Visible‐Light‐Mediated Thiol‐Ene Hydrogelation Using Eosin‐Y as the Only Photoinitiator

The utility of visible‐light‐mediated polymerization in tissue engineering has been limited due to the necessary use of potentially cytotoxic coinitiator and comonomer. Here, we report a visible‐light‐mediated thiol‐ene hydrogelation scheme using eosin‐Y as the only photoinitiator. Under visible light exposure, rapid and highly tunable step‐growth gelation is achieved using PEG‐norbornene and a model cross‐linker dithiothreitol. In addition to investigating the gelation kinetics and properties of thiol‐ene hydrogels formed by this new gelation scheme, we also report high cytocompatibility of these hydrogels using human mesenchymal stem cells (hMSCs) and pancreatic MIN6 β‐cells.     

Tunable Water‐Soluble Supramolecular Polymers by Visible‐Light‐Regulated Host–Guest Interactions

The development of artificial self‐assembling systems with dynamic photo‐regulation features in aqueous solutions has drawn great attention owing to the potential applications in fabricating elaborate biological materials. Here we demonstrate the fabrication of water‐soluble cucurbit[8]uril (CB[8])‐mediated supramolecular polymers by connecting the fluorinated azobenzene (FAB) containing monomers through host‐enhanced heteroternary π–π stacking interactions. Benefiting from the unique visible‐light‐induced E→Z photoisomerization of the FAB photochromophores, the encapsulation behaviors between the CB[8] macrocycle and the monomers could be regulated upon visible light irradiation, resulting in the depolymerization of such CB[8]‐mediated supramolecular polymers.     

Visible‐Light‐Promoted Generation of α‐Ketoradicals from Vinyl‐bromides and Molecular Oxygen: Synthesis of Indenones and Dihydroindeno[1,2‐c]chromenes

Ortho‐alkynylated α‐bromocinnamates can be converted by a visible‐light‐mediated photocascade reaction with molecular oxygen into either indenones or dihydroindeno[1,2‐c]chromenes. The one‐step process features key photochemical steps, that is, the initial activation of vinyl bromides through energy transfer to give α‐ketoradicals in a reaction with molecular oxygen, followed by α‐oxidation of an arene moiety by 6‐π electrocyclization, and subsequent hydroxylation by an electron‐transfer process from the same photocatalyst leads to the dihydroindeno[1,2‐c]chromenes.     

Vortex‐Pattern Self‐Assembly in Mn‐Doped ZnSe Nanorods

Spontaneous patterning of anisotropic nanostructures into ordered assemblies remains a challenging quest, which requires controlled innovative approaches. One way to achieve such ordering of 1D nanorods is by manipulating the varieties of interactions (attractive and repulsive forces) present in colloidal solutions of anisotropic nanocrystals. The other ingenuous pathway is solvent‐evaporation‐mediated self‐organization of the 1D nanorods. By following the second protocol, we have achieved exclusive pillar self‐assembled patterns of visible‐light‐emitting Mn‐doped ZnSe nanorods. The nanorods also exhibit intriguing vortex patterning observed by directional solvent evaporation from the nanorod solution. The effect of solvent evaporation to generate such unique morphologies on the TEM grid is discussed and the reported procedure to obtain the assembled patterns of visible‐light‐emitting, doped nanorods might be useful for future technological applications.     

Preparation of pyrrolo[2,1,5‐cd]indolizine Derivatives by intramolecular condensation of 3‐acyl‐5‐methylindolizines

An efficient two step route has been developed to synthesize pyrrolo[2,1,5‐cd]indolizine derivatives. The reaction sequence proceeds via preparation of 3‐acyl‐5‐methylindolizines followed by an intramolecular condensation. The procedures were carried out under convenient conditions and gave the products in high yields. It could be expected to be used to prepare a broad range of potentially interesting pyrrolo[2,1,5‐cd]indolizine derivatives.     

Visible‐Light‐Driven Aza‐ortho‐quinone Methide Generation for the Synthesis of Indoles in a Multicomponent Reaction

A visible‐light‐driven radical‐mediated strategy for the in situ generation of aza‐ortho ‐quinone methides from 2‐vinyl‐substituted anilines and alkyl radical precursors is described. This process enables an efficient multicomponent reaction of 2‐vinylanilines, halides, and sulfur ylides, and has a wide substrate scope and good functional group tolerance. Treatment of the cycloaddition products with a base leads to densely functionalized indoles in a single‐flask operation.     

Photochemical Synthesis of Complex Carbazoles: Evaluation of Electronic Effects in Both UV‐ and Visible‐Light Methods in Continuous Flow

An evaluation of both a visible‐light‐ and UV‐light‐mediated synthesis of carbazoles from various triarylamines with differing electronic properties under continuous‐flow conditions has been conducted. In general, triarylamines bearing electron‐rich groups tend to produce higher yields than triarylamines possessing electron‐withdrawing groups. The incorporation of nitrogen‐based heterocycles, as well as halogen‐containing arenes in carbazole skeletons, was well tolerated, and often synthetically useful complementarity was observed between the UV‐light and visible‐light (photoredox) methods.     

Visible‐Light‐Excited Room‐Temperature Phosphorescence in Water by Cucurbit[8]uril‐Mediated Supramolecular Assembly

Solid‐state materials with efficient room‐temperature phosphorescence (RTP) emissions have found widespread applications in materials science, while liquid or solution‐phase pure organic RTP emission systems has been rarely reported, because of the nonradiative decay and quenchers from the liquid medium. Reported here is the first example of visible‐light‐excited pure organic RTP in aqueous solution by using a supramolecular host‐guest assembly strategy. The unique cucurbit[8]uril‐mediated quaternary stacking structure allows tunable photoluminescence and visible‐light excitation, enabling the fabrication of multicolor hydrogels and cell imaging. The present assembly‐induced emission approach, as a proof of concept, contributes to the construction of novel metal‐free RTP systems with tunable photoluminescence in aqueous solution, providing broad opportunities for further applications in biological imaging, detection, optical sensors, and so forth.     

Deaminative Strategy for the Visible‐Light‐Mediated Generation of Alkyl Radicals

A deaminative strategy for the visible‐light‐mediated generation of alkyl radicals from redox‐activated primary amine precursors is described. Abundant and inexpensive primary amine feedstocks, including amino acids, were converted in a single step into redox‐active pyridinium salts and subsequently into alkyl radicals by reaction with an excited‐state photocatalyst. The broad synthetic potential of this protocol was demonstrated by the alkylation of a number of heteroarenes under mild conditions.     

Cytotoxicity of All‐Trans‐Retinal Increases Upon Photodegradation†

All‐trans‐retinal (AtRal) can accumulate in the retina as a result of excessive exposure to light. The purpose of this study was to compare cytotoxicity of AtRal and photodegraded AtRal (dAtRal) on cultured human retinal pigment epithelial cells in dark and upon exposure to visible light. AtRal was degraded by exposure to visible light. Cytotoxicity was monitored by imaging of cell morphology, propidium iodide staining of cells with permeable plasma membrane and measurements of reductive activity of cells. Generation of singlet oxygen photosensitized by AtRal and dAtRal was monitored by time‐resolved measurements of characteristic singlet oxygen phosphorescence. Photodegradation of AtRal resulted in a decrease in absorption of visible light and accumulation of the degradation products with absorption maximum at ～330 nm. Toxicity of dAtRal was concentration‐dependent and was greater during irradiation with visible light than in dark. DAtRal was more cytotoxic than AtRal both in dark and during exposure to visible light. Photochemical properties of dAtRal indicate that it may be responsible for the maximum in the action spectra of retinal photodamage recorded in animals. In conclusion, photodegradation products of AtRal may impose a significant threat to the retina and therefore their roles in retinal pathology need to be explored.     

Visible‐Light‐Mediated Metal‐Free Synthesis of Trifluoromethylselenolated Arenes

The first visible‐light‐mediated synthesis of trifluoromethylselenolated arenes under metal‐free conditions is reported. The use of an organic photocatalyst enables the trifluoromethylselenolation of arene diazonium salts using the shelf‐stable reagent trifluoromethyl tolueneselenosulfonate at room temperature. The reaction does not require the presence of any additives and shows high functional‐group tolerance, covering a very broad range of starting materials. Mechanistic investigations, including EPR spectroscopy, luminescence investigations, and cyclic voltammetry allow rationalization of the reaction mechanism.     

Visible‐Light‐Mediated Chan–Lam Coupling Reactions of Aryl Boronic Acids and Aniline Derivatives

The copper(II)‐catalyzed aerobic oxidative coupling reaction between aryl boronic acids and aniline derivatives was found to be improved significantly under visible‐light‐mediated photoredox catalysis. The substrate scope of this oxidative Chan–Lam reaction was thus expanded to include electron‐deficient aryl boronic acids as viable starting materials.     

Arenophile‐Mediated Dearomative Reduction

A dearomative reduction of simple arenes has been developed which employs a visible‐light‐mediated cycloaddition of arenes with an N‐N‐arenophile and in situ diimide reduction. Subsequent cycloreversion or fragmentation of the arenophile moiety affords 1,3‐cyclohexadienes or 1,4‐diaminocyclohex‐2‐enes, compounds that are not synthetically accessible using existing dearomatization reactions. Importantly, this strategy also provides numerous opportunities for further derivatization as well as site‐selective functionalization of polynuclear arenes.     

meso‐N‐Pyrrole as a Versatile Substituent Influencing the Optical Properties of Porphyrin

A meso‐N‐pyrrole porphyrin converts into a π‐extended porphyrin forming an indolizine‐3‐one motif. The indolizine‐3‐one frame opens a lactam subunit preserving a six‐membered, heterocyclic structure fused with the main macrocycle. The optical properties of formed derivatives follow the structural modifications giving the absorbance and emission eventually modulated by the NH‐centered modifications of the fused unit.     

Synthesis and Visible Spectral Behaviour of Some New N‐Bridgehead Heterocyclic Cyanine Dyes Incorporating Pyrazolo (4,5‐b) Indolizine (Benzoindolizine)

The new unsymmetrical N‐bridgehead, apo (zeromethine), mono‐methine, dimethine, meso substituted tetramethine and styryl cyanine dyes incorporating pyrazolo (4,5‐b) indolizine (benzoindolizine) nuclei were prepared. Structural confirmation was carried out by elemental analyses, IR, H‐NMR, mass spectra and ¹³C‐NMR with the aid of carbon DEPT spectral data. The visible absorption spectra for the newly synthesized cyanines were examined in 95% ethanol.     

Visible‐Light‐Mediated Generation of Nitrogen‐Centered Radicals: Metal‐Free Hydroimination and Iminohydroxylation Cyclization Reactions

The formation and use of iminyl radicals in novel and divergent hydroimination and iminohydroxylation cyclization reactions has been accomplished through the design of a new class of reactive O‐aryl oximes. Owing to their low reduction potentials, the inexpensive organic dye eosin Y could be used as the photocatalyst of the organocatalytic hydroimination reaction. Furthermore, reaction conditions for a unique iminohydroxylation were identified; visible‐light‐mediated electron transfer from novel electron donor–acceptor complexes of the oximes and Et₃N was proposed as a key step of this process.     

Palladium‐Catalyzed Dearomative syn‐1,4‐Carboamination with Grignard Reagents

A protocol for palladium‐catalyzed dearomative functionalization of simple, nonactivated arenes with Grignard reagents has been established. This one‐pot method features a visible‐light‐mediated [4+2] cycloaddition between an arene and an arenophile, and subsequent palladium‐catalyzed allylic substitution of the resulting cycloadduct with a Grignard reagent. A variety of arenes and Grignard reagents can participate in this process, forming carboaminated products with exclusive syn‐1,4‐selectivity. Moreover, the dearomatized products are amenable to further elaborations, providing functionalized alicyclic motifs and pharmacophores. For example, naphthalene was converted into sertraline, one of the most prescribed antidepressants, in only four operations. Finally, this process could also be conducted in an enantioselective fashion, as demonstrated with the desymmetrization of naphthalene.     

Discovery of Key TIPS‐Naphthalene for Efficient Visible‐to‐UV Photon Upconversion under Sunlight and Room Light**

While many studies have been done on triplet–triplet annihilation‐based photon upconversion (TTA‐UC) to produce visible light with high efficiency, the efficient TTA‐UC from visible to UV light, despite its importance for a variety of solar and indoor applications, remains a challenging task. Here, we report the highest visible‐to‐UV TTA‐UC efficiency of 20.5 % based on the discovery of an excellent UV emitter, 1,4‐bis((triisopropylsilyl)ethynyl)naphthalene (TIPS‐Nph). TIPS‐Nph is an acceptor with desirable features of high fluorescence quantum yield and high singlet generation efficiency by TTA. TIPS‐Nph has a low enough triplet energy level to be sensitized by Ir(C6)₂(acac), a superior donor that does not quench UV emission. The combination of TIPS‐Nph and Ir(C6)₂(acac) realizes the efficient UV light production even with weak light sources such as an AM 1.5 solar simulator and room LEDs.     

Molecular Design Principles for Near‐Infrared Absorbing and Emitting Indolizine Dyes

Desirable components for dye‐sensitzed solar cell (DSC) sensitizers and fluorescent imaging dyes include strong donating building blocks coupled with well‐balanced acceptor functionalities for absorption beyond the visible range. We have evaluated the effects of increasing acceptor strengths and incorporation of dye morphology controlling groups on molar absorptivity and absorption breadth with indolizine donor‐based dyes. Indolizine‐based D –A and D –π–A sensitizers incorporating bis‐rhodanine, tricyanofuran (TCF), and cyanoacrylic acid functionalities were analyzed for performance in DSC devices. The TCF derivatives were also evaluated as near‐infrared (NIR)‐emissive materials with the AH25 emissions extending past 1000 nm.     

Photocontrolled Synthesis of n‐Type Conjugated Polymers

Current approaches to synthesize π‐conjugated polymers (CPs) are dominated by thermally driven, transition‐metal‐mediated reactions. Herein we show that electron‐deficient Grignard monomers readily polymerize under visible‐light irradiation at room temperature in the absence of a catalyst. The product distribution can be tuned by the wavelength of irradiation based on the absorption of the polymer. Conversion studies are consistent with an uncontrolled chain‐growth process; correspondingly, chain extension produces all‐conjugated n‐type block copolymers. Preliminary results demonstrate that the polymerization can be expanded to donor–acceptor alternating copolymers. We anticipate that this method can serve as a platform to access new architectures of n‐type CPs without the need for transition‐metal catalysis.