3D Boranil Complexes with Aggregation-Amplified Circularly Polarized Luminescence

Abstract

The development of small organic CPL-active molecules with large luminescent dissymmetry factors is highly demanded due to their promising applications in chiroptical devices and sensors. This work describes the design and synthesis of a new family of CPL-active BF2 complexes, (R p)/(S p)-3a–3e, which were constructed by fusing a N̂O-chelated BF2 complex with [2.2]­paracyclophane. These complexes display aggregation-amplified CPL with moderate dissymmetry factors values and moderate quantum yields both in solution and in the solid state. In addition, these photophysical properties were rationalized via X-ray diffraction and TD-DFT calculations.

Synthesis, structural characterization, and chiroptical properties of planarly and axially chiral boranils

“…Interestingly, chiral boranils are known to exhibit circularly polarized fluorescence, which makes them appealing for incorporation into OLEDs as circularly polarized electroluminescent materials. [20][21][22][23][24] Satisfyingly, the enantiomers 8b,d and 9b-d revealed almost mirrorimage CPL activity (Figure 10). Regarding the dissymmetry factors, which reflect the percentage of circularly polarized emitted light (g lum = 2(I L À I R )/(I L + I R )), the values ranged from 1 Â 10 À4 to 1 Â 10 À3 , with positive signals for the (+) enantiomers (and vice versa) and with the highest value being found for 9b (see Table 1).…”

“…The boranil part displays classical metrics, with O B and B N bond lengths of 1.445 and 1.590 Å, respectively, which are in the range of similar four-coordinate boron(III) derivatives. [21][22][23][24] The PCP unit also shows classical features, with phenyl rings that are almost planar (maximum dihedral angle of 14.92 ) and parallel to each other (centroid-centroid distance of 2.978 Å and dihedral angles of CH 2 CH 2 bridges as low as À13.49 and 7.49 ). Interestingly, the PCP and the boranil parts are linked through an N C single bond (with a length of 1.456 Å), which displays axial chirality due to a B N C 1 C 2 dihedral angle of À76.10 , thus representing the R a configuration associated with the S p stereochemistry of the PCP fragment.…”

“…20 Lastly, while this work was in progress, organoboranes 6a-i and 7 combining one or two BF 2 moieties directly with the benzene rings of an (R p )-/(S p )-[2.2]paracyclophane (PCP) unit have been designed and their aggregation-amplified CPL emission has been studied, demonstrating fluorescence dissymmetry factors jg lum j up to 7.6 Â 10 À3 in tetrahydrofuran (THF)/water solution. [21][22][23][24] Although such systems may appear as potential candidates for CPL applications, they often require multistep synthesis that makes structural variations difficult and time-consuming, which strongly influences the cost of F I G U R E 1 Chemical structures of selected known circularly polarized luminescence-active chiral boranils (for clarity, a single enantiomer is presented in each case). the final material.…”

Aggregation‐Induced Emission and Circularly Polarized Luminescence Duality in Tetracationic Binaphthyl‐Based Cyclophanes

“… [22] succeeded in the immobilization of the propeller‐like conformation of TPE displaying AIE and CPL spectra in the aggregated state. In addition, Duan and Gong [23] reported a planar chiral boranyl‐based [2.2]paracyclophane, which shows an amplified CPL emission upon aggregation.…”

Aggregation‐Induced Emission and Circularly Polarized Luminescence Duality in Tetracationic Binaphthyl‐Based Cyclophanes

“…In 2016, Zheng et al [22] succeeded in the immobilization of the propeller-like conformation of TPE displaying AIE and CPL spectra in the aggregated state. In addition, Duan and Gong [23] reported a planar chiral boranyl-based [2.2]paracyclophane, which shows an amplified CPL emission upon aggregation.…”