Tetraacylgermanes: Highly Efficient Photoinitiators for Visible‐Light‐Induced Free‐Radical Polymerization

In this contribution a convenient synthetic method to obtain tetraacylgermanes Ge[C(O)R]₄ (R=mesityl ( 1 a ), phenyl ( 1 b )), a previously unknown class of highly efficient Ge‐based photoinitiators, is described. Tetraacylgermanes are easily accessible via a one‐pot synthetic protocol in >85 % yield, as confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. The efficiency of 1 a , b as photoinitiators is demonstrated in photobleaching (UV/Vis), time‐resolved EPR (CIDEP), and NMR/CIDNP investigations as well as by photo‐DSC studies. Remarkably, the tetraacylgermanes exceed the performance of currently known long‐wavelength visible‐light photoinitiators for free‐radical polymerization     

A Multicolor Photoinitiator for Cationic Polymerization and Interpenetrated Polymer Network Synthesis: 2,7‐Di‐tert‐butyldimethyldihydropyrene

For polymer synthesis upon visible light, actual photoinitiator operates in a restricted part of the spectrum. As a consequence, several photoinitiators are necessary to harvest all of the emitted visible photons. Herein, 2,7‐di‐tert‐butyldimethyldihydropyrene is used for the first time as a multicolor photoinitiator for the cationic polymerization of epoxides. Upon addition of diphenyliodonium hexafluorophosphate and optionally N‐vinylcarbazole, the originality of this approach is to allow efficient monomer conversions under various excitation light sources in the 360–650 nm wavelength range: halogen lamps, and light‐emitting and laser diodes. The synthesis of an interpenetrated polymer network from an epoxide/acrylate blend using a red light at 635 nm is also feasible. The formed polymer material exhibits a photochromic character.

     

Carbon Dots as a Promising Green Photocatalyst for Free Radical and ATRP‐Based Radical Photopolymerization with Blue LEDs

Carbon dots (CDs) have been used for the first time as a sensitizer to initiate and activate free radical and controlled radical polymerization, respectively, based on an ATRP protocol with blue LEDs. Consideration of diverse heteroatom‐doped CDs indicated that N‐doped CDs could serve as an effective photocatalyst and photosensitizer in combination with LEDs emitting either at 405 nm or 470 nm. Free radical polymerization was initiated by combining the CDs with an iodonium or sulfonium salt in tri(propylene glycol) diacrylate. Polymerization of methyl methacrylate (MMA) by photo‐induced ATRP was achieved with CDs and ethyl α‐bromophenylacetate using Cu^II as catalyst in the ppm range. The polymers obtained showed temporal control, narrower dispersity ?1.5, and chain‐end fidelity. The first‐order kinetics and ON/OFF experiments additionally gave evidence of the constant concentration of polymer radicals. No remarkable cytotoxic activity was observed for the CDs, underlining their biocompatibility.     

Near‐Infrared Phosphorus‐Substituted Rhodamine with Emission Wavelength above 700 nm for Bioimaging

Phosphorus has been successfully fused into a classic rhodamine framework, in which it replaces the bridging oxygen atom to give a series of phosphorus‐substituted rhodamines (PRs). Because of the electron‐accepting properties of the phosphorus moiety, which is due to effective σ*–π* interactions and strengthened by the inductivity of phosphine oxide, PR exhibits extraordinary long‐wavelength fluorescence emission, elongating to the region above 700 nm, with bathochromic shifts of 140 and 40 nm relative to rhodamine and silicon‐substituted rhodamine, respectively. Other advantageous properties of the rhodamine family, including high molar extinction coefficient, considerable quantum efficiency, high water solubility, pH‐independent emission, great tolerance to photobleaching, and low cytotoxicity, stay intact in PR. Given these excellent properties, PR is desirable for NIR‐fluorescence imaging in vivo.     

Highly Selective Photoreduction of CO2 with Suppressing H2 Evolution over Monolayer Layered Double Hydroxide under Irradiation above 600 nm

Although progress has been made to improve photocatalytic CO₂ reduction under visible light (λ>400 nm), the development of photocatalysts that can work under a longer wavelength (λ>600 nm) remains a challenge. Now, a heterogeneous photocatalyst system consisting of a ruthenium complex and a monolayer nickel‐alumina layered double hydroxide (NiAl‐LDH), which act as light‐harvesting and catalytic units for selective photoreduction of CO₂ and H₂O into CH₄ and CO under irradiation with λ>400 nm. By precisely tuning the irradiation wavelength, the selectivity of CH₄ can be improved to 70.3 %, and the H₂ evolution reaction can be completely suppressed under irradiation with λ>600 nm. The photogenerated electrons matching the energy levels of photosensitizer and m‐NiAl‐LDH only localized at the defect state, providing a driving force of 0.313 eV to overcome the Gibbs free energy barrier of CO₂ reduction to CH₄ (0.127 eV), rather than that for H₂ evolution (0.425 eV).     

Visible‐Light/Photoredox‐Mediated sp3 CH Functionalization and Coupling of Secondary Amines with Vinyl Azides in Flow Microreactors

Structurally diverse imidazole derivatives were synthesized by a visible‐light/[Ru(bpy)₃][(PF₆)₂]‐mediated coupling of vinyl azides and secondary amines in flow microreactors. This operationally simple and atom‐economical protocol allows the formation of three new C?N bonds through the functionalization of sp³ C?H bonds adjacent to the secondary nitrogen atom. In order to get mechanistic insight of the coupling reaction, several control experiments were carried out and discussed.     

A Complex Perovskite‐Type Oxynitride: The First Photocatalyst for Water Splitting Operable at up to 600 nm

One of the simplest methods for splitting water into H₂ and O₂ with solar energy entails the use of a particulate‐type semiconductor photocatalyst. To harness solar energy efficiently, a new water‐splitting photocatalyst that is active over a wider range of the visible spectrum has been developed. In particular, a complex perovskite‐type oxynitride, LaMg_xTa_1?xO_1+3xN_2?3x (x≥1/3), can be employed for overall water splitting at wavelengths of up to 600 nm. Two effective strategies for overall water splitting were developed. The first entails the compositional fine‐tuning of a photocatalyst to adjust the bandgap energy and position by forming a series of LaMg_xTa_1?xO_1+3xN_2?3x solid solutions. The second method is based on the surface coating of the photocatalyst with a layer of amorphous oxyhydroxide to control the surface redox reactions. By combining these two strategies, the degradation of the photocatalyst and the reverse reaction could be prevented, resulting in successful overall water splitting.     

Fabrication of Mesoporous‐Silica‐Coated Upconverting Nanoparticles with Ultrafast Photosensitizer Loading and 808 nm NIR‐Light‐Triggering Capability for Photodynamic Therapy

A novel photodynamic therapy nanoplatform based on mesoporous‐silica‐coated upconverting nanoparticles (UCNP) with electrostatic‐driven ultrafast photosensitizer (PS) loading and 808 nm near infrared (NIR)‐light‐triggering capabilities has been fabricated. By positively charging inner channels of the mesoporous silica shell with amino groups, a quantitative dosage of negatively charged PS, exemplified with Rose Bengal (RB) molecules, can be loaded in 2 min. In addition, the electrostatic‐driven technique simultaneously provides the platform with both excellent PS dispersity and leak‐proof properties due to the repulsion between the same‐charged molecules and the electrostatic attraction between different‐charged PS and silica channel walls, respectively. The as‐coated silica shell with an ultrathin thickness of 12±2 nm is delicately fabricated to facilitate ultrafast PS loading and efficient energy transfer from UCNP to PS. The outside surface of the silica shell is capped with hydrophilic β‐cyclodextrin, which not only enhances the dispersion of resulting nanoparticles in water but also plays a role of “gatekeeper”, blocking the pore opening and preventing PS leaking. The in vitro cellular lethality experiment demonstrates that RB molecules can be activated to effectively generate singlet oxygen and kill cancer cells upon 808 nm NIR light irradiation.     

Saccharin‐Based μ‐Oxo Imidoiodane: A Readily Available and Highly Reactive Reagent for Electrophilic Amination

Three new saccharin‐based hypervalent iodine compounds were prepared by the reaction of saccharine with (diacetoxyiodo)arenes or acetoxybenziodoxole. Structures of these new imidoiodanes were established by X‐ray crystallography. The saccharin‐based μ‐oxo‐bridged imidoiodane readily reacts with silyl enol ethers under mild conditions to give the corresponding α‐aminated carbonyl compounds in moderate yields.     

Elucidating Molecule–Plasmon Interactions in Nanocavities with 2 nm Spatial Resolution and at the Single‐Molecule Level

The fundamental understanding of the subtle interactions between molecules and plasmons is of great significance for the development of plasmon‐enhanced spectroscopy (PES) techniques with ultrahigh sensitivity. However, this information has been elusive due to the complex mechanisms and difficulty in reliably constructing and precisely controlling interactions in well‐defined plasmonic systems. Herein, the interactions in plasmonic nanocavities of film‐coupled metallic nanocubes (NCs) are investigated. Through engineering the spacer layer, molecule–plasmon interactions were precisely controlled and resolved within 2 nm. Efficient energy exchange interactions between the NCs and the surface within the 1–2 nm range are demonstrated. Additionally, optical dressed molecular excited states with a huge Lamb shift of ≈7 meV at the single‐molecule (SM) level were observed. This work provides a basis for understanding the underlying molecule–plasmon interaction, paving the way for fully manipulating light–matter interactions at the nanoscale.     

Indachlorins: Nonplanar Indanone‐Annulated Chlorin Analogues with Panchromatic Absorption Spectra between 300 and 900 nm

Indaphyrins, pyrrole‐modified porphyrins containing a cleaved pyrrole β,β′‐bond and two annulated indanone moieties, possess unusually broadened and redshifted UV/Vis spectra because of their π‐expanded chromophores. The parent free base indaphyrin has been crystallographically characterized, highlighting its strongly ruffled conformation incorporating a helimeric twist. It was shown to be susceptible to regiospecific derivatizations at the opposite side of the ring‐cleaved pyrrole (dihydroxylation, followed by functional group transformations of the resulting diol functionality), generating indaphyrin‐based chlorin analogues, indachlorins, that incorporate a dihydroxypyrroline, pyrrolindione, oxazolone, or a morpholine moiety. Structural modifications resulted in further broadening and hyper‐ and bathochromic shifts of the optical spectra, some of which possess a nearly panchromatic absorption between 300 to well above 900 nm. The extents to which these modifications affect their solid‐state conformations were analyzed.     

Highly Conductive PEDOT:PSS Films with 1,3‐Dimethyl‐2‐Imidazolidinone as Transparent Electrodes for Organic Light‐Emitting Diodes

Highly conductive poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as transparent electrodes for organic light‐emitting diodes (OLEDs) are doped with a new solvent 1,3‐dimethyl‐2‐imidazolidinone (DMI) and are optimized using solvent post‐treatment. The DMI doped PEDOT:PSS films show significantly enhanced conductivities up to 812.1 S cm⁻¹. The sheet resistance of the PEDOT:PSS films doped with DMI is further reduced by various solvent post‐treatment. The effect of solvent post‐treatment on DMI doped PEDOT:PSS films is investigated and is shown to reduce insulating PSS in the conductive films. The solvent posttreated PEDOT:PSS films are successfully employed as transparent electrodes in white OLEDs. It is shown that the efficiency of OLEDs with the optimized DMI doped PEDOT:PSS films is higher than that of reference OLEDs doped with a conventional solvent (ethylene glycol). The results present that the optimized PEDOT:PSS films with the new solvent of DMI can be a promising transparent electrode for low‐cost, efficient ITO‐free white OLEDs.