Photon-Working SwitchesProperties and Applications of Indolinooxazolidines as Photo-, Electro-, and Acidochromic Units

The aim of this chapter was to introduce the readers to indolinooxazolidines (IndOxa), a new family of molecular switches. First, in a short historical account their evolution is followed from their first appearance in the 1970s until today. The second section concentrates on the general structural features of the indolinooxazolidine motif, which are closely related to those of the spiropyrans. In the core of their chemistry lies the oxazolidine ring opening that is discussed in the following. Owing to the facility of the very same ring opening, they show chromophoric properties and can be addressed using different stimuli, such as light irradiation, change in electrical potential and pH. For this reason, the last three sections are devoted to provide a general understanding on their photo-, electro-, and acidochromic properties

The stepwise oxidation of indolino[2,1-b]oxazolidine derivatives

This work presents an original strategy to modulate the electrochemical properties of the indolino[2,1-b]oxazolidine core appropriately substituted in position 5 (para-substitution of the phenyl ring) by acceptor or donor groups (CHO, OMe, Me, F, H, Cl, Br). Supported by spectroelectrochemical experiments and confronted to electrochemical simulations, the stepwise oxidation of indolino[2,1-b]oxazolidine derivatives involves an electrochemical mechanism which depends on the para-substitution of the phenyl ring and leads to either the formation of a stable radical cation, the opening of the oxazolidine ring or an irreversible aryl C-C coupling

Silica-Mediated Synthesis of Indolinooxazolidine-Based Molecular Switches

A novel and convenient method for the synthesis of photochromic compounds is reported here. It is based on the use of commercially available untreated silica, as an efficient catalyst to perform the condensation between indolinooxazolidine derivatives and aromatic aldehydes under solvent-free conditions. The scope and limitations of this transformation were investigated and several novel photochromic indolinooxazolidines were synthesized. This methodology can also be applied to the synthesis of other photoactive compounds such as spiropyrans or spirooxazines. According to our working protocol the reaction did not require any solvent or additional reagents and gave the products within 10 min in isolated yields of up to 90%

Huge Electro-/photo-/acidoinduced Second-order Nonlinear Contrasts from Multiaddressable Indolinooxazolodine

In this work, linear and nonlinear optical properties of electro-/acido-/photoswitchable indolino[2,1-b]oxazolidine derivatives were investigated. The linear optical properties of the closed and open forms have been characterized by UV–visible and IR spectroscopies associated with DFT calculations. Nonlinear optical properties of the compounds have been obtained by ex situ and in situ hyper-Rayleigh experiments in solution. We show that protonated, oxidized, and irradiated open forms exhibit the same visible absorption and NLO features. In particular, the closed and open forms exhibit a huge contrast of the first hyperpolarizability with an enhancement factor of 40–45. Additionally, we have designed an original electrochemical cell that allows to monitor in situ the hyper-Rayleigh response upon electrical stimulus. We report notably a partial but good and reversible NLO contrast in situ during oxidation/reduction cycles. Thereby, indolinooxazolidine moieties are versatile trimodal switchable units which are very promising for applications in devices

Neutral versus polycationic coordination cages: a comparison regarding neutral guest inclusion

A neutral self-assembled container synthesized from a concave p-extended tetrathiafulvalene (exTTF) ligand and the cis-Pd(dctfb)2(cod) complex (dctfb = 3,5-dichloro-2,4,6-trifluorobenzene; cod = 1,5-cyclooctadiene) is described. This molecular host exhibits a good binding ability for fused polyaromatic substrates. The corresponding inclusion properties are compared with those of a previously described analogous octacationic cage, offering therefore the opportunity to address the effect of the cavity charge state over the binding of neutral molecules

Redox-Driven Transformation of a Discrete Molecular Cage into an Infinite 3D Coordination Polymer

Two M12L6 redox‐active self‐assembled cages constructed from an electron‐rich ligand based on the extended tetrathiafulvalene framework (exTTF) and metal complexes with a linear geometry (PdII and AgI) are depicted. Remarkably, based on a combination of specific structural and electronic features, the polycationic self‐assembled AgI coordination cage undergoes a supramolecular transformation upon oxidation into a three‐dimensional coordination polymer, that is characterized by X‐ray crystallography. This redox‐controlled change of the molecular organization results from the drastic conformational modifications accompanying oxidation of the exTTF moiety

Reversible Guest Uptake/Release by Redox-Controlled Assembly/Disassembly of a Coordination Cage

Controlling the guest expulsion process from a receptor is of critical importance in various fields. Several coordination-cages have been recently designed for this purpose, based on various types of stimuli to induce the guest release. Herein, we report the first example of a redox-triggered process from a coordination-cage. The latter integrates a cavity whose panels are based on the extended-tetrathiafulvalene unit. The unique combination of electronic and conformational features of this framework (i.e. high-p donating properties and drastic conformational changes upon oxidation) allows the reversible disassembling/reassembling of the redox-active cavity upon chemical oxidation/reduction respectively. This cage is able to bind the three-dimensional B12F122- anion in a 1:2 (host:guest) stoichiometry. The reversible redox-triggered disassembling of the cage could be also demonstrated in the case of the host-guest complex, offering a new option for guest delivering control

Dithienylethene-Based Gated Ambichromic Dyads

A set of dithienylethene (DTE)-based ambichromic dyads containing an acido-, photo-, and electrosensitive indolino[2,1-b]oxazolidine (BOX) unit displays gated photochromism. Ring opening of BOX prevents photoinduced electrocylization between open and closed forms of DTE. The photochromic performances are regenerated by two different pathways. NMR and electrochemical studies evidence interactions between indolenium and phenyl–thienyl sidearms

Controlling the Host-Guest Interaction Mode through a Redox Stimulus

A proof-of-concept related to the redox-control of the binding/releasing process in a host-guest system is achieved by designing a neutral and robust Pt-based redox-active metallacage involving two extended-tetrathiafulvalene (exTTF) ligands. When neutral, the cage is able to bind a planar polyaromatic guest (coronene). Remarkably, the chemical or electrochemical oxidation of the host-guest complex leads to the reversible expulsion of the guest outside the cavity, which is assigned to a drastic change of the host-guest interaction mode, illustrating the key role of counteranions along the exchange process. The reversible process is supported by various experimental data (1 H NMR spectroscopy, ESI-FTICR, and spectroelectrochemistry) as well as by in-depth theoretical calculations performed at the density functional theory (DFT) level