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Helicenes combine two central themes in chemistry: extended π-conjugation and chirality. Heteroatom doping preserves both characteristics and allows to modulate the electronic structure of a helicene. Herein, we report the (BO)2-doped tetrathia[7]helicene 1, which was prepared from 2-methoxy-3,3'-bithiophene via four steps. 1 is formally derived by substituting two (Mes)B-O moieties in place of (H)C=C(H) fragments in two benzene rings of parent tetrathia[7]helicene. X-ray crystallography revealed a dihedral angle of 50.26(9)° between the two terminal thiophene rings. (P)-/(M)-1 enantiomers were separated by chiral-HPLC and are configurationally stable at room temperature. The experimentally determined enantiomerization barrier of 27.4 ± 0.1 kcal mol-1 is lower than that of tetrathia[7]helicene (39.4 ± 0.1 kcal mol-1). Circular dichroism spectra of (P)- and (M)-1 show a perfect mirror-image relationship. 1 is a blue emitter (λem = 411 nm) with a photoluminescence quantum efficiency of ΦPL = 6% (cf. tetrathia[7]helicene: λem ≈ 405 nm, ΦPL = 5%).

Efficient and versatile synthetic routes to functionalized tetrathia[7]helicenes (7-THs) are described. The key intermediates of these methodologies are 2-bromo-3,3?-bibenzo[1,2-b:4,3-b?]dithiophenes (1), synthesized through a palladium-catalyzed homocoupling reaction between two benzo[1,2-b:4,3-b?]dithiophene units followed by a regioselective ?-bromination. Direct palladium-catalyzed annulation of bromides 1 with internal alkynes provides a set of 7,8-disubstituted 7-THs 2 in moderate to good yields (46-80 %). Otherwise, 7-monosubstituted 7-THs 4 have been prepared through Sonogashira coupling of 1 with terminal alkynes, followed by platinum- or indium-promoted cycloisomerization of alkynyl intermediates 6. Finally, the versatility of bromides 1 has also been demonstrated by using them for the preparation of benzo (hetero) fused 7-TH derivatives 7 via Suzuki coupling with (hetero)arylboronic acids and the photocyclization of the obtained intermediates 9.

We have studied the photophysics of tetrafurylethene, an aggregation-induced emission luminogen with exceptionally short intramolecular O-O distances of 2.80 Å and a significant red-shifted morphochromism (27 nm) when going from the aggregate to the crystal. The short O-O distances, which are substantially smaller than the sum of the van der Waals radii (3.04 Å), are due to the fact that the oxygen atoms act as an electronic bridge connecting the furan rings on opposite ends of the central double bond, giving rise to a circular delocalization of the π-electron density across the rings. In the excited state the O-O distance is further reduced to 2.70 Å; the increased O-O interaction causes a narrowing of the HOMO-LUMO gap, resulting in the red morphochromism of the emission. Our results show the structural origin of the red-shifted emission lies in close O-O contacts, paving the way for understanding the clusteroluminescence of oxygen-rich non-conjugated systems that emit visible light.

beta-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 -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 -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.

a detailed electrochemical and photophysical comparative study of three parallel series of phenyl, thienyl and furyl substituted ethylenes has been carried out, implemented by the computational calculation of selected terms. Relationships have been highlighted between molecular structure (number and type of aromatic rings) and important functional properties (in particular, electronic features and oligomerization ability). Interestingly, some of the studied heteroaryl-ethylenes show emission in the solid state displaying an aggregation-induced emission behavior.

A lys-GTAGATCACT-lys peptide nucleic acid (PNA) decamer labelled with the luminescent 2,3-diphenyl maleimido (DPM) group on the e-position of the terminal lysine residue was prepared through an automated solid phase synthesis. Fluorescence emission of the DPM-labelled PNA thus obtained was found to be significant and promising for the potential application in DNA recognition.

Square planar platinum complexes are an important class of compounds used in (nano)technology, optoelectronics, medicinal chemistry and catalysis. The major research interests in cyclometalated Pt(ii) complexes focus on the selective modulation of their electronic properties and the control of the (cis/trans) geometry. For the first time, we unveil and demonstrate that cis-trans isomers of Pt(ii) complexes can be obtained in a derivative carrying the 1-phenyl-pirazolate (Hppz) and 2-hydroxy-1-naphtyl-(N-phenyl)imine ligands. The two isomers display significant differences in both optical and electronic properties. While luminescence is quenched in solution, they are brightly emissive in the PMMA matrix at room temperature and in the 2MeTHF rigid matrix at 77 K. The phosphorescent emission of the cis isomer, blue-shifted compared to that of the trans one, results from the significantly different trans influence of the ppz ligand. Theoretical investigation highlights the almost isoenergetic potential energy of the two isomers therefore explaining their formation and evidences a large geometry distortion of their triplet state, which should be responsible for the observed luminescence efficiency.

We have synthesized a series of tetra(2-thienyl)ethylene (TTE) derivatives, selectively functionalized at the thiophene α positions, either by a coupling procedure or by direct electrophilic substitution of the TTE system. Optical spectroscopy revealed that TTE shows orange emission (470 nm) in a diluted 2-MeTHF matrix at 77 K and blue (420 nm) aggregation-induced emission (AIE) in the solid state. An exhaustive electrochemical study afforded a full rationalization of the electronic properties in terms of the HOMO and LUMO energy levels and gaps, as well as localization and features of the redox centers with respect to TTE functionalization.

Two new metal-free organic dyes, CR29 and CR52, with high extinction coefficients in the visible spectral region between 400–650 nm, have been synthesized. The donor–acceptor structure of the dyes feature benzodithiophene moieties BDT1 and BDT as rigid π-conjugated spacers, which have so far been very little studied for dye-sensitized solar cell (DSSC) applications. DFT/TDDFT calculations have been employed to guide the design of the chromophores as well as to shed light on their electronic and optical properties. Photophysical and electrochemical characterization studies have been carried out to gather information on the charge transfer processes occurring at the dye–semiconductor interfaces. Under standard AM 1.5 conditions, DSSC sensitized with CR29 showed good conversion efficiencies: 5.14 % in the liquid electrolyte cell setup and 2.47 % in the solid-state DSSC.

Carboxy-terminated polyvinylpyrrolidin-2-one (PVP) has been used as a new water-soluble and biocompatible polymeric support for a series of ferrocene labeled amino acid and peptide nucleic acid (PNA) monomer derivatives 4 – 7 . The organometallic polymer-conjugates thus obtained are new and potentially useful as water-soluble electrochemically active probes for biomolecules. In view of such application, their electrochemical activity has been evaluated and has proved very high notwithstanding the complexity and bulkiness of the molecule, affording detection limits down to 10 −8 M in the aqueous medium.

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.

A series of pushepull triarylamine organic dyes containing the benzo[1,2-b:4,5-b0]dithiophene unit as a spacer and bearing alkyl chains in different positions of the molecule were synthesized. The new dyes 1 e4 were characterized by optical and electrochemical measurements and density functional theory calculations and used as sensitizers in liquid dye-sensitized solar cells. The effect of alkyl chain position on dye properties and performances was investigated and dye 1, bearing two 3,7-dimethyloctyl groups on the benzodithiophene core, exhibited the best behaviour in term of light absorption and cell performance (PCE of 6.6%, to be compared with a PCE of 8.1% for N719-based device). The efficiency of the DSSC was highly dependent on the solvent used for the dye-sensitizing bath, which affects the position of the COOH/COO equilibrium. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction In recent years metal-free organic dyes for DSSC [1e4] have been the object of a growing interest by organic chemists, because a great number of diverse structures can be easily prepared using well established synthetic methodologies and, through appropriate molecular design, their optical, electronic and electrochemical properties can be finely modulated [5e7]. The most efficient metalfree dyes for DSSC are characterized by a pushepull structure in which an

The synthesis of new functionalized 1,2-bis(benzodithienyl)ethenes as well as the preparation of the new tetrathia[7]helicenes are described. The helicenes reported are new chiral push-pull molecules, with potential application in optoelectronics.

We have designed and synthesised a new organometallic molecule containing three ferrocene groups for use as a highly sensitive electrochemical marker in biological assays. This trisferrocene derivative was conjugated to different PNA monomers, and the electrochemical activities of the conjugates were extensively investigated in organic solvents, in view of their potential diagnostic applications. The results showed that the introduction of a trisferrocene unit on the PNA monomer triples the current signal in comparison with the monoferrocene-labelled one. Despite their greater molecular molecular complexity, trisferrocene-conjugated PNA monomers are even more electrochemically active than the reference ferrocene. By using differential pulse voltammetry (DPV), the detection limit can reach 10-8 M in acetonitrile solution. These results are a good premise for the use of the trisferrocene unit as an effective electrochemical probe for biomolecules.

A new chiral ferrocene-labelled tyrosine PNA monomer 1 has been synthesised in good yield in both racemic and enantiomerically pure forms. It is suitable for insertion in various positions of PNA oligomers, a possibility that has been preliminarily demonstrated by synthesising the dimer 16. Moreover, in view of possible applications to nucleic acid detection, a preliminary voltammetric investigation on the electrochemical activity of monomer 1 and its synthetic precursors has been carried out in DMF. It appears that, despite the bulkiness of the PNA monomer backbone, its insertion on the ferrocene group only moderately lowers the latter’s diffusion coefficients and peak currents, thus affording voltammetric detection limits in the order of 10 −6 –10 −7 M.

The addition of the enolate, generated from the tetracarbonylethyl(hydrazino)carbene chromium complex 6 , to achiral enones and aldehydes gave the corresponding Michael and aldol adducts in very high chemical yield and d.e.. Some of the new δ-keto and β-hydroxy hydrazino carbene complexes have been oxidised to give the corresponding hydrazides in high yield. A spectroscopic study to establish the geometry of the enolate generated from 6 has also been performed.

Different arene Cr(CO)(3) complexes were supported on a polystyrene isonitrile resin by photochemical-promoted replacement of a chromium carbonyl ligand by the NC group. The supported complexes proved to be stable and were successfully used for further transformations. In particular, the reactivity of dichlorobenzene complexes to different nucleophiles was investigated and found to be comparable with that of the parent Cr(CO)(3) complexes.

The synthesis, through a cross-metathesis reaction, of the first chiral peptide nucleic acid (PNA) monomer labelled with a Fischer-type carbene complex of chromium is reported. IR analysis of the new bioconjugate shows that the Cr(CO) 4 moiety represents a suitable spectroscopic probe for diagnostic purposes.

A new, high-yielding methodology for reducing hydrazones to hydrazines is described, which allows the synthesis of different mono-, di- and trisubstituted hydrazines. Moreover, the reduction step can be followed by an in situ reaction with a carboxylic acid making possible a ‘one-pot’ synthesis of trisubstituted hydrazides. The method is relatively general and, in principle, suitable for industrial applications.

[reaction: see text] Ugi condensation was used to synthesize the first examples of chiral racemic Ar.Cr(CO)(3) labeled peptide nucleic acid (PNA) monomers bearing the organometallic moiety linked to the alpha-carbon of the glycine unit.

[reaction: see text] We report new, high-yield methodologies for oxidizing Fischer carbenes, particularly hydrazinocarbene complexes. The reagents traditionally used to oxidize Fischer carbenes have failed because of the stability of hydrazinocarbene complexes and the easy oxidation of formed hydrazides in the reaction conditions. The three newly developed methodologies are very mild, fast, efficient, and complementary. Differently functionalized hydrazinocarbene complexes can be oxidized to afford new hydrazides.

The ZnCl 2 -promoted cycloaddition of a series of enantiopure ortho -substituted benzaldehyde–Cr(CO) 3 complexes and Danishefsky's diene gave the corresponding 2-aryl pyranones in good yields and complete enantiospecificity. Some of the mechanistic aspects of the cycloaddition were investigated and the reaction extended to different dienes.

The electrophilic property of metallocarbenes of Fischer-type was used to label amino acid derivatives and a model protein in a regio-specific manner with a transition heavy metal complex. Hence, the reaction of (CO) 5 WC(OMe)Me ( 1 ) was shown to involve exclusively the amino group of a series of α-amino esters whether this function was carried by the α-carbon or by the side chain, leading to stable aminocarbenes. With a model protein, namely bovine serum albumin, labelling also occurred involving solely the amine function of some of its lysine residues. Coupling yield was shown to depend both on the pH where the reaction was carried out, and on the quantity of carbene. This work could find an application in the field of protein X-ray crystallography.

We carried out a highly stereoselective Michael addition (96% de ) of nitromethane to enantiomerically pure tricarbonyl(ethyl-4-chloro-2-trimethylsilylcinnamate)chromium(0). This reaction is the key step in the synthesis of ( R )-(−)-baclofen, a potent antispastic drug.

The antispastic drug ( R )-(−)-baclofen has been synthesized enantioselectively using a diastereoselective Michael addition reaction of the conjugate base of an enantiopure Fischer-type amino carbene to p -chloro-nitrostyrene.

Highly stereoselective allylation of a series of chiral tricarbonylchromium benzaldimine complexes (2a-c) was achieved at -20 degrees C and homoallyl amine complexes (4a-c) were isolated in good yields. In the case of homoallyl amine 4c, obtained in 75% d.e., the degree of stereoselection depends on the catalyst and the reaction conditions. The crystal structure of the major diastereoisomer of racemic 4c was determined by X-ray diffraction, which showed a (S,S) or (R,R) configuration, in agreement with the stereochemical model operating for the ortho-substituted tricarbonylchromium arene complexes. Furthermore, the new tricarbonylchromium complex of N-(2-methoxybenzyliden)diphenyl phosphinamide 3 was prepared. This substrate is a stable analog of the normally unviable ammonia imine. (C) 2000 Elsevier Science S.A. All rights reserved

The reaction of (−)1R or (+)-1S-tricarbonyl(2-substituted benzaldehyde)chromium complexes with tertbutylmethanesulfonamide dianion afforded, after decomplexation and intramolecular cyclization, the enantiomerically pure N-tert-butyl-3-(2-phenyl substituted)-1,2-thiazetidine 1,1 dioxide derivatives. The hydrolytic ring opening gave the corresponding enantiopure β-aminosulfonic acid.

A series of N-arylindoles were obtained in good yields and under mild conditions by nucleophilic substitution reaction of the sodium salt of indole on various haloarene chromium tricarbonyl complexes.

We have synthesized a series of tetra(2-thienyl)ethylene (TTE) derivatives, selectively functionalized at the thiophene ? positions, either by a coupling procedure or by direct electrophilic substitution of the TTE system. Optical spectroscopy revealed that TTE shows orange emission (470 nm) in a diluted 2-MeTHF matrix at 77 K and blue (420 nm) aggregationinduced emission (AIE) in the solid state. An exhaustive electrochemical study afforded a full rationalization of the electronic properties in terms of the HOMO and LUMO energy levels and gaps, as well as localization and features of the redox centers with respect to TTE functionalization.

Enantiomerically pure (-)-(1R)-tricarbonyl-(2-methoxybenzaldehyde)chromium reacts with 2-mercaptobenzylalcohol to give the corresponding diastereomeric thioacetal complexes, which are separated and transformed quantitatively into the enantiomerically pure thioacetals (+)- and (-)-5 by removing the chromium tricarbonyl moiety. Copyright (C) 1996 Published by Elsevier Science Ltd

Different PNA decamers have been appended to a luminescent [Re 2(μ-Cl) 2(CO) 6(μ-1,2-diazine)] complex, to obtain conjugates suitable for cellular imaging. The new compounds can be dissolved in water in the presence of an amount of DMSO as small as 0.4-0.6 mol %. The conjugation with PNA did not perturb the photoluminescence behavior of the organometallic fragment: emission from 3MLCT excited states, centered at ca. 610 nm, was observed, with satisfactory photoluminescence quantum yields (Φ = ca. 0.01, in aerated water). Moreover, the emission could be stimulated also by two-photon excitation. Experiments of cell uptake, performed with different cell lines and under different experimental conditions, showed that the nature of the PNA oligomer strongly affects the biointeraction, while no major differences were observed among the cell lines investigated. The Re-PNA conjugates containing neutral PNA decamers (either homothymine or a standard sequence of the four nucleobases) showed a marked tendency to concentrate in the nuclear region, whereas nucleus penetration was more difficult for the free dirhenium complex. Staining of nucleus and cytoplasm with different colors was generally observed. No nucleus penetration was instead observed for a water-soluble Re-PNA homothymine decamer end-capped with four lysine residues, which localized in endosome-like compartments. © 2012 American Chemical Society.

A gold-nanostructured surface has been obtained by stable deposition of chemically synthesized gold nanoparticles (2.1-5.5 nm size range) on a gold substrate through a dithiol linker. The method proposed for the obtainment of the nanostructure is suitable for the further stable anchoring of a peptide nucleic acid oligomer through four amine groups of lysine terminal residues, leading to fairly reproducible systems. The geometric area of the nanostructured surface is compared with those of a smooth and of an electrochemically generated nanostructured surface by depositing a probe bearing an electrochemically active ferrocene residue. Despite the area of the two nanostructures being quite similar, the response toward a 2 nM target oligonucleotide sequence is particularly high when using the surface built up by nanoparticle deposition. This aspect indicates that morphologic details of the nanostructure play a key role in conditioning the performances of the genosensors.

A homothymine PNA decamer bearing four lysine residues has been synthesized as a probe for the development of amperometric sensors. On one hand, the four amino groups introduced make this derivative nine times more soluble than the corresponding homothymine PNA decamer and, on the other hand, allow the stable anchoring of this molecule on Au nanostructured surface through the terminal -NH 2 moieties. In particular, XPS and electrochemical investigations performed with hexylamine, as a model molecule, indicate that the stable deposition of primary amine derivatives on such a nanostructured surface is possible and involves the free electron doublet on the nitrogen atom. This finding indicates that this PNA derivative is suitable to act as the probe molecule for the development of amperometric sensors. Thanks to the molecular probe chosen and to the use of a nanostructured surface as the substrate for the sensor assembly, the device proposed makes possible the selective recognition of the target oligonucleotide sequence with very high sensitivity.

Researches focused on the development of new organic materials, displaying high carrier mobility, strong optical absorptions and efficient luminescent emissions, are urging for optoelectronic applications such as OLEDs, non linear optics, OFETs, photodetectors and OPV. Organic polyconjugated systems (both small molecules and polymers) as well as polycyclic fused aromatic hydrocarbons represent a fundamental class of molecules whose electronic properties and solid state intermolecular interactions can be varied over a wide range, upon proper functionalization of the ?-scaffold. Tetrathia[7]helicenes, [7]THs, are chiral polycyclic aromatic compounds with nonplanar screw-shaped skeletons formed by ortho-fused benzene and thiophene rings. To investigate their structure-property relationships, we have prepared and studied three new fluorinated [7]TH. In the present communication we report on the synthesis of fluorinated rac-[7]THs; their photophysical and electrochemical properties are compared to the ones of a parent [7]TH. [7]THs display deep blue fluorescence emissions with 10% QY. Low temperature photoluminescence studies reveal the green phosphorescence emission, being located at ca. 540 nm, of the helicene systems never observed before; the significantly high triplet energy emissions in the helicenes is quite unusual considering the size of the conjugated ?-system (featuring 7 ortho-condensed rings). The fast radiative phosphorescence decay in the order of 100 ms, its bright intensity, as well as the small S1-T1 gap (ca. 6000-7000cm-1) are suggestive of a quite efficient spin orbit coupling mechanism affecting the excited state dynamics of these non planar conjugated molecules. Preliminary theoretical TD-DFT investigation will be presented as well.

Le celle DSSC sono celle fotovoltaiche in cui un cromoforo ancorato a TiO2 come semiconduttore, assorbe la luce solare generando corrente elettrica. La nostra ricerca ha riguardato la progettazione e la sintesi di nuovi cromofori organici a base benzoditiofenica, di cui sono state valutate sia le caratteristiche optoelettroniche che le prestazioni in prototipi di celle DSSC da laboratorio.