Combining different molecular switching functions in a single molecule is a simple strategy to develop commutable molecules featuring more than two commutation states. The present study reports on ...two molecular systems consisting of two indolino-oxazolidine (Box) moieties connected to an aromatic bridge (phenyl or bithiophene) by ethylenic junctions. Such systems, referenced as BiBox, are expected to show up multiaddressable and multiresponsive behaviors. On one hand, the oxazolidine ring opening/closure of Box moieties can be addressed by chemical stimuli, and on the other hand, the trans-to-cis isomerization of the ethylenic junctions is induced by visible light irradiation (with a thermal back conversion). NMR and UV–visible spectroscopies allowed to characterize up to nine out of the ten theoretically expected commutation states as well as to measure the kinetics of the interconversions. Also, steady state fluorescence spectroscopy measurements highlighted the strong influence of the open/closed states of the Box moieties on their emission properties.
The understanding of the intimate electronic processes in photochromes is essential to optimize the properties of light-controllable devices. For one of the most studied classes of molecular ...switches, namely, dithienylethenes, the relative efficiencies of the normal and inverse structures remained puzzling. Indeed, despite a larger ratio of the active antiparallel conformers for the latter, the quantum yields of cyclization of inverse dithienylethenes do not exceed those of its normal counterpart. In the present contribution, we provide the first explanation of this experimental outcome using multireference ab initio quantum chemistry. We demonstrate the existence of a fluorescent intermediate on the S1 state of the inverse system that generates a photochemically unreactive conformation in the ground state. This study paves the way toward a rational development of efficient molecular photochromes presenting a photon-quantitative response.
We report a QM (TD-DFT) and QM/QM' (ONIOM) study of the modulation of emission in a series of thiazolo5,4,bthieno3,2-epyridine (TTP) derivatives Huang et al., J. Mater. Chem. C, 2017, 14, 3456. By ...computing the excitation energy transfer couplings and the Huang-Rhys (HR) factors, we rationalize the aggregation-caused quenching (ACQ) observed for the parent molecule and the crystallization-induced emission (CIE) observed for the derivatives presenting intra-molecular H-bonding. We also show that the CIE strategy relying on the rigidification of the arch-bridge-like stator should be considered with caution since it can promote the energy dissipation through vibrational motions.
The structural evolution as a function of temperature of a supramolecular copolymer assembly based on multiple hydrogen bonds has been investigated. Ureidopyrimidinone functionalized semi-crystalline ...poly(ethylene-co-butylene) (PEB-(L-UPy)2) has been characterized by means of in situ WAXS and SAXS experiments. The crystallinity and the nature of crystal forms are associated to the ethylene sequences. Special attention has been paid to the impact of the hydrogen bonding network on the structural arrangements, by comparison to the unfunctionalized PEB. The presence of crystalline domains of in-plane arrangement between neighboring UPy dimers is detected by WAXS up to 80 °C. The SAXS data reflect the presence of L-UPy aggregates stable on the whole temperature range. The correlation of these UPy-based aggregates is effective until the PEB crystal melting temperature (Tm). Beyond Tm, the increase of the macromolecular mobility reduce the number of domains in interaction and, in consequence, implies a decorrelation of the aggregates.
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•Synthesis of ureidopyrimidinone functionalized semi-crystalline poly(ethylene-co-butylene).•WAXS structural characterization of the copolymer crystal forms.•Combined SAXS/WAXS investigation of the multi-scale arrangements of the supramolecular assembly as a function of temperature.
Photonastic materials present a directional and repeatable deformation of the material shape due to transduction from light energy to mechanical energy. Among these materials, light-responsive ...polymers, composed of photochromic molecules embedded in a polymer matrix, are of high interest. The present work aims at laying the foundation stone of the modeling of the photomechanical behavior of such systems by proposing a computational strategy that is able to investigate (i) the impact of the polymer matrix on the photochromic properties of a dithienylethene (DTE) switch and (ii) the impact of the photochromic reaction on the polymer environment. Contrary to previous approaches, the present model is able to propose a realistic arrangement of the photochrome embedded in the polymer film, thanks to the adaptation of the so-called “controlled-like polymerization algorithm” Lemarchand, C. A. ; J. Chem. Phys. 2019, 50, 224902 . Our strategy relies on molecular dynamics (MD) simulations and time-dependent density functional theory (DFT) calculations. Careful analysis of MD trajectories and comparison with simulations in solution have shown the rigidification of the DTE molecule due to the presence of the polymer chains, which hindered the interconversion between the DTE open-form isomers and can probably modify the photocyclization quantum yield. Besides, the UV–vis absorption properties of the DTE open-form isomers are more impacted by the polymer embedding than its closed-form counterpart. Concerning the impact of the photoreaction on the polymer matrix, the time evolution of the pressure tensor and of the atomic displacements in the matrix have shown that (i) the cyclization reaction has a negligible impact; (ii) the cycloreversion reaction induces a locally large and anisotropic pressure increase and leads to a collective displacement of the polymer matrix away from the reactive center; and (iii) the characteristic time scale associated with these coupled processes is below 1 ps. Therefore, the two processes involved in photonastic motions, namely, the photoreaction and the relaxation of the polymer matrix after the photoswitch structural change, cannot be decoupled.
Photodynamics and excited-state intramolecular proton transfer (ESIPT) of N-(3,5-ditert-butylsalicylidene)-4-aminopyridine (4P) and N-(3,5-ditert-butylsalicylidene)-2-aminopyridine (2P) are studied ...by steady-state and transient optical spectroscopy in solution and solid state (microcrystalline powder). These two compounds are representative of anils Classes A and B, respectively. The results confirm that in solution both compounds have a similar dynamic behavior: upon excitation at 390 nm, ESIPT leads to different cis-keto* fluorescent species which relax to the photochromic trans-keto photoproduct within a few tens of picoseconds. Furthermore, for the first time, picosecond data are recorded for the two classes of anils in the solid state: in 2P, two cis-keto* fluorescent excited state species (23 and 250 ps lifetime) are relaxing exclusively to the cis-keto ground state, whereas in 4P, a single cis-keto* fluorescent species is observed which leads to the trans-keto photoproduct in 250 ps via an intermediate metastable species.
A dithienylethene (DTE) photochromic compound functionalized by ureidopyrimidinone (UPy) quadruple hydrogen bonding blocks was synthesized by Takeshita and coworkers Takeshita
et al.
,
Chem. Commun.
..., 2005, 761 in order to form a light-responsive supramolecular self-assembling system. In solution, the formation of supramolecular assemblies was only observed for one DTE isomer, namely the closed-form isomer. To rationalize this experimental finding, with the help of Molecular Dynamics (MD) and (time-dependent) DFT calculations, the behaviour of open-form and closed-form monomers, dimers, hexamers and π-stacked dimers in solution is investigated. Our simulations show that, for the open-form oligomers, the progression of the supramolecular assembly is hindered due to (i) the possible formation of a very stable cyclic dimer for the open-form parallel isomer, (ii) the relative flexibility of the open-form oligomers compared to their closed-form counterparts, and (iii) the possible existence of π-stacked dimers that constitute bottlenecks blocking the progression of the supramolecular self-assembly.
The behaviour of light-responsive supramolecular assemblies is rationalized with the help of molecular dynamics and TD-DFT calculations.
A new class of photoswitches and the corresponding elementary photoinduced reaction, the so-called Excited-State Cation Transfer (ESCT), are investigated. This reaction relies on an intramolecular ...photo-release/photo-complexation of cation: after irradiation, the cation is translocated from a complexation site 1 to a site 2 during the excited state lifetime. Our purpose is thus to develop a computational strategy based on Density Functional theory (DFT) and its time-dependent counterpart (TD-DFT) to improve the different properties of the ESCT photoswitches, namely (i) the ground state complexation constant
, (ii) the excited state complexation constant
*, (iii) the photoejection properties and (iv) the population of the triplet states from a singlet state
intersystem crossing to increase the lifetime of the excited state. In this work, we are interested in optimizing the ESCT properties of a betaine pyridinium chromophore substituted by a 15-aza-5-crown, that was previously shown to efficiently photoeject a Ca
cation from the site 1 but no photo-recapture was observed in the site 2 Aloïse
,
., 2016,
, 15384. To this purpose, we have investigated the impact of the modification of the site 1 on the ESCT properties by introducing different substituents (EDG groups, halogen atoms) at different positions. So far, promising systems have been identified but a simultaneous improvement of all the ESCT photoswitches properties has yet not been achieved.
In the context of designing efficient photocontrolled ion-release systems, we propose a ”simple” computational strategy able to predict the cation photoejection. Our strategy is based on TD-DFT ...calculations and the analysis of the charge transfer (CT) parameters of the excited states that can be populated for a given excitation wavelength, in the Franck–Condon region.
With the help of CT descriptors (the variation of the electronic density, the so-called DCT index and the variation of natural population analysis NPA charges), we aim to identify the CT states presenting a depletion of electronic density on the complexation site after excitation. If the loss of electronic density is large enough in the cation binding site, the population of such a state should be the first step of the mechanism leading to the cation photorelease.
We test this strategy on ReAZBAP+-Mn+ (Mn+ = Li+, Na+, Mg2+, Ca2＋, Ba2+) and ReAZAT+-Ba2+ systems, a series of complexes synthesized and studied by Moore and co-workers Lewis et al. (2004). We show that our first-order approach that does not take into account the complex excited-state decay routes, is able to correctly predict the photorelease properties with a success rate of ca. 80 percent. This method should thus be considered as a valuable tool in the framework of the in silico design of light-controlled ion release.
•This study provides a guide for the synthesis of photocontrolled ion-release systems.•A simple computational strategy able to predict the cation photoejection is proposed.•This method relies on the charge transfer parameters of the excited states.•This method can correctly predict the photorelease properties (success rate: 80%).
•Unexpected photomechanical effects reported for a well-known photochromic diarylethene after thermal amorphization
The photomechanical properties of the photochromic ...1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluorocyclopentene (DTE) crystals, largely documented since the discovery by Irie et al. of its reversible photoswitching of crystallographic plane morphology, is renewed with a novel approach consisting on suppressing gradually dynamical effects through thermal amorphization. In the crystalline case, the reversibility of UV/Visible induced plastic deformations have been observed as expected. In addition, a number of large jumps for both cycles are reported for the first time for this molecule in contrast to being observed only during the first UV irradiation cycle for other DTEs. In the amorphous case, several striking results have been obtained: (i) the still present reversible photoinduced plastic deformations mimicking the crystalline case are interpreted in terms of apparent polyamorphism; (ii) the total vanishing of the jumps brings the evidence of the crucial role of the crystallinity for the propelling surface in contact with the substrate; (iii) the discovery of a never reported material jump during the first visible cycle. This last result is rationalized combining two features –a thermal one, a glass transition temperature very close to the room temperature (Tg ≈ 34°C) and –a photochemical one, an inefficient photoreversion allowing the other vibrational relaxation pathway to proceed inducing the required temperature rise to overpass the phase transition (Solid → Liquid) responsible for the jump.
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