Two phenothiazine-based electroactive compounds were synthesized by Buchwald-Hartwig cross-coupling reaction. The compounds consist of pyridine- or benzonitrile accepting moiety and phenothiazine donor fragments linked through tertiary amino linkage. The resulting electroactive compounds showed high thermal stability with 10% weight loss temperatures of 270 and 308 oC. Both the compounds showed reversible oxidation after repeated scans of cyclic voltammetry. Experimental results in combination with the outcomes of TD-DFT calculations, were employed to examine the emission nature of the target compounds. By demonstrating the correct choice of acceptor moiety and linking topology, the synthesized compounds were found to be emitters exhibiting efficient RTP. With emission lifetime reaching 26.04 ms and spin-orbit coupling value of the triplet states with the singlet ground state of 18.72 cm-1, the radiative recombination of the triplet state is ensured. Having lifetimes of 26 ms and strong sensitivity to oxygen, the benzonitrile-containing phenothiazine derivative demonstrated fast oxygen response with the quenching constant of 4.97*10-4 ppm-1 at low oxygen concentrations that is comparable to the corresponding characteristics of reported RTP-based sensors.

Small organic molecules absorbing and emitting in the shortwave infrared (SWIR, 1000-2000 nm) region are desirable for biological imaging applications due to low auto-fluorescence, reduce photon scattering, and good tissue penetration depth which allows for in vivo imaging with high resolution and sensitivity. Si-substituted xanthene-based fluorophores with indolizine donors have demonstrated some of the longest wavelength absorption and emission from organic dyes. This work seeks to compare an indolizine heterocyclic nitrogen with dimethyl aniline nitrogen donors on otherwise identical Si-substituted xanthene fluorophores via optical spectroscopy, computational chemistry and electrochemistry. Three donors are compared including an indolizine donor, a ubiquitous dimethyl aniline donor, and a vinyl dimethyl aniline group that keeps the number of π-bonds consistent with indolizine. Significantly higher quantum yields and molar absorptivity are observed in these studies for a dimethylamine-based donor relative to a simple indolizine donor absorbing and emitting at similar wavelengths (~1312 nm emission). Substantially longer wavelengths are obtainable by appending aniline-based groups to the indolizine donor (~1700 nm) indicating longer wavelengths can be accessed with indolizine donors while stronger emitters can be accessed with anilines in place of indolizine.

Triplet-triplet annihilation upconversion (TTA-UC) has made significant progress in recent years in several key applications, including solar energy harvesting, photocatalysis, stereoscopic 3D printing, and disease therapeutics. In TTA-UC research, photosensitizers serve the vital function of harvesting low-energy photons. The photophysical characteristics of photosensitizers, including absorbance, triplet state quantum yield, triplet state energy level, triplet state lifetime, etc., determine the performance of TTA-UC. Thus, the study of photosensitizers has been a key aspect of TTA-UC. In recent years, multi-resonance thermally activated delayed fluorescence (MR-TADF) molecules have received extensive attention due to their excellent photophysical properties and electroluminescent device performance. MR-TADF molecules not only present a narrow energy gap between the singlet and triplet excited states, but also have stronger absorption and better wavelength regulation than conventional TADF molecules. Nowadays, the preliminary attempts in TTA-UC using MR-TADF molecules as photosensitizers have resulted in the development of green to ultraviolet, blue to ultraviolet, and even near-infrared to blue emission. This concept will summarize the research progress of MR-TADF molecules as photosensitizers in TTA-UC, analyzing the challenges and giving possible solutions. Finally, we prospect the future development of MR-TADF molecules as photosensitizers, including the molecular design as well as the possible application areas.

A series of C-8 substituted indeno[1,2-g]coumarin-based photoremovable protecting groups (PPGs) were synthesized. para-Substituted benzoic acids were employed as leaving groups to evaluate their photolytic efficiency. Substitution of phenyl groups was proved to have negative impacts on photochemical properties of the PPGs, including but not limited to: retarded photolysis course, decreased uncaging quantum yield, and unsatisfactory cargo release yield. Electron-donating diethylamino substituted PPG 3d, a structural analogue of the widely used 7-diethylaminocoumarin PPG (DEACM), exhibited red-shifted absorption maximum and improved optical properties. Photochemical characterization revealed that PPG 3d not only showed comparable photolytic efficiency to DEACM at 365 nm and 405 nm, but also demonstrated superior sensitivity towards 465 nm wavelength, to which DEACM is unable to absorb and therefore, non-responsive. The >450 nm photosensitivity makes 3d a complement to DEACM for long wavelength excitation and a promising PPG for biological applications.

The influence of activation as key parameter for oxygen sensing by luminescent metal-organic frameworks has been investigated and quantified for the archetype MOF-76(Eu). Activation at different conditions (regarding temperature and solvent-exchange for distinct vacuum pressure and heating time), shows an influence on the overall quenching, response time and cyclability due to different pore accessibility and surface area and therefore on the overall performance of the sensor. The optical sensing process is based on luminescence quenching, analyzed from high vacuum (10−7 bar) to dosing oxygen from 0.01 bar to 1 bar. Strong influence of the different activation parameters is observed, as MOF-76(Eu) activated at 50 °C shows some quenching of the luminescence intensity within 30 min, while methanol-exchange and subsequent activation at 250 °C leads to a quenching rate of 98.6%. In addition, the sensor response occurs more than 1000 times faster within 0.2 s. These results correlate well with physisorption data, which reveal a significant change in porosity and surface area according to the degree of activation. For a better understanding of the involved processes, adsorption isotherms were recorded, surface areas determined and correlated to the photophysical parameters, including Stern-Volmer kinetics and cycling experiments for the differently activated MOF sensors

Abstract: Mesoporous silica (SBA-15) synthesized hydrothermally followed by calcination and then functionalization with 3-(trimethoxysilyl)-1-propanethiol through surface grafting. The thiol moiety of the grafted ligand is utilized for uniform anchoring the cadmium into the channels of the material. The synthesised material was subjected for its photo catalytic applications after characterization through standard characterization protocol. The synthesised SAB-15, ligand modified SBA-15-S and Cd loaded SAB-15-CdS were characterized through standard characterization protocol like   powder XRD, FT-IR, UV-DRS,  MAS NMR, N2 sorption, FE-SEM, HR-TEM and TG-DTA studies. After successful characterization the screening of the catalyst was carried out on a model reaction involving photo catalytic cleavage of α-O-4 aryl ether linkage present in benzyl phenyl ether, which is an important lignin model compound. The catalyst exhibited good efficiency along with the selectivity for desired monoaromatic platform chemicals. The synthesized catalyst was also carried out for the photo catalytic depolymerization of alkali lignin at the optimized reaction conditions which further showed the promising results for getting value added chemicals from lignin. The reaction products were characterized by using Gas chromatography-mass spectrometry (GC-MS) techniques.

Molecular solar thermal energy storage (MOST) based on photoisomerization represents a novel approach for the capture, conversion, and storage of solar energy. Azo photoswitches can store energy by isomerization from their thermodynamically stable E isomers to higher energy metastable Z isomers. Enhancing the energy density through molecular structural design represents a central research focus in the field of MOST. A straightforward approach to enhance the energy density is to design multi-azo photoswitches. This allows multiple azobenzene units to share a common framework while keeping the molecular weight as small as possible. In particular, when two azobenzene units are connected via a phenyl ring in a meta orientation, it facilitates efficient isomerization, thereby maximizing the energy density of the azo photoswitches (392 J g−1). This paper provides a brief overview of the development of multi-azo photoswitches and highlights their outstanding performance as a MOST system. It also offers prospects for their future advancements in the field. We propose that, to further improve the energy density of multi-azo photoswitches, one approach is to design wide spectrum of light photoisomerization of multi-azo photoswitches. Additionally, introducing photo-induced phase changes to multi-azo photoswitches enables the simultaneous storage of both photon energy and ambient heat.

Genetically encoded unnatural amino acids are useful tools for controlling protein function, but options for sequential activation of proteins using light as a trigger are limited. Here, we report the genetic encoding of two new photocaged lysine derivatives for activation of protein function, such as protein translocation and bioluminescence, with two different wavelengths of light and/or different durations of light exposure.

Abstract

Genetically encoded unnatural amino acids are versatile tools for controlling protein function, but options for regulating multiple proteins in a single experiment are limited. Here, we report the genetic encoding of two new photocaged lysine derivatives, 1-(2-nitrophenyl)-ethyl lysine and nitrodibenzylfuranyl lysine, for sequential light-activation of protein function in live cells. Nitrodibenzylfuranyl (NDBF) caging groups have a redshifted absorbance maximum and high sensitivity to light compared to the 1-(2-nitrophenyl)-ethyl group (NPE), enabling selective decaging and protein activation. We characterized the responses of these new caged amino acids by optically triggering nuclear localization and firefly luciferase activity. The ability to selectively activate distinct proteins through simple light titration makes this a useful approach with broad applications.

Isotonitazene belongs to a potent class of m-opioid receptor (µOR) ligands, known as nitazenes. The lack of knowledge surrounding this agonist and others in its class has sparked thorough re-investigations. To aid in these investigations, the purportedly covalent yet underexplored nitazene BIT was biochemically re-evaluated in this work, along with a newly synthesized analogue, Iso-BIT. Moreover, in the pursuit of understanding the mechanism, function, and interactions of µOR, this study involved developing photoswitchable derivatives of nitazene as potential probe molecules. Converting known ligands into azo-containing photoswitchable derivatives offers the opportunity to modulate ligand structure with light, allowing for photocontrol of compound activity. While photocontrol of µOR activity could not be entirely achieved, photophysical evaluation of these arylazobenzimidazole derivatives revealed a novel photoswitch scaffold that responds to visible light. Furthermore, azo-containing 2e and 3e emerged as promising nitazene derivatives that were able to form an exceptionally high fraction of covalent-ligand receptor complexes with wild-type µOR at physiological pH.

Recent research enhanced our understanding of perylene diimides (PDIs), especially their fluorescence and photothermal properties. Interplay between radiative and nonradiative transitions controls emission and heat generation. This review explores effective integration of these processes through molecular design within the PDI framework. It comprehensively discusses manipulating PDI structures for fluorescence and photothermal applications.

Abstract

Perylene diimides (PDIs) have received considerable attention as a versatile class of functional dyes owing to their flexible reaction sites and remarkable stability. Recent advances have enhanced our understanding of the fluorescence and photothermal conversion properties of PDI molecules. The interplay between radiative and nonradiative transitions controls the emission and heat generation processes in these molecules. This comprehensive overview summarizes the recent strategies for manipulating the structures of PDI molecules for fluorescence and photothermal conversion applications. Additionally, challenges and potential solutions associated with the usage of fluorescent and photothermal PDI molecules are discussed.