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Complete experimental section; copies of 1H and 13C NMR spectra for all new compounds; copies of the absorption (UV–vis) and excitation/emission spectra of complexes 3–6; decay curves and fitting data for the determination of the half-life time of complexes 3–6; Cartesian coordinates of all new optimized complexes 3–6 in the ground state using the wB97XD and M06-2X functionals; Cartesian coordinates of S1 optimized geometries using the wB97XD and M06-2X functionals; tables of calculated orbital energies (Hartree) and metal participation, along with the HOMO–LUMO gap (eV) using the wB97XD and M06-2X functionals for the ground state of 3–6; tables with the calculated vertical transitions for the lowest T1, T2, T3, S1, and S2 excited states of 3–6 with the wB97XD and M06-2X functionals; tables with the calculated emission properties from the S1 optimized geometry for the lowest T1, T2, T3, S1, and S2 excited states of 3–6 with the wB97XD and M06-2X functionals; crystallographic tables of compounds 1a, 1e, 3c, 3d, 3g and 7h; and discussion of the structures of compounds 1a, 1e, 3c, 3d, 3g, and 7h.

The synthesis, photophysical properties, and applications of highly fluorescent and phosphorescent palladium complexes are reviewed, covering the period 2018-2022. Despite the fact that the Pd atom appears closely related with an efficient quenching of the fluorescence of different molecules, different synthetic strategies have been recently optimized to achieve the preservation and even the amplification of the luminescent properties of several fluorophores after Pd incorporation. Beyond classical methodologies such as orthopalladation or the use of highly emissive ligands as porphyrins and related systems (for instance, biladiene), new concepts such as AIE (Aggregation Induced Emission) in metallacages or in coordination-driven supramolecular compounds (CDS) by restriction of intramolecular motions (RIM), or complexes showing TADF (Thermally Activated Delayed Fluorescence), are here described and analysed. Without pretending to be comprehensive, selected examples of applications in areas such as the fabrication of lighting devices, biological markers, photodynamic therapy, or oxygen sensing are also here reported.

The development of catalytic systems with different chemo- and biocatalytic functionalities for sustainable one-pot multistep transformations represents a big challenge in modern chemistry. Here, we have designed and synthesized enzyme-metal hybrids’ materials of palladium and copper as multiactive heterogeneous catalysts. The in situ formation of metallic nanoparticles of different size and species on multilayer graphene-anchored Candida antarctica lipase (G@CALB) at room temperature and aqueous media allowed creation of different kinds of enzyme-metal nanoarchitectures, where the metal nanoparticles were synthesized exclusively when induced by an enzyme, dispersed homogeneously on the enzyme structure as the scaffold. The creation of copper or palladium nanoparticles on the graphene-enzyme preparation allowed obtaining a new type of enzyme-metal bifunctional catalyst conserving the enzymatic activity intact and enhancing the metallic properties. Furthermore, the creation of a CuPd alloy on immobilized enzyme preparation (G@CALB-PdNPs-CuNPs) allowed obtaining a new enzyme-bimetallic trifunctional catalyst, with extremely enhanced metallic activity by the synergistic effect. These hybrids were successfully applied in different cascade processes, where the hybrid G@CALB-PdNPs-CuNPs, based on its property, showed superior efficiency to bifunctional hybrids in the regioselective and asymmetric one-pot tandem processes tested.

The irradiation of 2-aryl-4-(E-3′-aryl-allylidene)-5(4H)-oxazolones 1 with blue light (456 nm) in the presence of [Ru(bpy)3](BF4)2 (bpy = 2,2′-bipyridine, 5% mol) gives the unstable cyclobutane-bis(oxazolones) 2 by [2+2]-photocycloaddition of two oxazolones 1. Each oxazolone contributes to the formation of 2 with a different C=C bond, one of them reacting through the exocyclic C=C bond, while the other does so through the styryl group. Treatment of unstable cyclobutanes 2 with NaOMe/MeOH produces the oxazolone ring opening reaction, affording stable styryl-cyclobutane bis(amino acids) 3. The reaction starts with formation of the T1 excited state of the photosensitizer 3[Ru*(bpy)3]2+, which reacts with S0 of oxazolones 1 through energy transfer to give the oxazolone T1 state 3(oxa*)-1, which is the reactive species and was characterized by transient absorption spectroscopy. Measurement of the half-life of 3(oxa*)-1 for 1a, 1b and 1d shows large values for 1a and 1b (10–12 μs), while that of 1d is shorter (726 ns). Density functional theory (DFT) modeling displays strong structural differences in the T1 states of the three oxazolones. Moreover, study of the spin density of T1 state 3(oxa*)-1 provides clues to understanding the different reactivity of 4-allylidene-oxazolones described here with respect to the previously reported 4-arylidene-oxazolones.

The present work sheds light on a generally overlooked issue in the emerging field of bio-orthogonal catalysis within tumour microenvironments (TMEs): the interplay between homogeneous and heterogeneous catalytic processes. In most cases, previous works dealing with nanoparticle-based catalysis in the TME focus on the effects obtained (e.g. tumour cell death) and attribute the results to heterogeneous processes alone. The specific mechanisms are rarely substantiated and, furthermore, the possibility of a significant contribution of homogeneous processes by leached species – and the complexes that they may form with biomolecules – is neither contemplated nor pursued. Herein, we have designed a bimetallic catalyst nanoparticle containing Cu and Fe species and we have been able to describe the whole picture in a more complex scenario where both homogeneous and heterogeneous processes are coupled and fostered under TME relevant chemical conditions. We investigate the preferential leaching of Cu ions in the presence of a TME overexpressed biomolecule such as glutathione (GSH). We demonstrate that these homogeneous processes initiated by the released by Cu–GSH interactions are in fact responsible for the greater part of the cell death effects found (GSH, a scavenger of reactive oxygen species, is depleted and highly active superoxide anions are generated in the same catalytic cycle). The remaining solid CuFe nanoparticle becomes an active catalyst to supply oxygen from oxygen reduced species, such as superoxide anions (by-product from GSH oxidation) and hydrogen peroxide, another species that is enriched in the TME. This activity is essential to sustain the homogeneous catalytic cycle in the oxygen-deprived tumour microenvironment. The combined heterogeneous–homogeneous mechanisms revealed themselves as highly efficient in selectively killing cancer cells, due to their higher GSH levels compared to healthy cell lines.

Given the potential applications of fluorescent carbon nanoparticles in biomedicine, the relationship between their chemical structure, optical properties and biocompatibility has to be investigated in detail. In this work, different types of fluorescent carbon nanoparticles are synthesized by acid treatment, sonochemical treatment, electrochemical cleavage and polycondensation. The particle size ranges from 1 to 6 nm, depending on the synthesis method. Nanoparticles that were prepared by acid or sonochemical treatments from graphite keep a crystalline core and can be classified as graphene quantum dots. The electrochemically produced nanoparticles do not clearly show the graphene core, but it is made of heterogeneous aromatic structures with limited size. The polycondensation nanoparticles do not have C=C double bonds. The type of functional groups on the carbon backbone and the optical properties, both absorbance and photoluminescence, strongly depend on the nanoparticle origin. The selected types of nanoparticles are compatible with human intestinal cells, while three of them also show activity against colon cancer cells. The widely different properties of the nanoparticle types need to be considered for their use as diagnosis markers and therapeutic vehicles, specifically in the digestive system.

We present a general procedure for the synthesis and in situ functionalization of highly fluorescent non-conjugated polymer dots, by exploiting the room-temperature carbodiimide-mediated condensation between citric acid and amines. The versatility of this method is proved by the preparation and characterization of a broad set of fluorescent nanoparticles with customized polymer structures and functional groups.

Transition-metal dichalcogenides (TMDs) attract increased attention for the development of donor–acceptor materials enabling improved light harvesting and optoelectronic applications. The development of novel donor–acceptor nanoensembles consisting of poly(3-thiophene sodium acetate) and ammonium functionalized MoS2 and WS2 was accomplished, while photoelectrochemical cells were fabricated and examined. Attractive interactions between the negatively charged carboxylate anion on the polythiophene backbone and the positively charged ammonium moieties on the TMDs enabled in a controlled way and in aqueous dispersions the electrostatic association of two species, evidenced upon titration experiments. A progressive quenching of the characteristic fluorescence emission of the polythiophene derivative at 555 nm revealed photoinduced intraensemble energy and/or electron transfer from the polymer to the conduction band of the two TMDs. Photoelectrochemical assays further confirmed the establishment of photoinduced charge-transfer processes in thin films, with distinct responses for the MoS2- and WS2-based systems. The MoS2-based ensemble exhibited enhanced photoanodic currents offering additional channels for hole transfer to the solution, whereas the WS2-based one displayed increased photocathodic currents providing supplementary pathways of electron transfer to the solution. Moreover, scan direction depending on photoanodic and photocathodic currents suggested the existence of yet unexploited photoinduced memory effects. These findings highlight the value of electrostatic interactions for the creation of novel donor–acceptor TMD-based ensembles and their relevance for managing the performance of photoelectrochemical and optoelectronic processes.

Photochemical processes are experiencing a renewed interest, because they exploit alternative reaction pathways through electronic excited states, providing access to routes not reachable through the ground state. These processes are usually promoted by visible light and show a high atom economy. In this communication we present methods for the general synthesis of tetrahydroisoquinolone (THIQs) and dihydroisoquinolonecarboxylates (DHIQs), and dihydroquinolones (DHQs) through an intramolecular photochemical cyclization of N-benzoyl-dehydrophenylalanines (see Scheme). The reaction is promoted by Lewis Acids (BF3) and the orientation of the reaction is tuned by changing the substituents R2 and R3. Despite similar photochemical processes appear in the bibliography, the results here reported are totally unprecedented. The reactions show interest because: (i) they provide products with remarkable pharmacological activity; (ii) they occur under mild conditions, in contrast to the harsh conditions often found on classical methods; (iii) they show complete atom-economy and broad scope, tolerating different groups at R1, R2 and R3 positions.

Different Pd-complexes containing orthometallated push–pull oxazolones were inserted by supramolecular Pd-amino acid coordination on two genetically engineered modified variants of the thermoalkalophilic Geobacillus thermocatenolatus lipase (GTL). Pd-lipase conjugation was performed on the solid phase in the previously immobilized form of GTL under mild conditions, and soluble conjugated Pd-GTL complexes were obtained by simply desorbing by washing with an acetonitrile aqueous solution. Three different Pd complexes were incorporated into two different genetically modified enzyme variants, one containing all the natural cysteine residues changed to serine residues, and another variant including an additional Cys mutation directly in the catalytic serine (Ser114Cys). The new Pd–enzyme conjugates were fluorescent even at ppm concentrations, while under the same conditions free Pd complexes did not show fluorescence at all. The Pd conjugation with the enzyme extremely increases the catalytic profile of the corresponding Pd complex from 200 to almost 1000-fold in the hydrogenation of arenes in aqueous media, achieving in the case of GTL conjugated with orthopalladated 4a an outstanding TOF value of 27 428 min−1. Also the applicability of GTL-C114 conjugated with orthopalladated 4b in a site-selective C–H activation reaction under mild conditions has been demonstrated. Therefore, the Pd incorporation into the enzyme produces a highly stable conjugate, and improves remarkably the catalytic activity and selectivity, as well as the fluorescence intensity, of the Pd complexes.

The goal of the work reported here was to amplify the fluorescent properties of 4-aryliden-5(4H)-oxazolones by suppression of the hula-twist non-radiative deactivation pathway. This aim was achieved by simultaneous bonding of a Pd center to the N atom of the heterocycle and the ortho carbon of the arylidene ring. Two different 4-((Z)-arylidene)-2-((E)-styryl)-5(4H)-oxazolones, the structures of which are closely related to the chromophore of the Kaede protein and substituted at the 2- and 4-positions of the arylidene ring (1a OMe; 1b F), were used as starting materials. Oxazolones 1a and 1b were reacted with Pd(OAc)2 to give the corresponding dinuclear orthometalated palladium derivates 2a and 2b by regioselective C–H activation of the ortho-position of the arylidene ring. Reaction of 2a (2b) with LiCl promoted the metathesis of the bridging carboxylate by chloride ligands to afford dinuclear 3a (3b). Mononuclear complexes containing the orthopalladated oxazolone and a variety of ancillary ligands (acetylacetonate (4a, 4b), hydroxyquinolinate (5a), aminoquinoline (6a), bipyridine (7a), phenanthroline (8a)) were prepared from 3a or 3b through metathesis of anionic ligands or substitution of neutral weakly bonded ligands. All species were fully characterized and the X-ray determination of the molecular structure of 7a was carried out. This structure has strongly distorted ligands due to intramolecular interactions. Fluorescence measurements showed an increase in the quantum yield (QY) by up to one order of magnitude on comparing the free oxazolone (QY < 1%) with the palladated oxazolone (QY = 12% for 6a). This fact shows that the coordination of the oxazolone to the palladium efficiently suppresses the hula-twist deactivation pathway.

The ortho-palladated phenylglycine derivative [Pd(µ-Cl)(C6H4C(H)(CO2Me)NH2-C,N)]2 (1) reacts with substituted styrenes R1C6H4CH=CH2 (2a–2f) to give two different compounds as a function of the reaction conditions. When the reaction was performed in chloroform under reflux, the stilbene derivatives [C6H4-1-(CH(CO2Me)(NH2))-2-(E)-(CH=CHC6H4R1)] (3a–3f) were obtained, but when the reaction was carried out in toluene under reflux, the 3-arylisoquinoline-1-carboxylates (4a–4f) were obtained instead. The method has distinct advantages over other methods in that it is simple and general, only one/two reaction steps are necessary to obtain the final product, the prefunctionalisation of the substrates is not mandatory and nor is the presence of ancillary ligands, and a regioselective mono-insertion of the alkenes is systematically observed.