Aggregation-Induced Enhanced Emission of Tetraphenylethene-phenylalanine Hybrids: Synthesis and Characterization.

Aggregation-induced emitting (AIE) luminophores are sensitive and easy-to-handle types of probes that allow driving a stimulus-responsive off/on optical tool through the manipulation of the aggregation behavior. In this work, tetraphenylethene (TPE)-phenylalanine derivatives, characterized by strong aggregation-induced luminescence, were obtained through Suzuki-Miyaura cross-coupling reactions. The reaction proved to be straightforwardly applicable in the single amino acid synthesis as well as in the late-stage peptide functionalization by means of both the classical solution-phase reaction and solid-phase synthesis. A comprehensive structural and analytical investigation highlighted the features driving the self-assembly process and its relationship to AIE efficiency. In particular, we showed that the simple slight (asymmetric) extension of the TPE π-systems results in more efficient and brighter emissions, with respect to the simple TPE system itself.

Sparkling Organic Phosphorescence from Fluorinated Tetrathia[7]helicenes: Synthesis and Photophysical, Electrochemical and Computational Studies.

Structure-property correlations in the thiahelicene family are often not trivial beacuse most of the functional groups present on the helical scaffold modify the conjugation size of the π-system. Selecting fluorine-containing groups to provide strong inductive effects without interacting with low-lying orbitals of the system could be the way to overcome the issue. Here we report a study on three fluorine-functionalized tetrathia[7]helicenes, highlighting interesting correlations between the position of the functional groups and the conjugated skeleton properties. Helicenes Heli-F2 and Heli-CF-F2 were prepared by photoinduced isomerization-electrocyclization (the Mallory photocyclization) of the corresponding fluorinated benzodithienyl-ethenes Alk-F2 and Alk-CF-F2, which were prepared in high yields through stereo-conservative Stille reaction. Notably these helicenes were found to display green phosphorescence around 530-550 nm, and the studies suggest an efficient spin-orbit coupling mechanism in these high-energy triplet nonplanar conjugated molecules. Both helicenes and their precursors were thoroughly characterized by means of optical and electrochemical measurements, while DFT calculations enable a rationale on their structure-property correlations to be defined.

Visible Light-Promoted ß-Functionalization of Carbonyl Compounds in the Presence of Organic Dyes.

Herein, we investigate the use of organic photocatalysts in the visible light-promoted ß-functionalization of carbonyl compounds. In particular, we studied the addition of aliphatic aldehydes to α,ß-unsaturated compounds (ß-Michael addition), and the reaction of cyclic ketones with either ketones (ß-aldol condensation) or imines (ß-Mannich reaction). Among the dyes tested, donor-acceptor cyanoarenes gave the best results, promoting the transformations of interest in moderate to good yields. The reaction scope was investigated on substrates with different steric and electronic properties. Fluorescence quenching analysis (Stern-Volmer experiments) led us to propose for these reactions a reductive quenching mechanism involving a transient 5πe- activation mode.

Photo-Induced Microfluidic Production of Ultrasmall Glyco Gold Nanoparticles.

Ultra-small gold nanoparticles (UAuNPs) are extremely interesting for applications in nanomedicine thanks to their good stability, biocompatibility, long circulation time and efficient clearance pathways. UAuNPs engineered with glycans (Glyco-UAuNPs) emerged as excellent platforms for many applications since the multiple copies of glycans can mimic the multivalent effect of glycoside clusters. Herein, we unravel a straightforward photo-induced synthesis of Glyco-UAuNPs based on a reliable and robust microfluidic approach. The synthesis occurs at room temperature avoiding the use of any further chemical reductant, templating agents or co-solvents. Exploiting 1 H NMR spectroscopy, we showed that the amount of thiol-ligand exposed on the UAuNPs is linearly correlated to the ligand concentration in the initial mixture. The results pave the way towards the development of a programmable synthetic approach, enabling an accurate design of the engineered UAuNPs or smart hybrid nano-systems.

ß-Diketonate ancillary ligands in heteroleptic iridium complexes: a balance between synthetic advantages and photophysical troubles.

ß-Diketones are an important class of bidentate cyclometalating compounds, used in organometallic chemistry as ancillary ligands because of their wide commercial availability and easy synthesis. They are employed to finely tune the electronic, spectroscopic and physical properties of metal complexes. Heteroleptic iridium complexes often benefit from the use of ß-diketonate ligands, their properties being similar to those of the corresponding homoleptic tris-cyclometalated ones. Nevertheless, in some cases, their use results in a complete quenching of the phosphorescence. Aiming to understand the origin of this drawback, we designed a suitable class of heteroleptic complexes and studied their thermal stability (DSC/TGA). We explored the effect of the ancillary ligand in a series of Ir(iii) complexes bearing 2-phenylpyridine (ppy) as a cyclometalated ligand and acac (acetylacetonate), tta (2-thienoyltrifluoroacetonate), dtdk (1,3-di(thiophen-2-yl)propane-1,3-dionate) and BPhen (4,7-diphenyl-1,10-phenanthroline) as ancillary ligands. Through photochemical and electrochemical investigations, whose results agree with and support our density functional theory calculations, we demonstrate that ß-diketonate ligands with low triplet energy generate dark triplet excited states with negligible coupling to the ground state which indeed promote non-radiative relaxation through population of higher states.

Upper limit to the ultimate achievable emission wavelength in near-IR emitting cyclometalated iridium complexes.

Iridium complexes bearing cyclometalated (C^N) ligands are the current emitters of choice for efficient phosphorescent organic light emitting diodes (OLEDs). Homoleptic iridium complexes Ir(C^N)3 and the analogous heteroleptic ones carrying a ß-diketonate ancillary ligand (C^N)2Ir(O^O) often exhibit similar photophysical properties and device performances; the choice among them usually depends both on the yield/ease of the respective synthetic preparations as well as on the device fabrication methods (i.e. vacuum-deposition or solution-process). In our recent study we found a significant spectral red shift on going from the homoleptic to the ß-diketonate Ir(iii) derivatives. The NIR emitting complex Ir(iqbt)2dpm (λmax = 710 nm) has almost 20 nm red shifted emission compared to the homologue Ir(iqbt)3 making only the former a real NIR emitter. For comparison, we studied the Pt(iqbt)dpm complex as the suitable example to investigate metal ligand interactions. Noteworthily the Pt(iqbt)dpm emission perfectly overlaps that of the Ir(iqbt)2dpm. In this paper we provide an in-depth investigation of these systems by electrochemical and spectroscopic analyses and corroborate the results with DFT and TDDFT calculations to investigate whether the Pt(ii) complex can be used as a model system to predict how far the emission can be pushed in a Ir(iii) heteroleptic derivative bearing the same C^N ligand.

4-Connected azabicyclo[5.3.0]decane Smac mimetics-Zn2+ chelators as dual action antitumoral agents.

Putative dual action compounds (DACs 3a-d) based on azabicyclo[5.3.0]decane (ABD) Smac mimetic scaffolds linked to Zn2+-chelating 2,2'-dipicolylamine (DPA) through their 4 position are reported and characterized. Their synthesis, their target affinity (cIAP1 BIR3, Zn2+) in cell-free assays, their pro-apoptotic effects, and their cytotoxicity in tumor cells with varying sensitivity to Smac mimetics are described. A limited influence of Zn2+ chelation on in vitro activity of DPA-substituted DACs 3a-d was sometimes perceivable, but did not lead to strong cellular synergistic effects. In particular, the linker connecting DPA with the ABD scaffold seems to influence cellular Zn2+-chelation, with longer lipophilic linkers/DAC 3c being the optimal choice.

Near-IR Emitting Iridium(III) Complexes with Heteroaromatic ß-Diketonate Ancillary Ligands for Efficient Solution-Processed OLEDs: Structure-Property Correlations.

Three NIR-emitting neutral Ir(III) complexes [Ir(iqbt)2 (dpm)] (1), [Ir(iqbt)2 (tta)] (2), and [Ir(iqbt)2 (dtdk)] (3) based on the 1-(benzo[b]thiophen-2-yl)-isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6-tetramethyl-3,5-heptanedionate; tta=2-thienoyltrifluoroacetonate; dtdk=1,3-di(thiophen-2-yl)propane-1,3-dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR-emitting, solution-processed phosphorescent organic light-emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1) with negligible efficiency roll-off values, exceeding the highest reported values for solution-processible NIR emitters.

The use of chemical actinometry for the evaluation of the light absorption efficiency in scattering photopolymerizable miniemulsions.

Oil-in-water miniemulsions containing a mixture of monomers as the dispersed organic phase have been shown recently to be promising media for the development of photoinitiated polymerization processes. Albeit a crucial factor for a successful application, the efficiency of light absorption by the photoinitiator in these highly scattering systems is difficult to evaluate. In this work, a well-characterized water insoluble chemical actinometer (DFIS) replaced the oil-soluble photoinitiator, and was used as a probe and a model for UV light absorption in miniemulsions of variable droplet sizes and organic phase compositions (i.e. at different levels of scattered light). In the first step, the photon flux absorbed by the actinometer was determined in model miniemulsions based on an inert solvent (ethyl acetate), at a low oil phase content (3.0-6.0 wt%). For these low to moderately scattering systems, the photon flux absorbed by the actinometer in the miniemulsions was comparable to that in a homogeneous solution of ethyl acetate. In the second step, the absorbed photon flux was investigated in photopolymerizable miniemulsions (a mixture of acrylate monomers as oil phase). Surprisingly, in spite of much higher scattering coefficients than those found for ethyl acetate based miniemulsions of otherwise the same composition, the photon flux absorbed by the actinometer in photopolymerizable miniemulsions showed only a small decreasing trend. Such a result may be considered favorable for the further development of applications of photopolymerizations in miniemulsions.

A triplet-triplet annihilation based up-conversion process investigated in homogeneous solutions and oil-in-water microemulsions of a surfactant.

The triplet-triplet annihilation based up-conversion process, involving a platinum octaethyl-porphyrin (PtOEP) as a sensitizer and tetraphenyl-pyrene (TPPy) as an emitter, has been investigated in homogeneous solutions of toluene, bromobenzene and anisole, and oil-in-water microemulsions of the TX-100 surfactant, where toluene constitutes the non-polar phase. In homogeneous solutions, the highest up-conversion quantum yield (of the order of 20%) has been achieved in toluene, being the solvent that has the lowest viscosity among those explored. The up-conversion emission from the PtOEP-TPPy pair has been then investigated in a toluene based oil-in-water microemulsion at three different concentrations of the solutes, showing quantum yields up to the order of 1%, under the same irradiation conditions, but different deoxygenating procedures. The results herein reported might represent a good starting point for a future investigation in microheterogeneous systems. An optimization of the microemulsion composition, in terms of surfactant, co-surfactant and toluene concentrations, could allow us to increase the sensitizer and emitter concentrations and set up the best operative conditions to obtain even higher up-conversion efficiencies.

Tetraphenylethylene-Based Photoluminescent Self-Assembled Nanoparticles: Preparation and Biological Evaluation.

The conjugation of tetraphenylethylene (TPE) with podophyllotoxin, N-desacetylthiocolchicine, and cabazitaxel through a sebacic acid linker led to the formation of fluorescent nanoparticles. Dynamic light scattering (DLS) and photoluminescence spectroscopy were used for the identification and characterization of the fluorescent nanoparticles. The biological evaluation was determined in three human ovarian (KURAMOCHI, OVCAR3, OVSAHO) and three human breast (MCF7, SKBR 3, and MDA-MB231) cancer cell lines. In the case of cabazitaxel, the nanoparticles maintained the activity of the parent drug, at the low nanomolar range, while exhibiting high blue fluorescence. The internalization of the fluorescent NPs into cells was detected using immunofluorescence assay.

Ab Initio Many-Body Perturbation Theory Calculations of the Electronic and Optical Properties of Cyclometalated Ir(III) Complexes.

Cyclometalated Ir(III) compounds are the preferred choice as organic emitters in organic light-emitting diodes. In practice, the presence of the transition metal surrounded by carefully designed ligands allows fine-tuning of the emission frequency as well as good efficiency of the device. To support the development of new compounds, experimental measurements are generally compared with absorption and emission spectra obtained from ab initio calculations. The standard approach for these calculations is time-dependent density functional theory (TDDFT) with a hybrid exchange-correlation functional like B3LYP. Because of the size of these compounds, the application of more complex quantum chemistry approaches can be challenging. In this work, we used many-body perturbation theory approaches, in particular the GW approximation with the Bethe-Salpeter equation (BSE) implemented in Gaussian basis sets, to calculate the quasiparticle properties and the absorption spectra of six cyclometalated Ir(III) complexes, going beyond TDDFT. In the presented results, we compared standard TDDFT simulations with BSE calculations performed on top of perturbative G0W0 and accounting for eigenvalue self-consistency. Moreover, in order to investigate in detail the effect of the DFT starting point, we concentrated on Ir(ppy)3 and performed GW-BSE simulations starting from different DFT exchange-correlation potentials.

Vacuum-Deposited Porphyrin Protective Films on Graphite: Electrochemical Atomic Force Microscopy Investigation during Anion Intercalation.

The development of graphene products promotes a renewed interest toward the use of graphite in addition to the historical one for its proven viability as battery electrode. However, when exposed to harsh conditions, the graphite surface ages in ways that still need to be fully characterized. In applications to batteries, to optimize the electrode performances in acid solutions, different surface functionalizations have been studied. Among them, aromatic molecules have been recently proposed. In this communication, we report on the protective effect exerted by a physical-vapor-deposited porphyrin layer. Metal-free tetra-phenyl-porphyrins were deposited on a highly oriented pyrolytic graphite crystal to study the modifications that occur during anion intercalation in graphite. The graphite electrode was plunged in an electrolyte solution of 1 M sulfuric acid and subjected to cyclic voltammetry. The results indicate that blister formation, the characteristic swelling of graphite surface induced by anion intercalation, is significantly perturbed by the porphyrin overlayer; the process is inhibited in those areas where the protective porphyrin film is present. We ascribe the inhibition of the anion intercalation to the protective porphyrin wetting layer.