Synthesis of Highly Luminescent Chiral Nanographene

Abstract

Chiral nanographenes with both high fluorescence quantum yields (Φ F ) and large dissymmetry factors (g lum ) are essential to the development of circularly polarized luminescence (CPL) materials. However, most studies have been focused on the improvement of g lum , whereas how to design highly emissive chiral nanographenes is still unclear. In this work, we propose a new design strategy to achieve chiral nanographenes with high Φ F by helical π-extension of strongly luminescent chromophores while maintaining the frontier molecular orbital (FMO) distribution pattern. Chiral nanographene with perylene as the core and two dibenzo[6]helicene fragments as the wings has been synthesized, which exhibits a record high Φ F of 93 % among the reported chiral nanographenes and excellent CPL brightness (B CPL ) of 32 M À 1 cm À 1 .Nanographenes, which are nanoscale (1-100 nm) graphene fragments, have been regarded as promising candidates for next-generation semiconductors. [1] The bottom-up synthesis of nanographenes has enabled precise control over their sizes, topologies, and edge structures, giving rise to various nanographenes with appealing optical, electronic, and magnetic properties. [2] Recently, chiral nanographenes with helical structures have attracted much attention, [3] partly owing to their great potential as circularly polarized luminescence (CPL) materials. [4] The fluorescence quantum yields (Φ F ) and luminescence dissymmetry factors (g lum ) are[*] J.

The Physical Mechanism of Linear and Nonlinear Optical Properties of Nanographene-Induced Chiral Inversion

“…This is consistent with the results of the HOMO-LUMO gap analysis. In the experiment, the maximum absorption values of the lowest energies of the compounds 1-rac and 1-meso are 538 nm and 539 nm, respectively, which is relatively small compared to the maximum absorption values of 545 nm and 546 nm of the lowest energies of 1-rac and 1-meso in the calculation of TD-DFT, reflecting the accuracy of the calculation [ 27 ]. The UV-Vis spectra show that the absorption spectra bands of 1-meso and 1-rac are mainly within 220–700 nm.…”

“…Ji-Kun Li et al experimentally obtained two enantiomers of 1-(P, P) and 1-(M, M) by the chiral separation of 1-rac at room temperature [ 27 ], as shown in Figure S6 . Therefore, we judge the chirality of 1-meso and 1-rac enantiomers by calculating their electron circular dichroism, as shown in Figure 10 .…”

“…proposed a new strategy to extend the helical π of luminous groups with a high diameter to obtain chiral nanographenes with excellent luminous properties while maintaining the distribution of frontier molecular orbitals (FMOs). Using perylene as the parent core, the authors synthesized chiral nanographenes with an content of 93% and separated them by chiral HPLC to obtain 1-meso and 1-rac [ 27 ].…”

Heptagon-Embedded Helicene Derivatives: Synthesis, Crystal Structural Analyses, and Circularly Polarized Luminescence

“…As shown in Figure S8, the racemization barrier of (P)-13 was 30.37 kcal/mol, which was smaller than that of the DFT result. 43,44 The dissymmetry factor of absorbance (g abs ) is calculated to be +4.3 × 10 −3 (307 nm)/−1.3 × 10 −3 (390 nm) for (P)-13 and −5.1 × 10 −3 (307 nm)/+1.5 × 10 −3 (390 nm) for (M)-13, respectively. Upon irradiation, mirror-shaped CPL spectra centered at 503 nm, consistent with its emission maximum, are observed for such enantiomers of 13 (Figure 4a).…”

X-ray and Optical Circular Dichroism as Local and Global Ultrafast Chiral Probes of [12]Helicene Racemization

“…Helicene chemistry is a rapidly growing field − with applications to asymmetric catalysis, nonlinear optics, spin filters, switches and sensors, and the design of molecular machines . They can be synthesized with different sizes and are usually referred to as [ n ]­helicenes, where n denotes the number of benzene rings.…”