Thioethyl Porphyrazines: Attractive Chromophores for Second-Order Nonlinear Optics and DSSCs

The first study on the second-order NLO properties of unconventional push-pull systems constituted by asymmetrically monoaryl-substituted thioalkyl porphyrazines, carried out by EFISH measurements and DFT calculations, is here reported. The results obtained show that the porphyrazine macrocycle behaves as a better electron donor and acceptor with respect to structurally similar porphyrin and phthalocyanine tetrapyrroles. Noteworthy, the highest quadratic hyperpolarizability (β1907) values are displayed by the pyrene-substituted thioalkyl porphyrazines, both as free-base and as PdII complex, without the presence of either electron-withdrawing or electron-donating groups. In these cases, the pyrene moiety behaves as an electron-donating group, giving rise to charge transfer HOMO-LUMO electronic transitions. These outcomes show, for the first time, the great potential of the thioalkyl porphyrazine macrocycles for second-order NLO applications. Moreover, the hydroxyphenyl-substituted porphyrazine 2 dye has been also tested as a sensitizer in a TiO2-DSSC, representing the second example reported so far of a DSSC with thioalkyl porphyrazines

Porphycene Protonation: A Fast and Reversible Reaction Enabling Optical Transduction for Acid Sensing

Nano-sensor materials, especially if they target biological purposes, require fine control and tuning of the properties at the molecular scale when intramolecular properties have to be exploited, for example, in optical sensors. By means of optical spectroscopies (namely, spectrophotometry, spectrofluorimetry, and surface differential reflectivity), we demonstrate that thin films of porphycene show a spectacular chromatic change when exposed to acid vapors (specifically to hydrochloric acid). After exposure, the original optical properties of the porphycene films are recovered within a few seconds and without any thermal annealing. In addition, since clear spectroscopic signatures are observed both in absorption and in reflectivity, the parent porphycene is shown to be suitable even for deposition of films onto opaque substrates. These findings are of significant interest in view of potential engineering of the molecules and implementation in devices

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

Iridium complexes bearing cyclometalated (C 27N) ligands are the current emitters of choice for efficient phosphorescent organic light emitting diodes (OLEDs). Homoleptic iridium complexes Ir(C 27N)3 and the analogous heteroleptic ones carrying a \u3b2-diketonate ancillary ligand (C 27N)2Ir(O 27O) 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 \u3b2-diketonate Ir(iii) derivatives. The NIR emitting complex Ir(iqbt)2dpm (\u3bbmax = 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 27N ligand

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

\u3b2-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 \u3b2-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 \u3b2-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

Customised porphyrin coating films for graphite electrode protection: An investigation on the role of peripheral groups by coupled AFM and cyclic voltammetry techniques

Controlling the molecular arrangement of properly designed materials is the ultimate target of studies in surface protection by organic thin films. The properties of the films are even more critical when the protection ability must be match with the function of the underneath active surface as in the case of electrodes covered by suitable protective as well conductive materials. In this context, we demonstrate that the electrode protection against anion intercalation, exerted by a vacuum deposited thin film of meso-tetraphenylporphyrin (H2TPP) on a highly-oriented pyrolytic graphite (HOPG) electrode, can be maximized by tailoring the peripheral groups of the porphyrin skeleton. From atomic force microscopy and cyclic voltammetry investigations, our results highlight the important role played by the molecular/electronic structure of the porphyrins to enhance the molecule-substrate interaction and the molecular assembly in the case of a perfluorinated derivative, thus resulting in effective protection ability in acid environment outperforming theH2TPP film

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

Sonocatalysis: a potential sustainable pathway for the valorization of lignocellulosic biomass and derivatives

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