Nanoscale consecutive self-assembly of thin-film molecular materials for electrooptic switching. Chemical streamlining and ultrahigh response chromophores

A broadly applicable approach to formation of self-assembled organic electrooptic superlattices for high-speed switching is reported. This two-step "one-pot" method involves (i) layer-by-layer covalent self-assembly of intrinsically acentric monolayers of a new high-hyperpolarizability donor-acceptor aminophenylbenzothiazolpyridinium chromophore (β(0.65 eV)_calcd = 1620 × 10^-30 cm⁵ esu^-1) on hydrophilic substrates and (ii) in-situ chromophore deprotection concurrent with self-limiting "capping"/planarization of each chromophore layer with octachlorotrisiloxane. The resulting organic films are characterized using a combination of physicochemical methodolgies including synchrotron X-ray specular reflectivity, angle-dependent polarized second harmonic generation spectroscopy, optical spectrometry, X-ray photoelectron spectroscopy, and advancing contact angle measurements. The superlattices exhibit very large second-order responses, χ⁽²⁾ ≈ 370 pm/V, and a large macroscopic electrooptic coefficient, r₃₃ ≈ 120 pm/V, is estimated at λ₀ = 1064 nm.