Non-Covalent Supramolecular 1D Alternating Copolymer in Crystal toward 2D Anisotropic Photon Transport

Abstract

To realize organic integrated optoelectronic circuits, there is a need for anisotropic optical waveguides at the micro/nanoscale. Anisotropic alignment of one-dimensional-ordered supramolecular structures composed of light-emissive π-conjugated molecules in a crystal may meet the requirements of such waveguides. Here, a bipyridyl-appended acrylonitrile-based π-conjugated molecule was designed, which produced a one-dimensional supramolecular polymer constructed through non-covalent bonding between a lone pair in bipyridyl and a σ-hole in 1,4-diiodo-2,3,5,6-tetrafluorobenzene. The one-dimensional copolymer of bipyridyl and 1,4-diiodo-2,3,5,6-tetrafluorobenzene is aligned horizontally with the two-dimensional crystal surface because of the angle-controlled supramolecular synthons. As a result of control over the non-covalent bonding direction, anisotropic photoluminescence and photon transport (optical waveguiding) characteristics are realized by orienting the transition dipole moment horizontally with respect to the two-dimensional surface. Compared with the loss coefficient αL=52 dB cm−1 for the long-axis direction of the two-dimensional platelet cocrystal, a very large difference of αS=2111 dB cm−1 is present in the crystal short-axis direction. The anisotropic waveguiding ability, αL/αS, is estimated to be 41, which is more than an order of magnitude greater than previously reported two-dimensional platelet crystal waveguides. This supramolecular synthon provides an approach to designing anisotropic photon transporters and highly regulated optical logic circuits.