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 design of multistate/multifunctional molecular systems arouses a lot of interest. Such compounds are able to commutate between two metastable states by the application of an external stimulation ...such as light, heat, protons, or electrons. In this context, we are interested in molecular switches based on indolino-oxazolidine (BOX) which is a relatively less-known sub-class of multimodal addressable units. Their particularity consists of the possibility to induce the opening/closing of the oxazolidine ring by using indifferently light, electrochemical, or acido-basic stimulation. Up to now, most of the reported systems based on BOX have allowed to modulate a molecular property but only between two discrete levels which can only be extended by their association with other classical switchable unit such as a dithienylethene unit. For this reason, we report here our effort to enhance the number of metastable states by simply connecting two identical BOX units by a bithiophene (BT) linker. The resulting system’s ability to switch between the three possible metastable states was investigated. Irrespective of the nature of the stimulation, full commutation of the system could be reached, but our work mainly revealed that the opening of both oxazolidine rings occurs in a stepwise manner. If this unreported selectivity upon a unique stimulus with two identical switchable units is observed irrespective of the stimulation, it must be pointed out that its efficiency depends on the nature of the latter. The direct stimulation with acid or light leads to the coexistence of the three different states of the system over a broad stimulation period. On the contrary, the indirect stimulation of BOX via an electromediated process due to the electroactivity of BT enhances the selective addressability between both identical BOX units.
Three addressable indolino-oxazolidine units connected through an isomerizable double bond to a substituted thiophene represent a smart example of a multiaddressable system whose reversible responses ...could be selectively activated on demand. Experimental and theoretical approaches to push forward the understanding of the system mechanism and set pathways to design optimized compounds for suitable application are here presented. NMR and UV–visible spectroscopies are used for structural and kinetic studies, while density functional theory (DFT) calculations pave the way to highlight energetic and electronic processes that are involved. Substitution and solvent effects toward the reactivity of the compounds are experimentally studied and combined with theoretical calculations. The most efficient and selective stimuli to travel between the four possible states resulting from the ring-opening of indolino2,1-boxazolidine (generally referenced as BOX) derivatives and the trans–cis isomerization of the ethylenic junction are elucidated.
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%).
The metastable trilacunary heteropolyoxomolybdate PMo
9
O
31
(py)
3
3−
-
{PMo
9
}
; py = pyridine) and the ditopic pyridyl bearing diarylethene (DAE) (C
25
H
16
N
2
F
6
S
2
) self-assemble
via
a ...facile ligand replacement methodology to yield the photo-active molecular capsule (PMo
9
O
31
)
2
(DAE)
3
6−
. The spatial arrangement and conformation of the three DAE ligands are directed by the surface chemistry of the molecular metal oxide precursor with exclusive ligation of the photo-active antiparallel rotamer to the polyoxometalate (POM) while the integrity of the assembly in solution has been verified by a suite of spectroscopic techniques. Electrocyclisation of the three DAEs occurs sequentially and has been investigated using a combination of steady-state and time-resolved spectroscopies with the discovery of a photochemical cascade whereby rapid photoinduced ring closure is followed by electron transfer from the ring-closed DAE to the POM in the latent donor-acceptor system on subsequent excitation. This interpretation is also supported by computational and detailed spectroelectrochemical analysis. Ring-closing quantum yields were also determined using a custom quantum yield determination setup (QYDS), providing insight into the impact of POM coordination on these processes.
The metastable trilacunary heteropolyoxomolybdate PMo
9
O
31
(py)
3
3−
; py = pyridine) and the ditopic pyridyl bearing diarylethene (DAE) (C
25
H
16
N
2
F
6
S
2
) self-assemble
via
a facile ligand replacement methodology to yield the photo-active molecular capsule (PMo
9
O
31
)
2
(DAE)
3
6
−
.
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
K
, (ii) the excited state complexation constant
K
*, (iii) the photoejection properties and (iv) the population of the triplet states from a singlet state
via
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
2+
cation from the site 1 but no photo-recapture was observed in the site 2 Aloïse
et al.
,
Phys. Chem. Chem. Phys
., 2016,
22
, 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.
This study provides a guide for the conception of efficient "Excited State Cation Transfer" photoswitches.
In this study, we examined the photophysical properties of an azacrown-Iridium(III) complex while focusing on its interactions with calcium ions (Ca 2+ ). We explored the dynamic processes within the ...complex combining time-dependent density functional theory (TDDFT) calculations and time-resolved spectroscopies. In the presence of Ca 2+ , the complex exhibits significant shifts in absorption and emission profiles, from 494 nm to 375 nm, aligning with theoretical predictions. Notably, we observed the ultrafast photo-ejection of Ca 2+ within 70 femtoseconds, followed by its recapture in 250 nanoseconds, revealing a 10-million-fold timescale difference between the two phenomena. These behaviors confirm the established photophysical properties of polypyridyl Iridium(III) complexes and their intrinsic sensitivity to their surrounding environment. Our comprehensive kinetic analysis highlights the azacrown moiety's competitive binding and photo-release capabilities, suggesting practical sensing applications. The versatile properties of these Iridium(III) complexes offer promising prospects for advanced optoelectronic devices, targeted imaging, stimuli-responsive materials, and biomedical ion sensors and delivery systems.
Les composés moléculaires étudiés présentent une fonction indolino-oxazolidine (Box) et une jonction éthylénique (lié à un groupement thiényle – Box simples) qui sont toutes deux commutables ...chimiquement ou photochimiquement entre deux états. Le suivi des réactions associées a été réalisé en solution par spectroscopie RMN 1H afin de caractériser les différents états de commutation de ces composés. L’ouverture de la fonction Box peut être provoquée par ajout d’acide ou par irradiation dans l’UV (chloroforme), et ce processus est réversible en présence de base. Quel que soit l’état de la Box, l’isomérisation trans cis de la jonction éthylénique est photochimique par irradiation à 436 nm alors que la réaction inverse est spontanée et thermique. Des composés comportant deux fonctions Box et deux jonctions éthyléniques liées à un groupement aromatique phényle ou bithiényle (BiBox) ont également été étudiés et des processus de commutation similaires ont été observés entre un nombre d’états supérieur du fait de la présence de quatre entités commutables. La commutation entre les différents états a donc été montrée et est déterminé le stimulus le plus adapté pour donner un été sélectivement et quasi quantitativement. Des calculs de chimie quantique de DFT et de TD-DFT ont permis de caractériser les structures moléculaire et électronique de chacun des états de commutation des Box simples ainsi que certains états des systèmes BiBox et de rationaliser certaines observations expérimentales. Des propriétés de fluorescence ont été observées et les spectres d’émission mesurés et les rendements quantiques de fluorescence calculés en fonction de l’état ouvert ou fermé de la (des) Box.
Molecular systems studied here present an indolino-oxazolidine (Box) moiety and an ethylenic junction (linked to a thienyl residue – Box simple) which are both chemically and photochemically switchable between two states. The switching reactions were followed in solution by 1H NMR spectroscopy in order to characterize the different metastable states. Opening of the Box moiety can be triggered upon acidification or by UV irradiation in chloroform and the reaction is reversible upon neutralization with base. Whatever the closed/open state of the Box moiety is, ethylenic junction trans cis isomerization is photochemically driven by 436 nm irradiation, whereas the reverse reaction is thermally spontaneous. Compounds with two Box moieties and two ethylenic junction linked together by a phenyl or bithienyl aromatic bridge (BiBox) have also been studied and similar switching behavior have been observed between much more states due to the presence of four switchable functions. Thus, the commutation between different states has been shown and most suitable stimulus to convert selectively and almost quantitatively from one state to another have been evidenced. Based on DFT and TDDFT methods, quantum chemistry calculations allowed to characterize molecular and electronic structures of the four switching states for Box simple systems and of some of BiBox and to rationalize some experimental observations. Fluorescence properties being surprisingly observed and so, then emission spectra and corresponding fluorescence quantum yields have been determined. The fluorescence data depend on the open/closed state of the Box moieties, allowing additional properties to these compounds.
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