24 research outputs found
Solid-State Dilution of Dihydroxybenzophenones with 4,13-Diaza-18-crown-6 for Photocrystallographic Studies
This work forms part of the ongoing drive toward identifying
and
developing suitable light sensitive substances for photocrystallographic
studies. In order to investigate the solid-state dilution of the photoactive
dihydroxybenzophenone, X-ray crystal structures of three dihydroxybenzophenone·4,13-diaza-18-crown-6
co-crystals are reported and analyzed. The dihydroxybenzophenone molecules
within the co-crystal are compared to those observed in homomolecular
dihydroxybenzophenone crystals in terms of their intermolecular contacts,
bond geometry and conformation. Molecular volumes and void spaces
were calculated using Voronoi–Dirichlet polyhedra and Hirshfeld
surface-based space partitioning, demonstrating new ways to represent
potential reaction cavities around a photoactive molecule and calculate
their packing efficiency. In each case the conditions of solid-state
dilution were met. The molecular conformations of the homomolecular
environments are retained to varying degrees in the analogous co-crystals.
Results show that the co-crystals studied are potentially suitable
for photocrystallography. In particular, 2,4-dihydroxybenzophenone
molecules in 4,13-diaza-18-crown-6·2(2,4-dihydroxybenzophenone)
co-crystals exhibit high structural similarity to their homomolecular
analogues suggesting its photochemical properties could be common
to both environments
Photoconversion Bonding Mechanism in Ruthenium Sulfur Dioxide Linkage Photoisomers Revealed by in Situ Diffraction
Three new ruthenium–sulfur dioxide linkage photoisomeric
complexes in the [Ru(NH<sub>3</sub>)<sub>4</sub>(SO<sub>2</sub>)<b>X</b>]Cl<sub>2</sub>·H<sub>2</sub>O family (<b>X</b> = pyridine (<b>1</b>); 3-chloropyridine (<b>2</b>);
4-chloropyridine (<b>3</b>)) have been developed in order to
examine the effects of the <i>trans</i>-ligand on the nature
of the photo-induced SO<sub>2</sub> coordination to the ruthenium
ion. Solid-state metastable η<sup>1</sup>-O-bound (MS1) and
η<sup>2</sup>-side S,O-bound (MS2) photoisomers are crystallographically
resolved by probing a light-induced crystal with in situ diffraction.
This so-called photocrystallography reveals the highest known photoconversion
fraction of 58(3)% (in <b>1</b>) for any solid-state SO<sub>2</sub> linkage photoisomer. The decay of this MS1 into the MS2 state
was modeled via first-order kinetics with a non-zero asymptote. Furthermore,
the MS2 decay kinetics of the three compounds were examined according
to their systematically varying <i>trans</i>-ligand <b>X</b>; this offers the first experimental evidence that the MS2
state is primarily stabilized by donation from the S–O<sub>bound</sub> electrons into the Ru dσ-orbital rather than π-backbonding
as previously envisaged. This has important consequences for the optoelectronic
application of these materials since this establishes, for the first
time, a design protocol that will enable one to control their photoconversion
levels
Photoconversion Bonding Mechanism in Ruthenium Sulfur Dioxide Linkage Photoisomers Revealed by in Situ Diffraction
Three new ruthenium–sulfur dioxide linkage photoisomeric
complexes in the [Ru(NH<sub>3</sub>)<sub>4</sub>(SO<sub>2</sub>)<b>X</b>]Cl<sub>2</sub>·H<sub>2</sub>O family (<b>X</b> = pyridine (<b>1</b>); 3-chloropyridine (<b>2</b>);
4-chloropyridine (<b>3</b>)) have been developed in order to
examine the effects of the <i>trans</i>-ligand on the nature
of the photo-induced SO<sub>2</sub> coordination to the ruthenium
ion. Solid-state metastable η<sup>1</sup>-O-bound (MS1) and
η<sup>2</sup>-side S,O-bound (MS2) photoisomers are crystallographically
resolved by probing a light-induced crystal with in situ diffraction.
This so-called photocrystallography reveals the highest known photoconversion
fraction of 58(3)% (in <b>1</b>) for any solid-state SO<sub>2</sub> linkage photoisomer. The decay of this MS1 into the MS2 state
was modeled via first-order kinetics with a non-zero asymptote. Furthermore,
the MS2 decay kinetics of the three compounds were examined according
to their systematically varying <i>trans</i>-ligand <b>X</b>; this offers the first experimental evidence that the MS2
state is primarily stabilized by donation from the S–O<sub>bound</sub> electrons into the Ru dσ-orbital rather than π-backbonding
as previously envisaged. This has important consequences for the optoelectronic
application of these materials since this establishes, for the first
time, a design protocol that will enable one to control their photoconversion
levels
Remote Substituent Effects on the Structures and Stabilities of PE π‑Stabilized Diphosphatetrylenes (R<sub>2</sub>P)<sub>2</sub>E (E = Ge, Sn)
A rare P–E
π interaction between the lone pair of a planar P center and
the vacant p orbital at the Ge or Sn center provides efficient stabilization
for P-substituted tetrylenes (R<sub>2</sub>P)<sub>2</sub>E (E = Ge,
Sn) and enables isolation of the first example of a compound with
a crystallographically authenticated PSn bond. Subtle changes
in the electronic properties of the bulky aryl substituents in these
compounds change the preference for planar versus pyramidal P centers
in the solid state; however, variable-temperature NMR spectroscopy
indicates that in solution these species are subject to a dynamic
equilibrium, which interconverts the planar and pyramidal P centers.
Consistent with this, density functional theory studies suggest that
there is only a small energy difference between the planar and pyramidal
forms of these compounds and reveal a small singlet–triplet
energy separation, suggesting potentially interesting reactivities
Molecular Origins of Optoelectronic Properties in Coumarins 343, 314T, 445, and 522B
The relationships between the structure
and laser dye properties
of four coumarin derivatives are investigated to assist in knowledge-based
molecular design of coumarins for various optoelectronic applications.
Four new crystal structures of coumarins 343, 314T, 445, and 522B
are determined at 120 K and analyzed via the empirical harmonic–oscillator–stabilization–energy
and bond-length–alternation models, based on resonance theory.
Results from these analyses are used to rationalize the optoelectronic
properties of these coumarins, such as their UV–vis peak absorption
wavelength, molar extinction coefficient, and fluorescence quantum
efficiency. The specific molecular structural features of these four
coumarins and the effects on their optoelectronic properties are further
examined via a comparison with other similar coumarin derivatives,
including coumarins 314, 500, and 522. These findings are corroborated
by density functional theory (DFT) and time-dependent DFT calculations.
The structure–property correlations revealed herein provide
a foundation for the molecular engineering of coumarins with “dial-up”
optoelectronic properties to suit a given device application
Molecular and Supramolecular Origins of Optical Nonlinearity in <i>N</i>‑Methylurea
The delicate balance between solid-state
intermolecular interactions
and electron-donating methyl-group influences in <i>N</i>-methylurea (NMU) is shown to distinguish its nonlinear optical properties,
relative to those of urea, a standard reference material for second
harmonic generation (SHG). The solid-state intermolecular interactions
in NMU are identified using neutron diffraction data, showing that
hydrogen bonding generates an extensive 3D supramolecular network
of NMU molecules with secondary and tertiary nonbonded contacts helping
to hold this network in a closely packed form. The undulating “urea
tape” motif within this network renders an overall packing
arrangement that is less SHG-favorable than that of urea, which exhibits
a more head-to-tail molecular alignment. The primary, secondary, and
tertiary nonbonded contacts are classified using graph-sets, Hirshfeld
surfaces, and fingerprint plots. H···H contacts in
NMU contribute to the overall Hirshfeld surface area much more than
in urea, forming at the expense of O···H interactions.
However, SHG-contributing electronic effects of the methyl group in
NMU provide some compensation to these hydrogen-bonding influences.
This methyl group is also shown to librate, which could augment SHG.
Our experimental results offer a direct response to previous density
functional theory calculations on NMU and urea, corroborating their predictions as well as enabling a better
relationship between the molecular and bulk optical nonlinearity of
NMU. To that end, crystal engineering options are discussed with a
view to balancing these seemingly conflicting structural attributes,
so that one can produce an SHG-active form of NMU that is superior
to urea
Relating Electron Donor and Carboxylic Acid Anchoring Substitution Effects in Azo Dyes to Dye-Sensitized Solar Cell Performance
The
relationship between the molecular structures of a series of
azo dyes and their operational performance when applied to dye-sensitized
solar cells (DSSCs) is probed via experimental and computational analysis.
Seven azo dyes, with three different donating groups (dimethylamino,
diethylamino, and dipropylamino)
and carboxylic acid anchoring positions (<i>ortho</i>-, <i>meta</i>-, and <i>para</i>-substituted phenyl rings)
are studied. Single-crystal X-ray diffraction is employed in order
to analyze the effects of conformation and quantify the contribution
of quinoidal resonance forms to the intramolecular charge transfer
(ICT), which controls their intrinsic photovoltaic potential from
an electronic standpoint. Harmonic oscillator stabilization energy
(HOSE) calculations indicate that the <i>para</i>- and <i>ortho</i>-azo dyes exhibit potential for DSSC application. However,
from a geometrical standpoint, the crystal structure data, proton
nuclear magnetic resonance spectroscopy (<sup>1</sup>H NMR), and density
functional theory (DFT) all indicate that intramolecular hydrogen
bonds form in <i>ortho</i>-dyes within both solid and solution
states, impeding their intrinsic ICT-based photovoltaic potential,
and offering insights into the photostability of azo dyes and the
dye···TiO<sub>2</sub> anchoring mechanism in DSSCs.
Donor effects are manifested in the packing mode and molecular planarity
revealed by X-ray crystallography and in the UV/vis absorption spectra.
DFT and time-dependent density functional theory (TDDFT) were performed
to understand the electronic and optical properties of these azo dyes;
these calculations compare well with experimental findings. Operational
tests of DSSCs, functionalized by these azo dyes, show that the carboxylic
acid anchoring position plays a crucial role in DSSC performance,
while donating groups offer a much less obvious effect on the overall
DSSC device efficiency
Relating Electron Donor and Carboxylic Acid Anchoring Substitution Effects in Azo Dyes to Dye-Sensitized Solar Cell Performance
The
relationship between the molecular structures of a series of
azo dyes and their operational performance when applied to dye-sensitized
solar cells (DSSCs) is probed via experimental and computational analysis.
Seven azo dyes, with three different donating groups (dimethylamino,
diethylamino, and dipropylamino)
and carboxylic acid anchoring positions (<i>ortho</i>-, <i>meta</i>-, and <i>para</i>-substituted phenyl rings)
are studied. Single-crystal X-ray diffraction is employed in order
to analyze the effects of conformation and quantify the contribution
of quinoidal resonance forms to the intramolecular charge transfer
(ICT), which controls their intrinsic photovoltaic potential from
an electronic standpoint. Harmonic oscillator stabilization energy
(HOSE) calculations indicate that the <i>para</i>- and <i>ortho</i>-azo dyes exhibit potential for DSSC application. However,
from a geometrical standpoint, the crystal structure data, proton
nuclear magnetic resonance spectroscopy (<sup>1</sup>H NMR), and density
functional theory (DFT) all indicate that intramolecular hydrogen
bonds form in <i>ortho</i>-dyes within both solid and solution
states, impeding their intrinsic ICT-based photovoltaic potential,
and offering insights into the photostability of azo dyes and the
dye···TiO<sub>2</sub> anchoring mechanism in DSSCs.
Donor effects are manifested in the packing mode and molecular planarity
revealed by X-ray crystallography and in the UV/vis absorption spectra.
DFT and time-dependent density functional theory (TDDFT) were performed
to understand the electronic and optical properties of these azo dyes;
these calculations compare well with experimental findings. Operational
tests of DSSCs, functionalized by these azo dyes, show that the carboxylic
acid anchoring position plays a crucial role in DSSC performance,
while donating groups offer a much less obvious effect on the overall
DSSC device efficiency
Molecular Origins of Optoelectronic Properties in Coumarins 343, 314T, 445, and 522B
The relationships between the structure
and laser dye properties
of four coumarin derivatives are investigated to assist in knowledge-based
molecular design of coumarins for various optoelectronic applications.
Four new crystal structures of coumarins 343, 314T, 445, and 522B
are determined at 120 K and analyzed via the empirical harmonic–oscillator–stabilization–energy
and bond-length–alternation models, based on resonance theory.
Results from these analyses are used to rationalize the optoelectronic
properties of these coumarins, such as their UV–vis peak absorption
wavelength, molar extinction coefficient, and fluorescence quantum
efficiency. The specific molecular structural features of these four
coumarins and the effects on their optoelectronic properties are further
examined via a comparison with other similar coumarin derivatives,
including coumarins 314, 500, and 522. These findings are corroborated
by density functional theory (DFT) and time-dependent DFT calculations.
The structure–property correlations revealed herein provide
a foundation for the molecular engineering of coumarins with “dial-up”
optoelectronic properties to suit a given device application
Predicting Solar-Cell Dyes for Cosensitization
A major limitation of using organic
dyes for dye-sensitized solar
cells (DSCs) has been their lack of broad optical absorption. Cosensitization,
in which two complementary dyes are incorporated into a DSC, offers
a route to combat this problem. Here we construct and implement a
design route for materials discovery of new dyes for cosensitization,
beginning with a chemically compatible series of existing laser dyes
which are without an anchor group necessary for DSC use. We determine
the crystal structures for this dye series and use their geometries
to establish the DSC molecular design prerequisites aided by density-functional
theory and time-dependent density-functional theory calculations.
Based on insights gained from these existing dyes, modified sensitizers
are computationally designed to include a suitable anchor group. A
DSC cosensitization strategy for these modified sensitizers is predicted,
using the central features of highest-occupied and lowest-unoccupied
molecular orbital positioning, optical absorption properties, intramolecular
charge-transfer characteristics, and steric effects as selection criteria.
Through this molecular engineering of a series of existing non-DSC
dyes, we predict new materials for DSC cosensitization