Anisotropic optical properties and structures of block copolymer/silica thin films containing aligned porphyrin J-aggregates

Abstract

Mesostructured silica-block copolymer thin films are demonstrated to provide orientationally ordered host matrixes for stable alignment of coassembled porphyrin J-aggregates with anisotropic optical properties. Visible light at 490 nm was absorbed anisotropically (A(parallel to)/A(perpendicular to) = 1.35) by aligned, hexagonally ordered (ethylene oxide)(20)-(propylene oxide)(70)-(ethylene oxide)(20) (P123) triblock copolymer/silica nanocomposite films containing 1-5 wt% tetrakis(4-sulfonatophenyl)porphyrin (TPPS4) guest species in the form of J-aggregates. Amorphous silica prepared similarly and containing TPPS4 J-aggregates, but without structure-directing block copolymer species, absorbed light isotropically (A(parallel to)/A(perpendicular to) = 1.00). The porphyrin guest species were determined to be preferentially associated with the hydrophilic ethylene oxide moieties of the triblock copolymer, by using two-dimensional (21)) solid-state H-1{H-1} and C-13{H-1} NMR correlation experiments, including under conditions of fast (45 kHz) magic-angle spinning. Interrelationships are shown and established among synthesis conditions, the molecular, mesoscopic, and orientational structural ordering in the porphyrin-containing nanocomposite thin films, and their macroscopic optical properties.