A Green-to-Near-Infrared Photoswitch Based on a Blended Subporphyrazine-Dithienylethene System

A subporphyrazine (SubPz)-dithienylethene (DTE) photochromic device with 1o and 1c states, was developed and characterized. In this device, the DTE unit can reversibly switch the SubPz absorbance from green to near-infrared [λmax (o/c) = 527 nm/740 nm], as well as the SubPz fluorescence and singlet oxygen quantum yields. The core of this design involves using a highly tunable SubPz chromophore that shares its quasi-isolated ethene moiety with a DTE photoswitch.

Recent update on the electroactive oligopyrrolic macrocyclic hosts with a Bucky-ball heart

Supramolecular chemistry is a multidisciplinary research area mostly associated with the investigation of host-guest interactions within intricate three-dimensional (3D) molecular architectures held together reversibly by various non-covalent interactions. Continuous efforts to develop such kinds of complex host-guest systems with designer oligopyrrolic macrocyclic receptors are a rapidly growing research domain, which is deeply involved in applied supramolecular chemistry research. These host-guest supramolecular complexes can be constructed by combining suitable electron-rich oligopyrrolic donors (as a host) with complementary electron-poor guests (as acceptors), held together by the ionic force of attraction triggered by intermolecular charge/electron transfer (CT/ET) transitions. Some of these resulting CT/ET ensembles are potential candidates for the construction of efficient optoelectronic materials, optical sensors, molecular switches, etc. In this Feature Article we aim to focus on these supramolecular ensembles composed by size and shape complementary electroactive oligopyrrolic molecular containers, which are suitable for spherical guest (e.g., buckminsterfullerene) complexation. We also provide a "state-of-the-art" overview on plausible applications of these particular host-guest systems. Our aim is to cover only specific electron-rich tetrathiafulvalene (TTF)-based oligopyrrolic receptors, e.g., TTF-calix[4]pyrroles, TTF-cryptands, TTF-porphyrins and exTTF-porphyrin-based molecular motifs reported to date, along with a brief outlining of their "functional behaviour" in materials chemistry research.

Organic-Inorganic Porphyrinoid Frameworks for Biomolecule Sensing

Porphyrinoids and their analogous compounds play an important role in biosensing applications on account of their unique and versatile catalytic, coordination, photophysical, and electrochemical properties. Their remarkable arrays of properties can be finely tuned by synthetically modifying the porphyrinoid ring and varying the various structural parameters such as peripheral functionalization, metal coordination, and covalent or physical conjugation with other organic or inorganic scaffolds such as nanoparticles, metal-organic frameworks, and polymers. Porphyrinoids and their organic-inorganic conjugates are not only used as responsive materials but also utilized for the immobilization and embedding of biomolecules for applications in wearable devices, fast sensing devices, and other functional materials. The present review delineates the impact of different porphyrinoid conjugates on their physicochemical properties and their specificity as biosensors in a range of applications. The newest porphyrinoid types and their synthesis, modification, and functionalization are presented along with their advantages and performance improvements.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Synthesis strategies for non-symmetric, photochromic diarylethenes

Diarylethenes (DAEs) represent an important class of photochromes with notable characteristics, like thermally irreversible photoisomerization and high fatigue resistance. Structural diversification of the DAE scaffold has enabled further refinement of photochromic properties and realization of new applications, ranging from advanced materials to tools for studying biological systems. In particular, methods for synthesizing non-symmetric DAE scaffolds, which are typically more challenging to synthesize than their symmetric counterparts, have grown over the past 20 years. These developments are surveyed in this review, with discussion of how access to these compounds has contributed to the improvement of photochromic properties and paved the way for exploring new applications of DAEs. First, non-symmetric DAE structures are classified and their uses and applications are overviewed. Subsequent sections discuss the main strategies that have been used to access non-symmetric DAEs with examples illustrating the impact of non-symmetric DAEs in the growing field of light-controlled molecular systems.

A Dynamic Hydrogen-Bonded Azo-Macrocycle for Precisely Photo-Controlled Molecular Encapsulation and Release

A light-responsive system constructed from hydrogen-bonded azo-macrocycles demonstrates precisely controlled propensity in molecular encapsulation and release process. A significant decrease in the size of the cavity is observed in the course of the E→Z photoisomerization based on the results from DFT calculations and traveling wave ion mobility mass spectrometry. These macrocyclic hosts exhibit a rare 2:1 host-guest stoichiometry and guest-dependent slow or fast exchange on the NMR timescale. With the slow host-guest exchange and switchable shape change of the cavity, quantitative release and capture of bipyridinium guests is achieved with the maximum release of 68 %. This work underscores the importance of slow host-guest exchange on realizing accurate release of organic cations in a stepwise manner under light irradiation. The light-responsive system established here could advance further design of novel photoresponsive molecular switches and mechanically interlocked molecules.

Hybrid organic–inorganic supramolecular systems based on a pyridine end-decorated molybdenum(ii) halide cluster and zinc(ii) porphyrinate

Herein, first examples of supramolecular coordination bonded hybrids of Mo(ii) cluster and zinc(ii) porphyrinates are reported.

Structure-function relationships of donor-acceptor Stenhouse adduct photochromic switches

The first in-depth, systematic study of the photoswitching properties of Donor-Acceptor Stenhouse Adducts (DASAs) is reported. Barbituric acid derived DASAs functionalised with 14 different amines ranging from dimethylamine to 4-methoxy-N-methylaniline were structurally characterised in solution using 1H and 13C NMR spectroscopy and, in eight cases, in the solid state by single crystal X-ray diffraction. The distribution of coloured and colourless isomers in the dark, their photostationary states under irradiation, apparent thermal half-lives, and fatigue resistance are systematically compared. A simple kinetic model is used to characterise photoswitching behaviour and reveals that minor structural modifications can significantly improve the photoswitching properties of DASA photochromes. These modifications result in excellent photoswitching properties for '1st generation' DASAs in chloroform, including exceptional fatigue resistance, opening the door for these photochromic molecules to find widespread applications.

A Dynamic and Responsive Host in Action: Light-Controlled Molecular Encapsulation

The rational design of a flexible molecular box, oAzoBox⁴⁺, incoporating both photochromic and supramolecular recognition motifs is described. We exploit the E↔Z photoisomerization properties of azobenzenes to alter the shape of the cavity of the macrocycle upon absorption of light. Imidazolium motifs are used as hydrogen‐bonding donor components, allowing for sequestration of small molecule guests in acetonitrile. Upon E→Z photoisomerization of oAzoBox⁴⁺ the guest is expelled from the macrocyclic cavity.

Self-assembled dimethyldihydropyrene-pyridyl substituted ligands with zinc(ii) meso-tetraphenylporphyrin via axial coordination

A series of dimethyldihydropyrene (DHP)-pyridyl photochromic derivatives has been synthesized and its photochemical behaviour characterized by spectroscopic and electrochemical methods.

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, the panels of which are based on the extended tetrathiafulvalene unit (exTTF). The unique combination of electronic and conformational features of this framework (i.e. high π-donating properties and drastic conformational changes upon oxidation) allows the reversible disassembly/reassembly of the redox-active cavity upon chemical oxidation/reduction, respectively. This cage is able to bind the three-dimensional B12 F12 (2-) anion in a 1:2 host/guest stoichiometry. The reversible redox-triggered disassembly of the cage could also be demonstrated in the case of the host-guest complex, offering a new option for guest-delivering control.

Light-Controlled Interconversion between a Self-Assembled Triangle and a Rhombicuboctahedral Sphere

Stimuli-responsive structural reorganizations play an important role in biological processes, often in combination with kinetic control scenarios. In supramolecular mimics of such systems, light has been established as the perfect external trigger. Here, we report on the light-driven structural rearrangement of a small, self-assembled Pd3L6 ring based on photochromic dithienylethene (DTE) ligands into a rhombicuboctahedral Pd24L48 sphere measuring about 6.4 nm across. When the wavelength is changed, this interconversion can be fully reversed, as confirmed by NMR and UV/Vis spectroscopy as well as mass spectrometry. The sphere was visualized by AFM, TEM, and GISAXS measurements. Due to dissimilarities in the photoswitch conformations, the interconversion rates between the two assemblies are drastically different in the two directions.