Nanoscale Refractive Index Tuning of Siloxane-Based Self-Assembled Electro-Optic Superlattices

The refractive indices of self‐assembled organic electro‐optic superlattices can be tuned by intercalating high‐Z optically transparent group 13 metal oxide sheets into the structures during the self‐assembly process. Microstructurally regular acentricity and sizable electro‐optic responses are retained in this straightforward synthetic procedure. This “one‐pot” all wet‐chemistry approach involves: i) layer‐by‐layer covalent self‐assembly of intrinsically acentric multilayers of high‐hyperpolarizability chromophores on inorganic oxide substrates, ii) protecting group cleavage to generate a large density of reactive surface hydroxyl sites, iii) self‐limiting capping of each chromophore layer with octachlorotrisiloxane, iv) deposition of metal oxide sheets derived from THF solutions of Ga(OiC3H7)3 or In(OiC3H7)3, and v) covalent capping of the resulting superlattices. An efficient approach to the assembly of organic–inorganic hybrid electro‐optic (EO) superlattices, having refractive indices tunable over a significant and useful range, is demonstrated. This solution‐based deposition of high‐Z metal oxide layers is suitable for nanometer scale film construction with vertical organization of the microstructure and represents a new approach to metal‐ dependent modification of superlattice physicochemical properties. Importantly, no specially designed ligand systems of metal ion scaffolds are necessary.