Room temperature homeotropic alignment of mixed-stacking columns of H6TP donors and PDI acceptors by charge transfer interactions and size match

Abstract

Room temperature mesophases were achieved by blending donors 2,3,6,7,10,11-hexakis-(hexyloxy)-triphenylene (H6TP) with acceptors N,N′-bis(1-heptyloctyl)-perylene-3,4,9,10-tetracarboxylic diimide (PDI) via charge transfer interactions and size match. Compared with H6TP (mesophase temperature range: 97°C–51°C) and PDI (119°C–108°C), H6TP/PDI=1/2 (138°C - room temperature), 1/1 (139°C–40°C) and 1/0.5 (130°C–31°C) blends showed increase of clearing points and decrease of crystallization temperatures with wide mesophase temperature ranges. Different from edge-on orientation of PDI and no preferred alignment of H6TP, face-on alignments of all mixtures films could be achieved and stable at room temperature by cooling from isotropic state. It was inferred that stabilised columnar mesophases of H6TP/PDI blends were caused by charge transfer (CT) interactions and size match of them in hexagonal columnar phases. The existence of CT interactions was demonstrated by upfield shifts of aromatic protons in the 1H NMR spectra of H6TP/PDI blends solutions and obvious fluorescent quenching in the blends films.