Layer-by-layer self-assembled pyrrole-based donor-acceptor chromophores as electro-optic materials

The synthesis of the heterocycle-based diethanolaminomethyl-functionalized derivative 1-(pyridin-4-yl)-2-[(N-methylpyrrol-2-yl)-5-methylenediethanolamine]ethene (2) from (1-pyridin-4-yl)-2-(N-methyl-pyrrol-2-yl)ethene (1) and their methylpyridinium dyes 1-(N-methylpyridinio)-2-[(N-methylpyrrol-2-yl)-5- methylenediethanolamine]ethene iodide (3) and 1-(N-methylpyridinio)-2-[(N-methylpyrrol-2-yl)-5- methylenediethanolamine]ethene iodide (4) is described. NLO-active chromophore monolayers SA-1 and SA-2 were obtained by reaction of p-iodomethylphenyldiiodochlorosilane (5)-functionalized substrates and dye precursors 1 and 2, respectively. A _χ⁽²⁾ value of ∼120 pm/V is observed for SA-2. The new diethanolaminomethyl-functionalized chromophore 2 is also a suitable building block for the layer-bylayer formation of intrinsically acentric, highly transparent nonlinear optical/electro-optic multilayers (SAS = self-assembled superlattice). The organic SAS films are characterized by a combination of physicochemical methods including synchrotron specular X-ray reflectivity, angle-dependent polarized second-harmonic generation, optical (absorption and photoluminescence) spectroscopy, X-ray photospectroscopy, atomic force microscopy, and advancing contact angle measurements.