An innovative method for controlled synthesis of bicomponent monolayer films obtained by reduction of diazonium.

This study presents a novel method based on the electrochemical co-reduction of two aryldiazonium salts, enabling the synthesis of controlled two-component monolayer thin films on carbon in a single step. By introducing a 12-carbon alkyl chain as a spacer between the aryldiazonium function and the functional group, precise control over film thickness and composition was achieved. The alkyl chain effectively standardizes the reduction potential, enabling the equalization of reactivity and precise stoichiometric control. Experimental results from spectroscopic, electrochemical, and X-ray photoelectron spectroscopy analyses validate the effectiveness of the method in controlling the composition of the mixed layers.

Solvent-Free Preparation and Moderate Congruent Melting Temperature of Layered Lead Iodide Perovskites for Thin-Film Formation.

Lead halide 2D hybrid perovskites (HP) have emerged as promising materials for photovoltaic and lighting applications. Solvent-free preparations offer greener route, but require congruent melting of halide perovskite for thin films, which has been demonstrated only for monolayered HP (n=1 of the (A)2 (MA)n-1 Pbn I3n+1 series) at the quite high temperature Tm (Tmelting ) of 171 °C. Here, we report on the solvent-free preparation (n=2, 4), thermal behaviour and melt-processed thin films of a series of HP (GABA)2 (MA)n-1 Pbn I3n+1 (n=1, 2, 4; GABA+ : 4-ammoniumbutyric acid cation). The n=1 and n=2 HP have an exceptional low congruent Tm of 126 °C and 136 °C, respectively, and, for n=1, a very good stability in the molten state. The liquid-solid reaction of molten (GABA)2 PbI4 or (GABA)2 (MA)Pb2 I7 with MAPbI3 in 1/1 (T=130 °C) or 1/2 (T=135 °C) ratio leads to pure phases of the n=2 HP and (GABA)2 (MA)3 Pb4 I11 (n=4, Tm =185 °C), respectively. Melt-processed thin films of n=1, n=2 and n=4 HP have also been prepared.

No more compromise: a facile route towards functionalized surfaces with stable monolayers.

The results reported in this study clearly show that it is possible to easily control the formation of a functional monolayer by spontaneous reduction of an aryldiazonium salt on gold in a single step, mimicking the SAM technique.

Site-selected thionated benzothioxanthene chromophores as heavy-atom-free small-molecule photosensitizers for photodynamic therapy.

Photodynamic therapy is a clinically approved anticancer modality that employs a light-activated agent (photosensitizer) to generate cytotoxic reactive oxygen species (ROS). There is therefore a growing interest for developing innovative photosensitizing agents with enhanced phototherapeutic performances. Herein, we report on a rational design synthetic procedure that converts the ultrabright benzothioxanthene imide (BTI) dye into three heavy-atom-free thionated compounds featuring close-to-unit singlet oxygen quantum yields. In contrast to the BTI, these thionated analogs display an almost fully quenched fluorescence emission, in agreement with the formation of highly populated triplet states. Indeed, the sequential thionation on the BTI scaffold induces torsion of its skeleton reducing the singlet-triplet energy gaps and enhancing the spin-orbit coupling. These potential PSs show potent cancer-cell ablation under light irradiation while remaining non-toxic under dark condition owing to a photo-cytotoxic mechanism that we believe simultaneously involves singlet oxygen and superoxide species, which could be both characterized in vitro. Our study demonstrates that this simple site-selected thionated platform is an effective strategy to convert conventional carbonyl-containing fluorophores into phototherapeutic agents for anticancer PDT.

Synthesis and self-assembly of a penta[60]fullerene bearing benzo[ghi]perylenetriimide units.

A benzo[ghi]perylenetriimide (BPTI) derivative bearing a terminal azido group on the expanded π-conjugated backbone has been synthesized and characterized. This promising photo- and electroactive BPTI motif has been used to obtain an original penta(organo)fullerene as a promising multi-electron acceptor system. Our studies show its self-assembly resulting from aggregation via π-π stacking interaction in solution and in the solid state.

Use of Selective Redox Cross-Inhibitors for the Control of Organic Layer Formation Obtained via Diazonium Salt Reduction.

The controlled electrochemical deposition of a series of four diazonium salts (4-bromobenzene, 4-iodobenzene, 4-methoxybenzene, and 4-diethylaminobenzene diazonium) on carbon surfaces has been achieved by exploiting the use of three redox mediators: 2,2-diphenyl-1-picrylhydrazyl, chloranil, and dichlone. The efficiency of the method rests on a fast redox cross-reaction in the diffusion layer between the diazonium compound and the reduced form of the selected inhibitor, characterized by an outer-sphere electron transfer. The effect of the inhibitor addition in the deposition solution was characterized using electrochemical techniques, X-ray photoelectron spectroscopy, and atomic force microscopy. Near-monolayers are obtained when the potential of the redox mediator is at least 100 mV lower than the reduction potential of the diazonium salt concerned. A judicious choice of the redox entity can allow, via a fine control of the experimental conditions, to modulate the thickness of organic layers by varying the grafting potential.

Controlled diazonium electrografting driven by overpotential reduction: a general strategy to prepare ultrathin layers.

A global and extremely simple strategy to prepare a covalently attached monolayered organic film on a carbon surface is presented. The approach is centered on the strict control of the radical polymerization traditionally observed when aryldiazonium salts are reduced. By exploiting the reductive properties of superoxide ions generated from atmospheric dioxygen at the grafting potential, the diazonium concentration is drastically lowered at the substrate/solution interface, resulting in the formation of ultrathin films. As the presented approach does not require any specific synthesis or any redox mediator addition, and is only diffusion controlled by the dissolved dioxygen, it is suitable for the preparation of a large range of functional surfaces on the nanometric scale.

Direct (Hetero)Arylation Polymerization of a Spirobifluorene and a Dithienyl-Diketopyrrolopyrrole Derivative: New Donor Polymers for Organic Solar Cells.

The synthesis and preliminary evaluation as donor material for organic photovoltaics of the poly(diketopyrrolopyrrole-spirobifluorene) (PDPPSBF) is reported herein. Prepared via homogeneous and heterogeneous direct (hetero)arylation polymerization (DHAP), through the use of different catalytic systems, conjugated polymers with comparable molecular weights were obtained. The polymers exhibited strong optical absorption out to 700 nm as thin-films and had appropriate electronic energy levels for use as a donor with PC70BM. Bulk heterojunction solar cells were fabricated giving power conversion efficiencies above 4%. These results reveal the potential of such polymers prepared in only three steps from affordable and commercially available starting materials.

Thermally induced crystallization, hole-transport, NLO and photovoltaic activity of a bis-diarylamine-based push-pull molecule.

The synthesis of a molecule constituted of two diarylamine-based push-pull chromophores covalently linked via their nitrogen atom is described. Comparison of the electronic properties with the parent monomer shows that dimerization has negligible influence on the electronic properties of the molecule but exerts a dramatic impact on the capacity of the material to self-reorganize. Application of thermal annealing to thin films induces the crystallization under original morphologies, a process accompanied by a partial bleaching of the absorption in the visible range and by a huge increase of hole-mobility. X-ray diffraction data on single crystals reveal the presence of π-stacked organization with a non-centrosymmetric co-facial arrangement of the dipoles which leads to intrinsic 2nd order bulk NLO properties of thin films as evidenced by second harmonic generation under 800 nm laser light. The implications of this thermally induced crystallization on the photovoltaic properties of the material are discussed on the basis of preliminary results obtained on simple bilayer organic solar cells.

Enantiopure versus Racemic Naphthalimide End-Capped Helicenic Non-fullerene Electron Acceptors: Impact on Organic Photovoltaics Performance.

Impact of the enantiopurity on organic photovoltaics (OPV) performance was investigated through the synthesis of racemic and enantiomerically pure naphthalimide end-capped helicenes and their application as non-fullerene molecular electron acceptors in OPV devices. A very strong increase of the device performance was observed by simply switching from the racemic to the enantiopure forms of these π-helical non-fullerene acceptors with power conversion efficiencies jumping from 0.4 to about 2.0 % in air-processed poly(3-hexylthiophene)-based devices, thus highlighting the key role of enantiopurity in the photovoltaic properties.

New Penta(tetrathiafulvalenyl)[60]fullerenes for Supramolecular Materials.

New penta(organo)fullerenes donor-acceptor systems bearing five tetrathiafulvalene recognition units have been synthesized to promote self-assemblies similar in appearance to shuttlecocks nested into each other thanks to the conical host cavity created around the fullerene together with the π-π and electronic interactions.

Fluorescent self-assembled monolayers of umbelliferone: a relationship between contact angle and fluorescence.

Self-assembled monolayers (SAMs) that contain fluorophore units are nowadays widely used to tune surface properties and design new chemical sensor chips. It is well-known that the nature of the substrate may strongly interfere with the emission properties of the grafted molecules, but the organization of the monolayer may also have an important role. To study the influence of the SAM organization on the luminescence properties, we prepared different coumarin-based derivatives endowed with tethered chains of different lengths and elaborated the corresponding SAMs on glass slides. Besides SAM structural characterizations by atomic force microscopy and X-ray reflectivity, we carried out contact angle measurements and applied the Van Oss-Chaudhury-Good theory, which was rarely used previously for self-assembled monolayers. As expected, by increasing the tethered chain length, a higher surface coverage, a higher degree of organization, and a stronger molecular packing were observed. However, it appears to facilitate the self-quenching process, and thus, this strongly affects the fluorescent properties of the SAMs.

Nonlocal communication with photoinduced structures at the surface of a polymer film.

Nonlocal communication between two laser light beams is experimented in a photochromic polymer thin films. Information exchange between the beams is mediated by the self-induction of a surface relief pattern. The exchanged information is related to the pitch and orientation of the grating. Both are determined by the incident beam. The process can be applied to experiment on a new kind of logic gates.