Strategies for electrooptic film fabrication. Influence of pyrrole-pyridine-based dibranched chromophore architecture on covalent self-assembly, thin-film microstructure, and nonlinear optical response

The new dibranched, heterocyclic "push-pull" chromophores bis{1-(pyridin-4-yl)-2-[2-(N-methyl-pyrrol-5-yl)]ethane}methane (1), 1-(pyrid-4-yl)-2-(N-methyl-5-formylpyrrol-2-yl)ethylene (2), {1-(N-methylpyridinium-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane} {(1-(pyridin-4-yl)-2-[2-(N-methylpyrrol-5-yl)]ethane}-methane (3), N-methyl-2-[1-(N-methylpyrid-4-yl)ethen-2-yl]-5-[pyrid-4-yl]ethen-2-yl]pyrrole iodide (4), bis-{1-(N-methyl-4-pyridinio)-2-[2-(N-methylpyrrol-5-yl)]ethane} methane iodide (5), and N-methyl-2,5-[1-(N-methylpyrid-4-yl)ethen-2-yl]pyrrole iodide (6) have been synthesized and characterized. The neutral (1 and 2) and monomethyl salts (3 and 4) undergo chemisorptive reaction with iodobenzyl-functionalized surfaces to afford chromophore monolayers SA-1/SA-2 and SA-3/SA-4, respectively. Molecular structures and other physicochemical properties have been defined by ¹H NMR, optical spectroscopy, and XRD. Thin-film characterization by a variety of techniques (optical spectroscopy, specular X-ray reflectivity, atomic force microscopy, X-ray photoelectron spectroscopy, and angle-dependent polarized second harmonic generation) underscore the importance of the chromophore molecular architecture as well as film growth method on film microstructure and optical/electrooptic response.