8 research outputs found
Capture of Iodine Species in MIL-53(Al), MIL-120(Al), and HKUST-1(Cu) Periodic DFT and Ab-Initio Molecular Dynamics Studies
The
potential use of three metalāorganic frameworks (MIL-53Ā(Al),
MIL-120Ā(Al) and HKUST-1Ā(Cu)) to adsorb iodine species (I<sub>2</sub> and ICH<sub>3</sub>), which can be released during a severe nuclear
accident, is investigated using periodic dispersion density functional
theory for the first time. Competitive adsorption of iodine in the
presence of water molecules is also characterized for the hydrophilic
HKUST-1Ā(Cu). In the first step, we have found that the absolute values
of interaction energies of I<sub>2</sub> and ICH<sub>3</sub> are higher
in the hydrated form of HKUST-1Ā(Cu) than in the dehydrated one, which
is of very high interest for iodine trapping. In a second stage, iodine
species are strongly adsorbed in MIL-53Ā(Al) than in MIL-120Ā(Al) and
HKUST-1Ā(Cu) MOFs and therefore this material could potentially trap
iodine compounds. Moreover, we study the influence of the functionalization
of the MIL-53Ā(Al) organic linkers on the adsorption behavior of iodine
and it turns out that the substitutions does not present a significant
effect for this purpose. The factors governing the interaction energies
between iodine (I<sub>2</sub> and ICH<sub>3</sub>) and MOF structures
are analyzed and the important role of van der Waals interactions
in these materials is highlighted
TD-DFT Assessment of the Excited State Intramolecular Proton Transfer in Hydroxyphenylbenzimidazole (HBI) Dyes
Dyes
undergoing excited state intramolecular proton transfer (ESIPT)
received increasing attention during the last decades. If their unusual
large Stokes shifts and sometimes dual-fluorescence signatures have
paved the way toward new applications, the rapidity of ESIPT often
prevents its investigation with sole experimental approaches, and
theoretical simulations are often welcome, if necessary, to obtain
a full rationalization of the observations. In the present paper,
we evaluate both the absorption and the fluorescence spectra of, respectively,
the enol and keto forms of a series of hydroxyphenylbenzimidazole
(HBI) using a robust protocol based on Time-Dependent Density Functional
Theory (TD-DFT). Optical spectra were obtained accounting for both
vibronic and environmental effects. The aim of this work is therefore
not to evaluate the radiationless pathway going through the twisted
ESIPT structures, though excited-state reaction paths between enol
and keto forms have been rationalized. First we have compared three
dyes differing by the strength of the donor groups, and we have quantified
the impact of the flexible butyl chain substituting the imidazole
side. In accordance with experiments, we show that the presence of
a dialkylamino auxochrome allows to tune the excited-state potential
energy surface leading to a weaker tendency to ESIPT. This trend is
rationalized in terms of both structural and electronic effects. Next,
larger hydroxyphenyl-phenanthroimidazole (HPI) were considered to
assess the impact of a stronger Ļ-delocalization. 0ā0
energies and vibrationally resolved spectra of the corresponding fluoroborate
derivatives were studied as well. The dialkylamino auxochrome significantly
decreases the 0ā0 energies due to the presence of an important
charge transfer character, while the addition of a BODIPY moiety induces
a change of the emission signature now localized on the BODIPY side
rather than on the NBO core
Improving the Accuracy of Excited-State Simulations of BODIPY and Aza-BODIPY Dyes with a Joint SOS-CIS(D) and TD-DFT Approach
BODIPY and aza-BODIPY
dyes constitute two key families of organic
dyes with applications in both materials science and biology. Previous
attempts aiming to obtain accurate theoretical estimates of their
optical properties, and in particular of their 0ā0 energies,
have failed. Here, using time-dependent density functional theory
(TD-DFT), configuration interaction singles with a double correction
[CISĀ(D)], and its scaled-opposite-spin variant [SOS-CISĀ(D)], we have
determined the 0ā0 energies as well as the vibronic shapes
of both the absorption and emission bands of a large set of fluoroborates.
Indeed, we have selected 47 BODIPY and 4 aza-BODIPY dyes presenting
diverse chemical structures. TD-DFT yields a rather large mean signed
error between the experimental and theoretical 0ā0 energies
with a systematic overshooting of the transition energies (by ca.
0.4 eV). This error is reduced to ca. 0.2 [0.1] eV when the TD-DFT
0ā0 energies are corrected with vertical CISĀ(D) [SOS-CISĀ(D)]
energies. For BODIPY and aza-BODIPY dyes, both CISĀ(D) and SOS-CISĀ(D)
clearly outperform TD-DFT. The present computational protocol allows
accurate data to be obtained for the most relevant properties, that
is, 0ā0 energies and optical band shapes
Boranil and Related NBO Dyes: Insights From Theory
The
simulations of excited-state properties, that is, the 0ā0
energies and vibronic shapes, of a large panel of fluorophores presenting
a NBO atomic sequence have been achieved with a Time-Dependent Density
Functional Theory (TD-DFT) approach. We have combined eight hybrid
exchange-correlation functionals (B3LYP, PBE0, M06, BMK, M06-2X, CAM-B3LYP,
ĻB97X-D, and ĻB97) to the linear-response (LR) and the
state specific (SS) Polarizable Continuum Model (PCM) methods in both
their equilibrium (eq) and nonequilibrium (neq) limits. We show that
the combination of the SS-PCM scheme to a functional incorporating
a low amount of exact exchange can yield unphysical values for molecules
presenting large increase of their dipole moments upon excitation.
We therefore apply a functional possessing a large exact exchange
ratio to simulate the properties of NBO dyes, including large dyads
Excited-State Geometries of Solvated Molecules: Going Beyond the Linear-Response Polarizable Continuum Model
The
theoretical determination of excited-state structures remains
an active field of research, as these data are hardly accessible by
experimental approaches. In this contribution, we investigate excited-state
geometries obtained with Time-Dependent Density Functional Theory,
using both linear-response and, for the first time, corrected linear-response
approaches of the Polarizable Continuum Model. Several chromophores
representative of key dye families are used. In most cases, the corrected
linear-response approach provides bond distances in between the gas
and linear-response data, the latter model providing larger medium-induced
structural changes than the corrected linear-response model. However,
in a few cases, the solvation effects predicted by the two continuum
approaches present opposite directions compared to the gas phase reference
Optical Signatures of OBO Fluorophores: A Theoretical Analysis
Dioxaborines dyes,
based on the OBO atomic sequence, constitute
one promising series of molecules for both organic electronics and
bioimaging applications. Using Time-Dependent Density Functional Theory,
we have simulated the optical signatures of these fluoroborates. In
particular, we have computed the 0ā0 energies and shapes of
both the absorption and the emission bands. To assess the importance
of solvent effects three polarization schemes have been applied within
the Polarizable Continuum Model: the linear-response (LR), the corrected
linear-response (cLR), and the state-specific (SS). We show that the
SS approach is unable to yield consistent chemical trends for these
challenging compounds that combine charge-transfer and cyanine characters.
On the contrary, LR and cLR are more effective in reproducing chemical
trends in OBO dyes. We have applied our computational protocol not
only to analyze the signatures of existing dyes but also to design
structures with red-shifted absorption and emission bands
Combining the BetheāSalpeter Formalism with Time-Dependent DFT Excited-State Forces to Describe Optical Signatures: NBO Fluoroborates as Working Examples
We
propose to use a blend of methodologies to tackle a challenging
case for quantum approaches: the simulation of the optical properties
of asymmetric fluoroborate derivatives. Indeed, these dyes, which
present a low-lying excited-state exhibiting a cyanine-like nature,
are treated not only with the Time-Dependent Density Functional Theory
(TD-DFT) method to determine both the structures and vibrational patterns
but also with the BetheāSalpeter approach to compute both the
vertical absorption and emission energies. This combination allows
us to obtain 0ā0 energies with a significantly improved accuracy
compared to the ārawā TD-DFT estimates. We also discuss
the impact of various declinations of the Polarizable Continuum Model
(linear-response, corrected linear-response, and state-specific models)
on the obtained accuracy
On the Computation of Adiabatic Energies in Aza-Boron-Dipyrromethene Dyes
We have simulated the optical properties of Aza-Boron-dipyrromethene
(Aza-BODIPY) dyes and, more precisely, the 0ā0 energies as
well as the shape of both absorption and fluorescence bands, thanks
to the computation of vibronic couplings. To this end, time-dependent
density functional theory (TD-DFT) calculations have been carried
out with a systematic account of both vibrational and solvent effects.
In a first step, we assessed different atomic basis sets, a panel
of global and range-separated hybrid functionals as well as different
solvent models (linear-response, corrected linear-response, and state-specific).
In this way, we have defined an accurate yet efficient protocol for
these dyes. In a second stage, several simulations have been carried
out to investigate acidochromic and complexation effects, as well
as the impact of side groups on the topology of the optical bands.
In each case, theory is able to accurately reproduce experimental
results and the proposed protocol is consequently useful to design
new dyes featuring improved properties