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-by-layer 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.