6,6'-Biindeno[1,2-]fluorene: an open-shell indenofluorene dimer.

Nakano reported that the antiaromatic indenofluorene (IF) isomers are diradicaloid molecules having varying degrees of open-shell character, with indeno[1,2-]fluorene displaying a weaker diradical character index ( = 0.072). Unlike 6,12-trimethylsilylethynyl disubstituted [1,2-]IF, the 6,12-aryl disubstituted [1,2-]IF derivatives did not show any experimental evidence of diradical properties.

Reply to the Correspondence on "Visible Light-Switchable Chalcone-Flavylium Photochromic Systems in Aqueous Media".

In a Correspondence on our previous work, "Visible light-switchable chalcone flavylium photochromic systems in aqueous media" published in this journal in 2023, Pina et al. comment on certain aspects of our work, raising skepticism and questions about the switching of the chalcone-flavylium systems. We appreciate their comments and acknowledge the remarkable contribution of Pina and co-workers in this field.

Light-induced reversible switching of generation and extinction of an organic radical anion.

Radicals play a crucial role across various domains, ranging from serving as catalysts in chemical reactions to materials for spintronic applications. Currently, a major challenge for the chemists is the development of the next generation of organic radicals controllable by photons. To tackle this challenge, here we introduce a dyad system that combines a dimethyldihydropyrene (DHP) photochromic unit with a naphthalene diimide (NDI) moiety.

An Emission-Based Probe for the Detection and Quantification of DNA and RNA.

Sequence-independent detection of low concentrations of nucleic acids is important for applications in forensics and diagnostics. An emission-based probe for detecting and quantifying DNA and RNA utilizing a water-soluble dicationic tetraphenylethene (TPE) derivativewas developed. The recognition is based on the electrostatic and other non-covalent interactions between the phosphate backbone of nucleic acids and the cationic probe, which cause the restriction of rotation of the aryl units of the probe, ensuing in the enhancement of the fluorescence signal.

Cyano disubstituted tetrabenzoindeno[2,1-]fluorene: open-shell or closed-shell?

Organic diradicaloids have lately emerged as potential spintronic materials. We report the unprecedented synthesis of a near-IR absorbing indeno[2,1-]fluorene derivative that displays remarkably low LUMO (-4.15 eV) and a small HOMO-LUMO gap (0.

Tuning properties of functionalized azobenzene photoswitches through variation of substitution and their position.

This perspective article features the recent work published in this journal on functionalized azobenzene photoswitches, studied by Venkataramani and coworkers [Grewal, S. et al (2024) Photochem. Photobiol.

Light-driven modulation of electrical conductance with photochromic switches: bridging photochemistry with optoelectronics.

Photochromic conducting molecules have emerged because of their unique capacity to modulate electrical conductivity upon exposure to light, toggling between high and low conductive states. This unique amalgamation has unlocked novel avenues for the application of these materials across diverse areas in optoelectronics and smart materials. The fundamental mechanism underpinning this phenomenon is based on the light-driven isomerization of conjugated π-systems which influences the extent of conjugation.

Visible-light-switchable Chalcone-Flavylium Photochromic Systems in Aqueous Media.

The chalcone-flavylium photochromic system switches in aqueous media. However, the chalcone→flavylium conversion requires detrimental ultra-violet (UV) light for the switching which deters their applications in the biological domain. To address this issue, we have synthesized strategically modified chalcone scaffolds that can be reversibly switched to the flavylium forms with visible light ranging from 456 nm (blue) to 640 nm (red).

Stable Diradical on the Dimethyldihydropyrene Scaffold.

The diradical character in a molecular architecture can be customized primarily in two ways: first, by employing a quinoidal pro-aromatic system with net energy gained by aromatization that compensates for the energy required to generate the diradical species and, second, by employing an antiaromatic system having easily accessible triplet states that impart a diradical character. We have chosen a 14π aromatic framework, Boekelheide's dimethyldihydropyrene, and perturbed its aromaticity through the construction of its quinoidal form. The perturbed aromaticity was evident from the bond alteration in the X-ray diffraction structure, H nuclear magnetic resonance chemical shifts, and quantum chemical calculations.

Detection of Sialic Acid and Imaging of Cell-Surface Glycan Using a Fluorescence-SERS Dual Probe.

Sialic acid (SA) is an acidic monosaccharide present in the human brain and body fluids in the form of -acetylneuraminic acid. It is also a well-known cancer biomarker. For decades, it has remained a challenging task to design synthetic receptors for SA.

Highly Selective and Quantitative Point-of-Care Diagnostic Method for Adrenaline.

Adrenaline, also known as epinephrine, is a neurotransmitter/hormone that is an important target in diagnostics. Development of an effective method for detecting it in the presence of other neurotransmitters is a challenging task. The electrochemical and fluorescent techniques commonly used have low selectivity in distinguishing among catecholamines.

Morphology Tuning via Linker Modulation: Metal-Free Covalent Organic Nanostructures with Exceptional Chemical Stability for Electrocatalytic Water Splitting.

The development of synthetic routes for the formation of robust porous organic polymers (POPs) with well-defined nanoscale morphology is fundamentally significant for their practical applications. The thermodynamic characteristics that arise from reversible covalent bonding impart intrinsic chemical instability in the polymers, thereby impeding their overall potential. Herein, a unique strategy is reported to overcome the stability issue by designing robust imidazole-linked POPs via tandem reversible/irreversible bond formation.

Photoresponsive Small Molecule Enzyme Mimics.

Enzyme mimics emulate the catalytic activities of their natural counterparts. Light-responsive enzyme mimics are an emerging branch of biomimetic chemistry where the catalytic activities can be controlled reversibly by light. These light-responsive systems are constructed by incorporating a suitable photoswitchable unit around the active-site mimic.

Azobenzene-based Photochromic Delivery Vehicles for Ions and Small Molecules.

Molecular switches have been used as delivery vehicles for various molecular and ionic species. The ones that reversibly operate with light are arguably the best candidates for the purpose as they can be operated using light. The two states of these photoswitchable systems often possess remarkable differences in terms of their structural features and electronic properties.

Mimicking the Energy Funnel of the Photosynthetic Unit Using a Dendrimer-Dye Supramolecular Assembly.

Photosynthesis involves light-harvesting complexes where an array of antenna pigment channels the absorbed solar energy to the reaction centre of a photosystem. This work reports a supramolecular dendrimer-dye assembly that mimics the natural light-harvesting mechanism. A dendrimeric molecule based on two-fluorophores has been constructed with three coumarin units at the end of three long arms and a 7-diethylaminocoumarin unit at the interior.

Metal Ion Mediated Instant → Isomerization of Azobenzene Macrocycles in the Absence of Light.

The classical photoswitch azobenzenes reversibly interconvert between the - and the -isomers with light. Here, we report a pair of new macrocyclic azobenzenes characterized thoroughly by spectroscopic methods and single crystal X-ray diffraction structures, and one of the compounds displays a quantitative conversion of the - to the -form. These compounds, besides their normal photoswitching behavior, display an unusual instant switching of the -form to the -isomer in the presence of Cu ions in the dark under 273 K.

Light-Gated Modulation of Electronic Mobility of a Dihydropyrene-Based Photochromic Coordination Polymer.

Photo-induced modulation of electronic conductance has been achieved by employing an Ag-based two-dimensional coordination polymer (CP) having pyridine-functionalized photochromic dimethyldihydropyrene-cyclophanediene (DHP-CPD) π-switch. Both the coordination polymer and the organic photochromic core were characterized by single-crystal X-ray diffraction studies. The coordination polymer displayed an excellent conductance in the ON state of the switch in the closed form of DHP.

A Photoregulated Racemase Mimic.

The racemase enzymes convert L-amino acids to their D-isomer. The reaction proceeds through a stepwise deprotonation-reprotonation mechanism that is assisted by a pyridoxal phosphate (PLP) coenzyme. This work reports a PLP-photoswitch-imidazole triad where the racemization reaction can be controlled by light by tweaking the distance between the basic residue and the reaction centre.

Switching the recognition ability of a photoswitchable receptor towards phosphorylated anions.

An azobenzene based photoswitchable macrocyclic receptor displays different binding affinities in its E and Z forms towards various phosphorylated coenzymes under physiological conditions with remarkable selectivity for ATP in the E-form and selectivity towards GTP in the photoisomerized Z-form. Linear discriminant analysis clearly separated the analytes using the E-form. An application of this method enabled monitoring the progress of enzymatic phosphorylation using a tyrosine kinase enzyme.

Formation or Cleavage of Rings via Sulfide-Mediated Reduction Offers Background-Free Detection of Sulfide.

A set of three highly selective probes for sulfide detection has been developed. Two novel mechanistic strategies for the detection, including (a) transformation of a pro-fluorophore into an active fluorophore and (b) destruction of a fused ring to activate a fluorophore, have been explored. The structural features of the probes including azido groups ("active" and "latent") and leaving groups (with or without being attached to the fluorophore) have been investigated.

Modulation of Electronic Mobility of a One-Dimensional Coordination Polymeric Molecular Wire with Light.

Metal ions often influence the photoswitching efficiency of a photochromic system. This article reports a one-dimensional polymer having cyclic azobenzenes coordinated to silver ions that are bridged by nitrates. The coordination polymer (CP-2) displays a photoresponsive behavior.

Light triggered encapsulation and release of C with a photoswitchable TPE-based supramolecular tweezers.

Stimuli responsive hosts for C can control its binding and release on demand. A photoswitchable TPE based supramolecular host can encapsulate C in the Z-form with a markedly different visual change in the colour. In addition, the Z-1 bound C has been characterized by various spectroscopic methods and mass spectrometry.

A phototunable anion receptor for C-HX interactions with benzoate anions.

A supramolecular receptor consisting of two anthracene moieties with binding motifs for binding of benzoate anions is reported here. NMR studies indicate that the binding involves π-π interactions and CHX interactions. Upon exposure to >350 nm light, the receptor undergoes a [4 + 4] photoelectrocyclization restricting the access to the binding site for benzoate.

Reversible photoresponsive activity of a carbonic anhydrase mimic.

The carbonic anhydrase (CA) enzyme reversibly transforms carbon dioxide and water to a carbonate ion and a proton. Photoresponsive enzyme mimics, where the CA-activity can be turned on and off reversibly with light, have not been reported so far. We have designed an active site mimic that offers reversible control of the catalytic activity using light.

Formation of disulphide linkages restricts intramolecular motions of a fluorophore: detection of molecular oxygen in food packaging.

Reliable and easy detection of oxygen in food packaging without the aid of sophisticated instruments is highly coveted. A tetraphenylethene probe based on oxygen-mediated polymerization via the formation of disulfides causes restricted intramolecular rotation of the TPE phenyls resulting in a >100 fold enhancement of emission and thus detects O2 in food packages.