ChemPhotoChem最新文献

We present a novel method for synthesizing water-based non-conjugated polymer nanoparticles that possess green fluorescence. This synthesis involves the crosslinking of polyethyleneimine (PEI) with glutaraldehyde (GA), followed by in situ polymerization of an acrylic acid-based monomer. The nanoparticles are formed through self-assembly driven by in situ electrostatic complexation, resulting in unique photoluminescence properties. This process involves the negatively charged polymer, formed via graft and homo-polymerization, interacting with the pre-existing positively charged PEI. The nanoparticles consist solely of heteroatomic bonds like C−O, C−N, C=O, and C=N. The restriction of vibrational and rotational relaxation of these bonds within the nanoscale poly-ionic complex enhances their photoluminescence properties. For example, glutaraldehyde-crosslinked polyethyleneimine/poly(methacrylic acid) (gPEI/PMAA) nanoparticles produced by this method demonstrate outstanding properties including a narrow size distribution with an average diameter of 35 nm, excitation-dependent fluorescence with a green emission peak at 527 nm when excited at 480 nm, and a high quantum yield of up to 23.6 % (±1.2 %). The green fluorescence property of the nanoparticles can be used in the generation of white LED light through incorporating them with silicone and coating them onto a blue light LED chip. This study represents a significant improvement in the fluorescence properties of PEI-based materials and opens up new possibilities for their applications in various fields.

A significant hypsochromic or bathochromic shift of photoabsorption bands of dyes may be observed only in halogenated solvents. Such specific solvatochromism is termed organohalogenochromism (OHC), which has been recently recognized as a photophysical phenomenon. However, few studies have been carried out on the elucidation of OHC and thus there is a limited insight into the mechanism for expression of OHC, although the phenomenon not only is of a great scientific interest in photochemistry, photophysics, analytical chemistry, and synthetic organic chemistry but also has great potential for development of colorimetric detection technique for organohalogen compounds; this technique is expected to be facile operation and simple analysis with sufficient accuracy, high sensitivity, and fast response, and thus allows visualization and real-time monitoring for toxic volatile organohalogen compounds (VOHCs). In this Concept, we first review OHC of dyes which have been reported so far. Second, the elucidation of OHC based on the interactions between dye and organohalogen molecules are discussed. In particular, we propose the explanation for a pronounced OHC of donor-π-acceptor-type cationic dye from the viewpoint of halogen bond (XB) between halogenated solvents and counter anion of cationic dye. Moreover, an application of organohalogenochromic dyes to colorimetric sensors for VOHCs is presented.

Covalent organic frameworks (COFs) are robust, porous materials with well-defined structures that have been employed for gas separation, photoluminescence, sensing, energy storage, and heterogeneous catalysis. This review summarizes recent progress in the use of COFs as a versatile platform for heterogeneous photocatalytic cross-dehydrogenative coupling (CDC) reactions, which are an efficient and clean methodology for the formation of C−C or C−P bonds. We review the synthesis of these photocatalytic COFs, correlating their catalytic performance with their structures and photoelectric properties.

The development of a stable, non-toxic material that emits electrons following absorption of visible light may have a major impact on the solar photocatalysis of difficult reactions such as CO₂ and N₂ reduction, as well as for targeted chemical transformations in general. Diamond is a good candidate, however it is a wide bandgap material requiring deep UV photons ($$<227 nm) to promote electrons from the valence band into the conduction band. Embedding silver nanoparticles under the diamond surface allows the photoconductivity of the diamond in the spectral region of the surface plasmon resonance to be increased, while also leading to an enhancement of visible light photoemission. Considering the low intensity of the light sources used in this work and the spectral properties of the enhanced photoconductivity and photoemission a mechanism based on plasmonically enhanced photoconductivity which in turn allows surface states emptied by photoemission to be recharged thus leading to enhanced photoemission in the visible range is proposed.

Triaminoguanidinium (TG)-based C₃-symmetric-like molecular architectures with diverse donors and acceptors are well established as organic molecular materials for promising stimuli-responsive and metal sensing-based applications. However, the mechanofluorochromic (MFC) response was unremarkable upon applying external mechanical stress. Even though some show MFC features, there was no optical shift under ambient light. In this paper, we developed a novel C₃-symmetric molecule, TAC₃, containing the TG core linked with conformationally twisted thiophene-linked anthracenyl terminals. Three conformationally deformed hands in TAC₃ respond against external mechanical stimuli with a redshifted absorption and emission, easily detectable through the naked eye. Although MFC features were reported before for such C₃-symmetric molecules, the change in absorbance was not identified. In addition, TAC₃ could selectively detect Pd²⁺ through extreme emission quenching (green to black). The mechanochromism and sensing outcomes are elucidated by the experimental and theoretical support. Compared to the previous reports, the notable 2 : 3 (metal: ligand) binding due to geometric restriction creating a specific pocket size for Pd⁺² is unusual for this system. The onsite application on Pd²⁺ detection and measurable MFC features are demonstrated to validate the potential of this C₃-symmetric molecule in advanced optoelectronic applications such as security writing and Pd²⁺ ion detection.

Direct functionalization of C−H bonds is the most expeditious strategy to build complexity into organic molecules. Unfortunately, most Pd-catalyzed C−H arylation strategies require high temperatures and/or stoichiometric oxidants. The discovery of metallaphotoredox C−H arylation in 2011 forged a new approach to achieve metal catalyzed C−H arylation at room temperature. Since this discovery, most reports still use explosive diazonium salts as aryl radical precursors. Alternatively, a single report uses bench-stable diaryliodonium salts, albeit with an Ir-based photocatalyst. In this study, we develop an organophotoredox manifold that enables Pd-catalyzed C−H arylation of numerous N-aryl amide substrates. The results we present are expected to revitalize the use of diaryliodonium salts to achieve room temperature arylations of wide-ranging classes of C−H bonds.

Organic room-temperature phosphorescent (RTP) materials have garnered significant attention owing to their unique photophysical properties. Traditionally, the stabilization of triplet excitons in RTP materials necessitates a crystalline matrix or rigid polymer chain, which limits their use in flexible materials. In contrast, hydrogels offer biocompatibility, softness, and ease of processing. Therefore, incorporating phosphorescent molecules into hydrogel systems can expand the application potential of RTP materials. This concept summarizes recent advancements in RTP hydrogels, emphasizing their synthetic strategies and diverse applications.

Electron-rich symmetric pull-push-pull molecules can act as efficient two-photon absorbing units. When these chromophores are bonded directly to photo-switchable molecules they can function as antenna systems to indirectly induce photochemical transformations in isomerizable groups after energy transfer. Recently, we developed an antenna–molecular switch system based on a pyrrolo–pyrrole two-photon active chromophore. When this antenna section is functionalized with symmetrically situated azo-sections as N,N’-pyrrolic-substituents, these azo molecular switches can be efficiently transformed from their E to their Z isomers after non-linear light absorption by the antenna, followed by indirect excitation of the azo-sections. In this contribution we present a case-study of one of these systems through femtosecond-resolved fluorescence to observe the dynamics involved in the excitation and relaxation steps within the antenna section, as well as the energy transfer pathways. By time-resolving the emission signals we observed that the energy transfer can occur in parallel with the relaxation within the first singlet vibronic states localized at the pyrrolo–pyrrole antenna. In fact, the antenna-to-azo section energy transfer shows a biphasic nature. At early times, during the relaxation within the antenna, there is an initial population of azo-section excited molecules. In addition, after the system has evolved to the fully relaxed S₁ state at the antenna section, the energy transfer has components related to thermal fluctuations which increase the couplings with the receiver states at the azo-switches giving transfer rates of the order of 10¹⁰ s⁻¹ at room temperature. The characterization of these relaxation and energy transfer steps, as well as the role of the solvent in these processes, gives insights for the development of future molecules with indirect two-photon isomerization properties using this kind of pull-push-pull two-photon active antenna. Due to their two-photon reactive properties, these systems can have applications in schemes where highly localized photo-isomerization is required.

In the pursuit of efficient and cost-effective organic light-emitting diodes (OLEDs), the development of solution-processed hybridized local and charge transfer (HLCT) emitters presents a promising approach. HLCT materials uniquely integrate the advantages of both singlet and triplet excitons, surpassing the traditional spin statistical limit of 25 % while offering high photoluminescence efficiency and balanced charge transport properties. Herein, we report the synthesis and characterization of two new deep blue, solution-processable HLCT fluorophores, G1FTPI and G2FTPI. These compounds incorporate fluorenyl carbazole dendron units into the HLCT luminogenic triphenylamine-phenanthroimidazole (TPI) molecule. Their HLCT and photoluminescence (PL) properties were experimentally and theoretically investigated using solvation effects and density functional theory (DFT) calculations. The molecules exhibit deep blue emission with a high solid-state fluorescence quantum yield, good solution-processed film-forming quality, and high hole mobility values of 2.18–2.61×10⁻⁶ cm² V⁻¹ s⁻¹. Both compounds were successfully employed as non-doped emissive layers in solution-processed OLEDs, demonstrating excellent electroluminescent (EL) performance. Notably, the G2FTPI-based device emitted a deep blue light at 432 nm with CIE coordinates of (0.158, 0.098) and achieved a maximum current efficiency (CE_max) of 3.13 cd A⁻¹ and a maximum external quantum efficiency (EQE_max) of 5.30 %.

Cyanofunctionalization of alkenes via radical-initiated cyano migration was a straightforward pathway to access alkyl nitriles. Herein, By the synergistic merger of photoredox catalysis and Brønsted base catalysis, a mild protocol of alkylcyanation of unactivated alkenes with protic C(sp³)−H feedstocks via intramolecular 1,4-cyano group migration was reported. This method was enabled in an atom-, and step-economy manner, delivering a series of γ-cyanoester derivatives in moderate to excellent yields.