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 costeffective, 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.

Highly Efficient Wavelength‐Tunable Circularly Polarized Luminescence Film Constructed by Responsive Chiral Aggregation‐induced Emission Luminophore

“…Circularly polarized luminescence (CPL) has gained enormous interest due to its charming properties for reflecting chiral information in excited states, [1][2][3] showing promising application prospects in chiral optoelectronics, 3D optical displays, information security encryption et al [4][5][6][7][8][9][10][11][12][13] Organic CPL materials with inherent benefits including structural regulation, easy availability, and high quantum efficiency show limitless possibilities in the optical application. [14][15][16][17][18] Aggregation-induced emission (AIE) compounds with high luminescence quantum yield (Φ F's ) in the solid state are superior to typical organic compounds for preparing CPL materials, which can produce effective photoluminescence without aggregation-caused quenching (ACQ) during the assembly process. [19][20][21] Especially, AIE-active molecule is employed for supramolecular self-assembly, which can dramatically increase the luminescence asymmetry factor (g lum ) of the CPL materials.…”

Phosphorescent Thermal Chiroptical Switch Built through Highly Efficient Chiral Recognition and Amplification

“…Formation of enantiorich or pure aggregates is reinforced by the crystallization-induced chiral amplification with chiral source from inherent molecular chirality, external fields, or in spontaneous way. − Materials that could undergo spontaneous formation or solution during crystallization in racemates are defined as conglomerate crystals, which have been recognized as a widely existing behavior. − Conglomerate crystallization phenomenon contains the processes of both symmetry breaking and chiral amplification. − Though chemists are familiar with this phenomenon, its potentials in asymmetric synthesis and especially functional chiroptical materials are underdeveloped and rarely recognized. Statistic data from Cambridge Structural Database suggest that about 10% crystals have conglomerate behaviors, which potentially is an enormous candidate library for diversified chiroptical usages. − The state-of-art exploration with respect to chiroptical materials is, however, pretty rare. , …”

“…One needs to overcome the random resolution into opposite-handed crystals, which empirically requires the external chiral perturbation such as circularly polarized light or molecular chiral seeds that trigger or control the chiral amplification into enantioenriched materials. , The introduction of molecular chiral seeds that directs the enantiobais should consider the interaction and recognition between the two species. − Strong binding affinity and efficient chiral recognition facilitate sergeant-and-soldier’s rule as well as the generation of materials with excellent optical activity, while the screening of efficient chiral seeds is challenging due to the poor understanding of structural–property correlations. − …”