Symmetry Breaking and Chiral Side Group Strategy to Manipulate Circularly Polarized Luminescence

Abstract

Symmetry breaking occasionally occurs during crystallization of organic compounds, which however has seldom been utilized to fabricate supramolecular helices and chiroptical materials with circularly polarized luminescence (CPL). Here, we present a symmetry breaking protocol to build achiral aromatic phenols into supramolecular helices with chiroptical activities. Statistic results from the Cambridge Structural Database (CSD) indicate that the symmetry breaking of phenol crystals generically occurs. This strategy potentially shall provide versatile crystalline materials toward chiroptical applications, which unfortunately are majorly ignored. In the phenol crystal, the zigzag hydrogen bonds between hydroxyl groups enable one-dimensional helical arrangement, showing tunable CPL depending on the extended fused rings. The symmetry breaking strategy is convenient and cost-effective, which however is unpredictable and serendipitously occurs with hetero-chirality. To address this issue, chiral cholesteryl side group was introduced to afford helical structures with homo-chirality, which also illustrates the substitute-position determined chirality. Cholesteryl positions at 1′- and 2′-naphthalene produced M- and P-handed helices with left and right CPL, respectively, which applies for the analogues like naphthylamine. Cholesteryl conjugation strategy compensates the nondeterminacy in symmetry breaking, rationalizing the molecular design for organic chiroptical materials.