Abstract.Catechols are found in nature taking part in a remarkably broad scope of biochemical processes and functions. Though not exclusively, such versatility may be traced back to several properties uniquely found together in the o -dihydroxyaryl chemical function; namely, its ability to establish reversible equilibria at moderate redox potentials and pHs and to irreversibly cross-link through complex oxidation mechanisms; its excellent chelating properties, greatly exemplifi ed by, but by no means exclusive, to the binding of Fe 3 + ; and the diverse modes of interaction of the vicinal hydroxyl groups with all kinds of surfaces of remarkably different chemical and physical nature. Thanks to this diversity, catechols can be found either as simple molecular systems, forming part of supramolacular structures, coordinated to different metal ions or as macromolecules mostly arising from polymerization mechanisms through covalent bonds. Such versatility has allowed catechols to participate in several natural processes and functions that range from the adhesive properties of marine organisms to the storage of some transition metal ions. As a result of such an astonishing range of functionalities, catechol-based systems have in recent years been subject to intense research, aimed at mimicking these natural systems in order to develop new functional materials and coatings. A comprehensive review of these studies is discussed in this paper.
A facile one-step polymerization strategy is explored to achieve novel catechol-based materials. Depending on the functionality of the catechol, the as-prepared product can be used to modify at will the surface tension of nano and bulk structures, from oleo-/hydrophobic to highly hydrophilic. A hydrophobic catechol prepared thus polymerized shows the ability to self-assemble as solid nanoparticles with sticky properties in polar solvent media. Such a versatile concept is ideal for the development of catechol-based multifunctional materials.
A series of catechol derivatives with a different number of linear alkyl chain substituents, and different length, have been shown to polymerize in the presence of aqueous ammonia and air, yielding hydrophobic coatings that present the ability to provide robust and efficient water repellency on weaved textiles, including hydrophilic cotton. The polymerization strategy presented exemplifies an alternative route to established melanin- and polydopamine-like functional coatings, affording designs in which all catechol (adhesive) moieties support specific functional side chains for maximization of the desired (hydrophobic) functionality. The coatings obtained proved effective in the transformation of polyester and cotton weaves, as well as filter paper, into reusable water-repellent, oil-absorbent materials capable of retaining roughly double their weight in model compounds (n-tetradecane and olive oil), as well as of separating water/oil mixtures by simple filtration.
A novel strategy to achieve thermally switchable photochromism in solid materials is reported, which relies on the preparation of polymeric core-shell capsules containing solutions of photochromic dyes in acidic phase-change materials. Upon changing the phase (solid or liquid) of the encapsulated medium, one of the two photochromic states of the system is selectively stabilized on demand, allowing for reversible interconversion between direct and reverse photochromism when thermally scanning through the melting temperature of the phase-change material. This strategy, which does not require the addition of external agents or chemical modification of the dyes, proved to be general for different spiropyran photochromes and to be applicable to the fabrication of a variety of functional materials by simply embedding the capsules obtained into a solid matrix of choice.
We report here the synthesis, X-ray structures, optical and electrochemical properties, and density functional calculations for new pyrrolopyridazine derivatives. Ten strongly luminescent heterocycles were synthesized by 1,3-dipolar cycloaddition reactions between alkylated pyridazine or cinnoline and naphthoquinone or dimethyl acetylenedicarboxylate (DMAD). They are benzo[f]pyridazino[6,1-a]isoindole-5,10-diones (BPID) 1 − 4, benzo[f]pyridazino[6,1-a]isoindole (BPI) 5, pyrrolo[1,2-b]cinnolines (PC) 6 and 7, and pyrrolo[1,2-b]pyridazines (PP) 8−10. The relative luminescence quantum yield can be as high as 90% and the heterocycles are luminescent in the solid state, which indicates that there is little self-quenching in these systems. Furthermore, we have shown that the optical properties of pyrrolopyridazines can be tuned by substitutions in different ring positions. An unexpected blue shift and a large red shift with a different π conjugation system were explained by aromaticity arguments using DFT calculations and X-ray crystal structures. Electrochemical investigation has shown that the redo potentials of the new heterocycles could be controlled by design. The synthesis of a series of compounds allowed detailed analysis of substituent effects on structures, frontier orbitals, and luminescent and electrochemical properties.
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