication between the donor and acceptor
units, although limited by the distorted molecular geometry, is evidenced
both in the ground and in the excited electronic states. The electronic
absorption spectra are characterized by low- to medium-intense charge-transfer
bands that extend to the near-infrared