RESUMEN
In this report, we describe a modular synthesis approach towards a new series of non-centrosymmetric, dipolar 4,4'-bipyridines bearing 2,6- and 3,5-functionalized pyridyl moieties at the peripheries. Central to our strategy is the selective substitution on only one pyridyl motif that could contain electron-donating (-CH3 ) or electron-withdrawing (-F, -Cl, -CF3 ) groups which causes electronic/steric effects on one nitrogen atom in 4,4'-bipyridines. This synthetic protocol was further applied to prepare azo-functionalized (-N=N-) asymmetric bipyridines and non-centrosymmetric 4,4'-bipyridine N-oxide scaffolds, which overcome the synthetic hurdles oxidizing 4,4'-bipyridines to N-monoxides selectively at only one pyridine. Compared to the conventional symmetrical bipyridines, the dipolar non-centrosymmetric molecular tectons pave the way for the realization of non-centrosymmetric supramolecular assemblies because of the difference in the binding energy of the pyridyl nitrogen atoms.
RESUMEN
Liquid-phase, quasi-epitaxial growth is used to stack asymmetric, dipolar organic compounds on inorganic substrates, permitting porous, crystalline molecular materials that lack inversion symmetry. This allows material fabrication with built-in electric fields. A new programmed assembly strategy based on metal-organic frameworks (MOFs) is described that facilitates crystalline, noncentrosymmetric space groups for achiral compounds. Electric fields are integrated into crystalline, porous thin films with an orientation normal to the substrate. Changes in electrostatic potential are detected via core-level shifts of marker atoms on the MOF thin films and agree with theoretical results. The integration of built-in electric fields into organic, crystalline, and porous materials creates possibilities for band structure engineering to control the alignment of electronic levels in organic molecules. Built-in electric fields may also be used to tune the transfer of charges from donors loaded via programmed assembly into MOF pores. Applications include organic electronics, photonics, and nonlinear optics, since the absence of inversion symmetry results in a clear second-harmonic generation signal.
RESUMEN
Herein, we report the functionalization of the ß-positions of deutero- and protoporphyrin IX dimethyl esters. Initial halogenations were carried out on both deutero- and protoporphyrin IX dimethyl esters. Although previously reported, vastly optimized yields with respect to deuteroporphyrin halogenation were obtained. Methods were developed for the bromination of the vinyl groups of protoporphyin IX dimethyl ester. Subsequent palladium-catalyzed coupling reactions were utilized to modify the periphery of these naturally occurring porphyrin derivatives with a variety of functionalities. The described Suzuki, Sonogashira, and "Click" reactions demonstrate the ease at which these porphyrins may be manipulated and even interchangeable, as will be discussed for one example. X-ray crystallographic analysis successfully determined the structure of two derivatives synthesized. Results identified a unique head-to-tail stacking pattern for 3,8-diphenyldeuteroporphyrin IX dimethyl ester, most likely due to the presence of additional aromatic moieties on the periphery of the porphyrin.