ChemPhotoChem最新文献

The Front Cover illustrates the micro-environments associated with photocatalytic cross-dehydrogenative coupling (CDC) reactions, wherein covalent organic frameworks (COFs) function as heterogeneous catalysts. COFs exhibit favorable photocatalytic activity in diverse chemical transformations, owing to their remarkable high crystallinity, excellent stability, and convenient recyclability. The CDC reactions represent an efficient and clean methodology for the formation of C-Nu (Nu = nucleophilic reagent) bonds through activation of C-H and Nu-H bonds, respectively. As expected, the robust COFs offer a highly versatile platform for heterogeneous photocatalytic CDC reactions. More information can be found in the Concept article by Bin Guo, David J. Young, Hong-Xi Li, and co-workers (DOI: 10.1002/cptc.202400274).

The Front Cover illustrates organohalogenochromism (OHC) which induces a significant hypsochromic or bathochromic shift of photoabsorption band of dye in halogenated solvents. The expression of OHC would be ascribable to the specific intermolecular interaction between the organohalogen and the dye molecules, including halogen−anion interaction (i.e. halogen bond) and halogen/π interaction. The insight into the OHC allows us to create an optical spectroscopic method and functional dye material for detection and visualization of toxic volatile organohalogen compounds. More information can be found in the Concept article by Yousuke Ooyama and co-workers (DOI: 10.1002/cptc.202400187).

The Front Cover illustrates the improvement on stability as well as on thermally activated delayed fluorescence (TADF) characteristics, such as lifetime and efficiency, obtained by modifying the core of the organic emitters. The properties of TADF dyes are enhanced going from 9,9-dimethyl-fluorene to the more bulky 9,9’-spirobifluorene. Very long delayed fluorescence has been detected in both dyes as thin films and crystals, where the bulky core is pivotal to reduce deactivating intermolecular pathways. More information can be found in the Research Article by Fabio Rizzo and co-workers (DOI: 10.1002/cptc.202400235).

The amyloidogenic homotetrameric plasma protein transthyretin (TTR) has an affinity for bicyclic small molecule ligands in its two thyroxine (T4) binding sites. We have shown that native tetrameric TTR binds to amyloid ligands based on the trans-stilbene scaffold. The fluorescent Congo-red analogue, X34, is a symmetric bi-trans-stilbene that contains two salicylic acid motifs. We used fluorescence spectroscopy methods to interrogate X34 binding to the TTR tetramer and fibril. We discovered two binding sites in both TTR forms by tryptophan FRET, ligand self-quenching, Stern-Volmer plots and binding curves, for the latter including the competitive ligand diflunisal. X34 binds with the similar affinity as diflunisal in the first binding site (K_d1=150 nM), and negative cooperativity renders the binding to the second site with lower affinity very similar compared to diflunisal (K_d2= 1.1 μM). This behavior is coherent with the salicylic acid moiety of diflunisal binding into the binding pocket of TTR (reverse mode). Interestingly X34 binding to TTR fibrils was also well fitted to two binding sites, however with overall lower affinity (K_d1=1.2 μM; K_d2=2.1 μM) compared to binding to the native tetramer. X34 fluorescence when bound to TTR-fibrils was significantly blue shifted compared to binding to the TTR-tetramer.

The photophysical and two-photon absorption (TPA) properties of five push-pull pyrimidine derivatives were studied upon protonation with trifluoroacetic acid (TFA). The pyrimidine heterocycles have been used as the protonation sites and electron acceptors while methoxy groups were employed as electron donors. Steady state and fluorescence time-resolved spectroscopy from femtoseconds to nanoseconds have been used together with the two-photon excited fluorescence method. Protonation with TFA resulted in red-shifted absorption and fluorescence spectra as well as to an acceleration of the excited state dynamics. The TPA properties showed a remarkable enhancement upon protonation with a ten-times increase of the TPA cross sections due to an increased intramolecular charge transfer. Our results demonstrate the potential of pyrimidine chromophores to be used as protonation tunable non-linear optical chromophores.

A fluorenone derivative with an extended conjugated structure emitting visible light was examined as a functional fluorescent dye that responds to solvent and heat stimuli in a precisely controlled manner. Intermolecular hydrogen bonds between the fluorenone dye and solvent, which cause fluorescence (FL) quenching due to vibronic coupling, were broken and regenerated by adjusting the hydrogen bond acidity and basicity of solvent mixtures in various combinations or by varying the temperature. The fluorenone dye exhibited a unique heat-induced FL emission enhancement during heating and returned to the quenched state during cooling. Thus, this FL change was highly reversible and repeatable. Moreover, through thermodynamic consideration based on the spectroscopic analysis, the Gibbs energy change was calculated for each solvent mixture composition to predict the thermodynamic preference for FL enhancement.

The research focuses on the innovative use of graphite-like carbon nitride (gC₃N₄) catalysts along with supercritical carbon dioxide (scCO₂) for the green synthesis of valuable organic compounds. Having explored different synthetic routes for gC₃N₄ and the obtained samples efficiency in the photocatalytic oxidation of benzyl alcohol with molecular oxygen in scCO₂, we identified the most effective catalyst bearing ether linkers between layers of a graphite-like structure. This catalyst facilitates the production of benzaldehyde and benzoic acid derivatives, highlighting the potential for sustainable industrial applications. The study's emphasis on a metal-free catalyst and a zero-waste process underlines its contribution to environmentally friendly chemical practices. The proposed approach offers a more sustainable and efficient alternative to traditional processes in small-scale chemical production.

Herein, we report extended π-conjugated arylazopyrazole and arylazoisoxazole photoswitches towards tuning and modulation of their intrinsic properties. In this regard, we systematically introduced phenyl, styryl, (triphenylvinyl)styryl, phenylethynyl groups at ortho, meta, and para positions relative to the azo unit to extend the π-conjugation and vary the electronic coupling. In addition, the heterocyclic substituents were also modified. Overall, 20 photoswitches with modular substituents have been synthesized and studied for the photoswitching ability and thermal relaxations of Z isomers in the solution phase and solid state. Besides deciphering the importance of extending conjugation in photoswitching characteristics, intriguing properties such as mechanochromism and reversible bidirectional photochromism in the solid state were also unravelled. Through extensive spectroscopic studies, we envisage the effect of electronic coupling due to π-conjugation and its impact on longer wavelength light-induced photoswitching that holds several application potentials.

The Front Cover highlights investigations of the reactivity of Cannabigerol (CBG) in organic solvents under both photochemical and acid catalyzed conditions, pointing out the key role of the photoexcited CBG* in the selective formation of a 2,2-disubstituted-chromane derivative (green path). On the other hand, in the presence of Brønsted-Lowry acids, two tertiary carbocations are competitively generated (I⁺, II⁺, orange and blue paths). Finally, when performing the reaction in toluene in the presence of BF₃*OEt₂, a Friedel Crafts-like alkylation of the solvent was noticed (purple paths). More information can be found in the Research Article by Daniele Merli, Stefano Protti, and co-workers (DOI: 10.1002/cptc.202400157).

Photocatalytic technology has shown great potential in various fields such as environmental purification, energy conversion, and chemical transformations due to its green, sustainable, and low-cost characteristics. Porous aromatic frameworks (PAFs) with high specific surface areas, designable local structures, and abundant active sites could potentially serve as efficient photocatalysts for various catalytic reactions. This makes PAFs have a wide range of application prospects and significant advantages in the field of photocatalysis. This concept discusses the recent progress of photocatalysis over PAFs. Various strategies are used to solve the general problems of photocatalyst, such as poor light absorption, low carrier separation efficiency and poor stability, which further reveal the relationship between their structures and performances.