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π‐Conjugated nanoribbons attract interest because of their unusual electronic structures and charge‐transport behavior. Here, we report the synthesis of a series of fully edge‐fused porphyrin‐anthracene oligomeric ribbons (dimer and trimer), together with a computational study of the corresponding infinite polymer. The porphyrin dimer and trimer were synthesized in high yield, via oxidative cyclodehydrogenation of singly linked precursors, using 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) and trifluoromethanesulfonic acid (TfOH). The crystal structure of the dimer shows that the central π‐system is flat, with a slight S‐shaped wave distortion at each porphyrin terminal. The extended π‐conjugation causes a dramatic red‐shift in the absorption spectra: the absorption maxima of the fused dimer and trimer appear at 1188 nm and 1642 nm, respectively (for the nickel complexes dissolved in toluene). The coordinated metal in the dimer was changed from Ni to Mg, using p‐tolylmagnesium bromide, providing access to free‐base and Zn complexes. These results open a versatile avenue to longer π‐conjugated nanoribbons with integrated metalloporphyrin units. [ABSTRACT FROM AUTHOR]

The reactions of N-alkyliminodiacetamide derivatives, namely N-ethyliminodiacetamide (CHCHN(CHCONH); Etimda) and N-isopropyliminodiacetamide (CH)CHN(CHCONH); i-Primda), with sodium tetrachloropalladate(II) in aqueous solutions were investigated. Three new palladium(II) complexes, [Pd(Etimda)]∙2HO ( 1), [Pd( i-Primda)]∙2HO ( 2) and [PdCl( i-Primda)] ( 3), were obtained and characterized by X-ray structural analysis, infrared spectroscopy and thermal analysis (TGA). The square planar coordination environments around the palladium(II) ions in complexes 1 and 2 consist of two N,N′-bidentate N-alkyliminodiacetamidato ligands, with imino N atoms in trans-position. The complex 3 also exhibits a square planar coordination environment around Pd(II), but with two chloride ions and one neutral N-isopropyliminodiacetamide ligand bound in an N,O′-bidentate coordination mode. The described coordination modes, as well as the presence of deprotonated amide groups in ligands in 1 and 2, are found for the first time in palladium(II) complexes with iminodiacetamide type ligands. The molecular geometries and infrared spectra of these three complexes were also modelled using DFT calculations, at the BP86-D3/def2-TZVPP/PCM level of theory. The RMSD values suggest a good agreement of the calculated and experimental geometries. A QTAIM analysis suggests a qualitative correlation between bond lengths and energy densities, also supported by an NBO analysis. The dimer interaction energy between complex units was estimated at about −15 kcal/mol for all complexes. [ABSTRACT FROM AUTHOR]

In this study, the structure of the polycrystalline poly(l,4-phenyleneazine N,N-dioxide) was investigated by Scanning Electron Microscopy and related with the previously calculated molecular structure. Kinetics of polymerization of 1,4-dinitrosobenzene, prepared by both cryogenic UV photolysis and in vacuo deposition were measured by time-resolved FT-IR spectroscopy. Acquired data was analyzed by curve fitting with the standard Avrami-Erofeev and two-step consecutive reactions models. Activation parameters were calculated from Arrhenius and Eyring-Polanyi equations, for both models. The results obtained by using the two models, along with the goodness-of-fit parameters, were compared. It was shown that both bulk-based and reaction-based models can be used to adequately describe solid-state chemical reaction kinetics. Furthermore, a two-step consecutive reactions model is a suitable alternative to the most commonly used Avrami- Erofeev model. [ABSTRACT FROM AUTHOR]

Crystal and molecular structure of poly(1,4-phenyleneazine- N , N -dioxide) (PDNB, 1), obtained from polymerization of 1,4-dinitrosobenzene, is investigated by X-ray powder diffraction (XRPD) and DFT calculations. Starting with the determined crystal structure, we have calculated the electronic structure of the polymer, which reveals that 1 is potentially a wide-bandgap (WBG) semiconductor with a band gap of 2.3 eV. Its calculated electronic spectrum with the absorbance at 400 nm is in good agreement with the experimental data. A highly organized crystal structure with linear chains of polymer indicates possible anisotropic electronic properties that could be useful in molecular photoelectronics (e.g OLEDs). Photolysis of 1 at cryogenic temperatures yields dinitrosobenzene monomers, which re-polymerize at higher temperatures. After this reversible photo-thermal cycle, the starting polymorph of 1 is recovered. Thermal analysis (TG/DSC/DTA) and in situ XRPD measurements show the high thermal stability of 1 until around 150 °C. Image 1 • The crystal structure is determined via X-ray powder diffraction. • The ON-OFF polymerization mechanism is studied at low temperature. • Reversible polymerization always gives the same polymorphic form. • Calculation of electronic properties reveals wide-bandgap semiconductivity. • Thermal analyses and in situ studies show stability up to circa 150 °C. [ABSTRACT FROM AUTHOR]