Easily accessible axial chiral binaphthalene-triarylborane dyes displaying intense circularly polarized luminescence both in solution and in solid-state

Dyes and Pigments 175 (2020) 108168

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Easily accessible axial chiral binaphthalene-triarylborane dyes displaying intense circularly polarized luminescence both in solution and in solid-state Zhiyong Jiang a, b, Tingting Gao a, b, Houting Liu c, Mazen S.S. Shaibani a, Zhipeng Liu a, * a

College of Materials Science and Engineering, Nanjing Forestry University, 159 Longpan Road, Xuanwu District, Nanjing, 210037, China Key Laboratory of Flexible Electronics, Institute of Advanced Materials, Nanjing Tech University (NanjingTech), Nanjing, 211816, China c School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng, 25000, China b

A R T I C L E I N F O

A B S T R A C T

Keywords: Circularly polarized luminescent materials Binaphthalene Triarylborane Chiroptical properties Sensor

The development of small organic CPL-active molecules with large luminescent dissymmetry factors and high quantum yields is highly demanded due to their promising applications in chiroptical devices and sensors. In this paper, we report the synthesis and the chiral optical properties of a series of axial chiral triarylborane dyes. These dyes were facile synthesized by direct borylation of commercially available enantiopure binaphthalenes, and display intense CPL with moderate luminescent dissymmetry factors and high quantum yields in both solution and solid-state, which enable them as efficient CPL emitters. Moreover, fluoride-controlled fluorescence and CPL signals of these dyes were realized, demonstrating their potential application as CPL sensors.

1. Introduction Circularly polarized luminescence (CPL) [1] has been attracting attention in the scientific community owing to their potential utility in three-dimensional (3D) displaying [2–6], CPL lasers [7], optical data storage [8], as well as chirality sensing [9–12]. So far, the CPL active systems are mainly based on chiral metal complexes, organic helical polymers, and nano-assemblies [13–21]. Recently, small organic CPL-active molecules (CPL-SOMs) are generally accepted, mainly due to their easy derivatization, the well-defined backbone modification, and finely tunable emission wavelength [22–24]. Although numbers of CPL-SOMs based on various fluorophores such as dipyrromethene complexes [25–27], pyrene [28], 1,8-naphthalimide [29], helicenes [30–32], quinolone [33], chrysenylenes [34], ortho-oligo phenylene ethynylenes [35] and binaphthyl derivatives [36–42] have been suc­ cessfully developed, the development of CPL-SOMs remains an indis­ putable challenge work due to the following reasons: (1) most of CPL-SOMs display low luminescent dissymmetry factors (glum) values in the range of 10 4–10 2, which is smaller than those observed in su­ pramolecular assemblies and lanthanide complexes (10 2–1.38); (2) rare examples of CPL-SOMs exhibit high quantum yield (Φf) both in solution and in aggregation-state which been reported not only because of the poor fluorescent nature of the fluorophores such as helicene and binaphthalenes but also due to the aggregation-caused emission

quenching effect [43]; (3) complicated synthetic routes or cost­ –ineffectiveness enantiomeric separation through high-performance liquid chromatography (HPLC) are usually needed to obtain enantio­ pure CPL-SOMs. The above disadvantages significantly limit the prac­ tical applications of CPL-SOMs. As a result, the development of CPL-SOMs with the facile synthetic route, purification method, large glum, and high Φf both in solution and in aggregation-state is highly required. Three-coordinate organoboron materials have shown promising ap­ plications in the field of organic light-emitting diodes (OLEDs), nonlinear optical materials, and sensing materials for anions due to their excellent photophysical properties such as high Φf and tunable lumi­ nescent wavelength both in solution and in solid-state [44,45]. By integrating the three-coordinate organoboron unit into to the chiral platform, CPL-SOMs with intriguing CPL properties are to be antici­ pated. However, few examples of organoboron-based CPL-SOMs have been reported [32,46–49]. Although these CPL-SOMs exhibit intriguing CPL properties such as moderate |glum| (0.25–4.2 � 10 3), highly solid-state emission (Φf ¼ 14–53%), complicated synthetic routes, and highly cost enantiomeric separation are still required to obtain these enantiopure triarylborane dyes. Herein, we report a series of easily accessible axial chiral triarylborane dyes as efficient CPL emitters (Fig. 1). By direct borylation of commercially available enantiopure binaphthalenes, these dyes were facile synthesized in a gram scale with

* Corresponding author. E-mail address: [email protected] (Z. Liu). https://doi.org/10.1016/j.dyepig.2019.108168 Received 30 October 2019; Received in revised form 20 December 2019; Accepted 20 December 2019 Available online 23 December 2019 0143-7208/© 2019 Elsevier Ltd. All rights reserved.

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high optical purity. Moreover, these dyes show efficient CPL with moderate |glum| values and high Φf both in solution and solid-state. Furthermore, the potential application of these dyes as a CPL sensor for fluoride anion was also achieved.

In tetrahydrofuran (THF), (R)-/(S)-BM1, and (R)-/(S)-BM2 display almost similar absorption spectra with their absorption maxima (λabs) at 322 nm (log ε ¼ 4.45) for (R)-/(S)-BM1 and 316 nm (log ε ¼ 4.56) for (R)-/(S)-BM2, which can be assigned to the π π* transition bands (Fig. 3). (R)-/(S)-BM1 and (R)-/(S)-BM2 are found to possess a highly blue fluorescence with emission maximum (λem) around 450 nm. The decay lifetime (τ) and Φf are determined to be 8.7 ns and 67% for (R)-/ (S)-BM1 and 7.7 ns and 57% for (R)-/(S)-BM2, respectively (Fig. S7). (R)-/(S)-BM1 and (R)-/(S)-BM2 shows a large Stokes shifts in the range of 9077–9423 cm 1, which are comparable with those of the reported triarylborane dyes [46,54,55]. Moreover, the solvent effects on the ab­ sorption and emission of (R)-/(S)-BM1 and (R)-/(S)-BM2 were exam­ ined (Figs. S5–6). The λabs and λem are hardly affected by the solvent polarity; such polarity-independent behavior also suggests the weak intramolecular charge transfer (CT) effects.

2. Results and discussion 2.1. Design and synthesis Commercially available and optically pure binaphthalene de­ rivatives, with 1,10 -binaphthol as an example, are a family of C2 sym­ metric compounds, that have been wildly employed as an effective chiral source for CPL materials. For example, Cheng and co-works have successfully developed binaphthalene-based CPL-SOMs through chiral perturb strategy [26]. Moreover, it has been reported that the glum values of binaphthalene-based CPL-SOMs could be efficiently tuned by incor­ porating different steric substitutions into binaphthalene [36,50]. On the other hand, dimesitylboryl (B(Mes)2) group, as a bulky substitute with a great steric bulk effect, is generally employed as a key scaffold for the construction of high solid-state emissive boron-containing materials [46,51,52]. In this context, incorporation of B(Mes)2 group into binaphthalene-framework could be helpful to achieve binaphthalene-B (Mes)2 dyes with high glum values and Φf both in solution and solid-state. Scheme 1 shows the synthesis of (R)-/(S)-BM1 and (R)-/(S)-BM2. Compounds (R)-/(S)-1, (R)-/(S)-2, and (R)-/(S)-3 were obtained following a literature procedure [53]. (R)-/(S)-BM1 and (R)-/(S)-BM2 were prepared in a gram scale via borylation of the corresponding iodide precursors, 2 and 3. The chemical structures of these compounds were confirmed by 1H, 13C, 11B NMR, and HRMS (ESI).

2.4. Chiroptical properties in solution The chiroptical features of (R)-/(S)-BM1 and (R)-/(S)-BM2 were investigated by circular dichroism (CD) and CPL spectroscopy in THF (Fig. 3, S8, S9 and Table S8). The CD spectrum of (R)-BM1 shows a small positive Cotton effect at 368 nm followed by a small negative, as well as, a large positive Cotton effect at 333 and 270 nm, respectively. As ex­ pected, mirror-image CD spectra are observed for (S)-BM1. The dissymmetry factors determined for absorption (gabs) at 368 nm are approximately 2.9 � 10 5 for (R)-BM1 and -2.3 � 10 5 for (S)-BM1, respectively. (R)-/(S)-BM2 exhibit more intense and slightly blueshifted CD spectra in comparison with (R)-/(S)-BM1, which is consis­ tent with the results obtained in the UV–Vis spectra. The gabs values at 368 nm are determined to be 1.2 � 10 3 for (R)-BM2 and 1.3 � 10 3 for (S)-BM2. Mirror-image CPL signals for (R)-/(S)-BM1 and (R)-/(S)-BM2 are also observed in the CPL spectra. (R)-BM1 and (S)-BM1 display positive and negative CPL signals at 462 nm. The glum values at maximum emission are 2.2 � 10 3 for (R)-BM1 and 1.7 � 10 3 for (S)-BM1. In comparison with BM1, (R)-/(S)-BM2 exhibits a more intense CPL signal at 458 nm with relatively large glum values ( 5.5 � 10 3 for (R)-BM2 and 6.0 � 10 3 for (S)-BM2). Moreover, the glum values of (R)-/(S)-BM2 are larger than those of binaphthalene-triarylborane dyes reported by Zhao et al. (0.25–1.53 � 10 3) [47], suggesting that incorporating of B (Mes)2 groups into the binaphthalene framework at 3,30 -positions are more effective to achieve large glum values than at 6,60 -positions. To investigate the origin of the difference chiroptical properties be­ tween (R)-/(S)-BM1 and (R)-/(S)-BM2, TD-DFT calculations were per­ formed at the PBE1PBE/6-31G(d) level of theory on the ground (S0) and excited states (S1) of the optimized structures. The g values were esti­ mated based on the following equation: g ¼ 4R/D ¼ 4(|μ|⋅|m|⋅cosθμ,m)/ (|μ|2þ|m|2), where R and D refers to the rotational and dipole strengths,

2.2. Single crystal X-ray structure The molecular structures of (R)- and (S)-BM1 were determined by Xray crystallographic analysis, and related crystallographic data are summarized in Tables S1–3. As shown in Fig. 2 and S1-2, one common feature is that the binaphthyl units show a highly twisted structure. The torsion angles of ∠C(1)-C(2)-C(3)-C(4) and ∠C(41)-C(42)-C(43)-C(44) for each independent molecular in the cell are 91.1 and 75.7� for (R)BM1, and 91.8 and 75.5� for (S)-BM1, respectively. Due to the efficient steric effect of B(Mes)2 group, none of the π π stacking interactions are observed in the packing diagram of (R)-/(S)-BM1, molecules are con­ nected through weak C–H⋅⋅⋅π interactions (Figs. S3–4). 2.3. Photophysical properties The UV–Vis absorption and fluorescence spectra of (R)-/(S)-BM1 and (R)-/(S)-BM2 were measured in various solvents and in solid-state. The photophysical data are summarized in Table 1 (Figs. S5–7, Tables S4–7).

Fig. 1. Chemical structures of (R)-/(S)-BM1 and (R)-/(S)-BM2. 2

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Scheme 1. Synthesis of (R)-/(S)-BM1 and (R)-/(S)-BM2.

Fig. 2. Crystal structures of (R)-BM1 and (S)-BM1 (H-atoms are omitted for clarity).

μ and m demonstrate the relevant electric and magnetic transition dipole moments, respectively, and θμ,m is the angle of vectors between the μ and

m [34,56]. As shown in Table S9, the introduction of two B(Mes)2 groups into the binaphthalene framework at 3,30 -positions effectively increased the |R| values of (R)-/(S)-BM2 in comparison with those obtained in (R)-/(S)-BM1. As a result, (R)-/(S)-BM2 show relative higher |gabs| and | glum| values than those obtained in (R)-/(S)-BM1. This trend is in good agreement with the experimental results, indicating the validity of the theoretical predictions.

Fig. 3. Absorption and normalized emission spectra of (R)-/(S)-BM1 and (R)-/ (S)-BM2 in THF (1.0 � 10 5 mol L 1); the CD and CPL spectra of (R)-/(S)-BM1 and (R)-/(S)-BM2 (2.0 � 10 5 mol L 1 for CD spectra and 5.0 � 10 5 mol L 1 for CPL spectra in THF, respectively).

2.5. Chiroptical properties in the solid state In the fluorescence spectra obtained from powder-state (Fig. 4a), (R)-/(S)-BM1 and (R)-/(S)-BM2 show intense fluorescence at λem ¼ 452 nm (Φf ¼ 30%, τ ¼ 9.8 ns) for (R)-/(S)-BM1 and λem ¼ 446 nm (Φf ¼ 20%, τ ¼ 7.4 ns) for (R)-/(S)-BM2, which are comparable to those observed in THF solution. These results suggest that the intermolecular interactions of (R)-/(S)-BM1 and (R)-/(S)-BM2 are efficiently sup­ pressed due to the large steric effects of B(Mes)2 group and the highly twisted packing structure in solid-state. (R)-/(S)-BM1 and (R)-/(S)-BM2 also exhibit intense CPL signals in their power-state (Fig. 4b). The glum values are determined to be |1.7 � 10 3| for (R)-/(S)-BM1 at 452 nm and |1.0 � 10 3| for (R)-/(S)-BM2 at 446 nm. These results demonstrate the potential use of these dyes in CPL emitters even in solid-state. 2.6. Electrochemical properties Fig. 4. The fluorescence (a) and CPL (b) spectra of (R)-/(S)-BM1 and (R)-/(S)BM2 in the powder-state. Cyclic voltammograms recorded for compounds BM1 (c), BM2 (d) in DCM (scan rate ¼ 20 mV/s).

The electrochemical behaviors of (R)-/(S)-BM1 and (R)-/(S)-BM2 were examined by cyclic voltammetry (CV) (Fig. 4c and d). All potential data of (R)-/(S)-BM1 and (R)-/(S)-BM2 are summarized in Table S10. Table 1 Photophysical data of (R)-/(S)-BM1 and (R)-/(S)-BM2 in solution and in solid-state. Compound

λabs (nm)a

log εa

λem (nm)a

(Φf)a b (%)

τ (ns)

SS(cm

(R)-BM1 (S)-BM1 (R)-BM2 (S)-BM2

322 322 316 316

4.45 4.45 4.56 4.56

455 455 450 450

67 67 57 57

8.70 8.73 7.71 7.73

9077 9077 9423 9423

a b c d

Measured at a concentration of 1.0 � 10 5 mol L 1 in THF at 25 � C. Determined by using 9,10-diphenylanthracene (Φf ¼ 0.93 in cyclohexane) for (R)-/(S)-BM1-2 as reference. Energy gap between the absorption and emission maxima. Absolute quantum yields determined by calibrated integrating sphere systems. 3

1 c

)

λem (nm)

Φfd

τ (ns)

452 452 446 447

31 30 20 18

9.88 9.76 7.36 7.48

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(R)-/(S)-BM1 and (R)-/(S)-BM2 have a similar irreversible oxidative peak and the highest occupied molecule orbital (HOMO) levels are calculated as 5.60 eV and 5.73 eV for (R)-/(S)-BM1 and (R)-/(S)BM2, respectively. The lowest unoccupied molecule orbital (LUMO) energy for these compounds is calculated according to ELUMO ¼ EHOMO þ Bandgap relationship, where Bandgap is the optical band gap energy, calculated based on UV–Vis absorption. The calculated LUMO levels of (R)-/(S)-BM1 and (R)-/(S)-BM2 are around 2.46–2.56 eV, attributable to the reduction of the three-coordinate boron center. 2.7. Utility as CPL sensor for fluoride Fluorescent sensing of fluoride (F ) has received considerable attention due to its high toxicity to the human body [57]. The coordi­ nation of F with boron center of triarylborane dyes would efficiently inhibit the p-π* conjugation of these dyes, resulting in remarkable changes in UV–Vis absorption and fluorescence spectra, which make triarylborane dyes be successfully employed as fluorescent F sensors [58,59]. Therefore, the potential application of (R)-/(S)-BM1 and (R)-/(S)-BM2 as fluorescence and CPL sensor for F was investigated. After adding F to the THF solution of (R)-/(S)-BM1 and (R)-/(S)-BM2, the absorption bands ranging from 250 to 400 nm are linearly decreased with the increment of the concentration of F ([F ]), indicating the coordination of F with the boron center (Fig. 5, S10-S11). In the CD spectra, the Cotton effect of the intensity at 360, 330, and 270 nm are distinctly decreased, resulting in the disappearance of the Cotton effect around 360 nm, and the emergence of a broad Cotton effect ranging from 270 to 380 nm. In the fluorescent titration diagrams (Fig. 6a and b), (R)-/(S)-BM1 and (R)-/(S)-BM2 show drastically fluorescence intensity decrement (6.2-fold for (R)-BM1), accompanied by the appearance of new emission bands at 405 nm for (R)-/(S)-BM1 and 364 nm for (R)-/(S)-BM2, after the addition of F . These ratiometric changes become saturated when [F ] reaches 1.0 and 3.0 equiv for (R)-/(S)-BM1 and (R)-/(S)-BM2, respectively. The emission band at 364 nm should be ascribed to the emission of [naphthalene-B(Mes)2F]- complex, while the broad emission band at 405 nm should contain both the emission of the naphthalene and the [naphthalene-B(Mes)2F]-. Therefore, a more hypsochromic shift of (R)-/(S)-BM2 than that of (R)-/(S)-BM1 is well explained. Ratiometric responses of (R)-/(S)-BM1 and (R)-/(S)-BM2 towards F were also observed in CPL spectra (Fig. 6c and d). CPL signals at 467 nm for (R)BM1 and (S)-BM1 are decreased and blue-shifted to 430 nm with the

Fig. 6. The fluorescent titration diagram of (R)-BM1 (a) and (S)-BM2 (b) by nBu4NF (1.0 � 10 5 mol L 1). The CPL titration diagram of BM1 (c), BM2 (d) by n-Bu4NF (5.0 � 10 5 mol L 1).

[F ] reaching 1.2 from 0 equiv. (R)-/(S)-BM2 shows almost totally a quenched CPL signal at 456 nm when [F ] reaches 1.6 equiv. Different from the distinct fluorescence intensity enhancement at 364 nm, the increment of CPL signals around 360 nm is very small, suggesting that the coordination of F with boron center greatly influenced the chirality of (R)-/(S)-BM2 in excited states. The distinct CPL variation can be well explained by TD-DFT calculations (Table S9). After coordinating with F , the |R| values of [(R)-/(S)-BM1-F]- and [(R)-/(S)-BM2-2F]2- are significantly decreased in comparison with those of (R)-/(S)-BM1 and (R)-/(S)-BM2. As a result, smaller |gabs| and |glum| values of the fluoridecomplexes are obtained than those of (R)-/(S)-BM1 and (R)-/(S)-BM2. 3. Conclusions In summary, we presented a simplified, accessible synthetic way to provide axial chiral triaryborane dyes ((R)-/(S)-BM1 and (R)-/(S)-BM2) via direct borylation of commercially available enantiopure binaph­ thalenes. The incorporation of B(Mes)2 group to the binaphthalene framework results in highly fluorescence quantum yield and intense CPL both in solution and in solid-state. In THF solution, (R)-/(S)-BM1 and (R)-/(S)-BM2 display intense blue fluorescence with high Φf in the range of 57–67%. (R)-/(S)-BM1 and (R)-/(S)-BM2 also exhibit CPL signals with good |glum| values ranging from 1.7 � 10 3 to 6.0 � 10 3. No distinct emission and CPL quenching are observed for (R)-/(S)-BM1 and (R)-/(S)-BM2 in powder-state. The Φf (18–31%) and |glum| values (1.0–1.7 � 10 3) were comparable with those observed in solution. Furthermore, (R)-/(S)-BM1 and (R)-/(S)-BM2 exhibit ratiometric fluo­ rescence and CPL signal response towards F , demonstrating their promising application as CPL sensors. 4. Experimental section 4.1. Methods and materials Solvents in the experiment were dried prior to the usage by common methods in organometallic chemistry. Chemicals were commercially obtained and used as received. All reactions of air-sensitive compounds were preceded under the protection of the inert gases by using Schlenk techniques. Flash column chromatography was carried out using silica gel bought from Liangchen Guiyuan materials Co. The 1H and 13C NMR spectra were recorded on a Bruker AV-300 spectrometer with 300 MHz for 1H NMR and 75 MHz for 13C NMR. 11B NMR spectra were acquired with quartz NMR tubes, and the spectra were then referenced externally

Fig. 5. The absorbance titration diagram of (R)-BM1 (a) and (R)-BM2 (b) by nBu4NF (1.0 � 10 5 mol L 1). The CD titration diagram of BM1 (c), BM2 (d) by n-Bu4NF (2.0 � 10 5 mol L 1). 4

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to BF3⋅Et2O (δ ¼ 0). Chemical shifts are presented in ppm relative to Si (CH3)4 (1H). 1H NMR coupling constants (J) are reported in Hertz (Hz), and multiplicity is indicated as follows: s (singlet), d (doublet), m (multiplet). Mass spectra were collected on an LCQ (ESI-MS, Thermo Finnigan) mass spectrometer.

Circularly polarized luminescence (CPL) spectra in THF solution for (R)-/(S)-BM1-2 were recorded with a JASCO CPL-300 spectro­ fluoropolarimeter at room temperature. (λex ¼ 290 nm, cell length: 10 mm, bandwidth: 1 nm, scanning speed: 200 nm/min, data pitch: 1 nm, accumulations: 6).

4.2. Synthesis

4.4. Electrochemical analyzer

Compounds (R)-/(S)-1-3 were obtained following a literature pro­ cedure [53].

Cyclic voltammetry was measured on the CHI 660B electrochemical analyzer in dried and degassed DCM solutions under an N2 atmosphere containing n-Bu4NPF6 as the supporting electrolyte with a scan rate of 20 mV/s. The CV cell consisted of a Pt wire counter electrode, an Ag/ AgCl reference electrode, and a glassy carbon electrode. The HOMO and LUMO energy levels were calculated using the first anodic peak poten­ tial (Epa) according to the equations EHOMO ¼ (Epa þ 4.8) eV and ELUMO ¼ EHOMOþ Bandgap eV, respectively.

4.2.1. Synthesis of (R)-/(S)-BM1 To a solution of (R)-2 or (S)-2 (2.0 g, 4.56 mmol) in dry THF (50 mL) was added n-BuLi (4.28 mL, 1.6 M in hexane, 6.84 mmol) dropwise by syringe at 78 � C under N2. The mixture was stirred for 1 h at the same temperature. Then a solution of dimesitylboron fluoride (2.44 g, 9.12 mmol) in dry THF (45 mL) was added to the reaction mixture. The re­ action mixture was allowed to warm to room temperature and stirred for 6 h. The reaction was quenched with saturated NH4Cl solution, and the aqueous layer was extracted with dichloromethane. The combined organic layer was washed with water, dried over anhydrous MgSO4, filtered, and concentrated under reduced pressure. The solvent was removed and purified by a silica gel column chromatography (petroleum ether: dichloromethane ¼ 3: 1, Rf ¼ 0.30) to give pure product as white solids. 60 (c 0.01, (R)-BM1 (0.9 g. 45%), m.p. 199–201 � C, [α]25 D ¼ acetone); (S)-BM1 (1.04 g. 52%), m.p. 198–199 � C, [α]25 D ¼ 30 (c 0.01, acetone). 1H NMR (300 MHz, CDCl3) δ/ppm ¼ 7.94 (d, J ¼ 9.0 Hz, 1H), 7.87–7.81 (m, 3H), 7.42 (d, J ¼ 9.0 Hz, 1H), 7.31 (d, J ¼ 9.0 Hz, 2H), 7.27–7.18 (m, 3H), 7.12 (d, J ¼ 9.0 Hz, 1H), 6.78 (s, 4H), 3.77 (s, 3H), 2.78 (s, 3H), 2.28 (s, 6H), 2.12 (s, 12H). 13C NMR (75 MHz, CDCl3) δ/ppm ¼ 159.1, 154.5, 142.5, 142.3, 140.2, 138.1, 136.1, 135.8, 133.6, 130.1, 129.0, 128.8, 128.7, 127.7, 127.4, 126.7, 126.0, 124.9, 124.8, 123.7, 123.0, 122.7, 119.4, 113.4, 60.3, 56.0, 22.7, 20.8. 11B NMR (192 MHz, CDCl3) δ/ppm ¼ 71.4. HRMS (ESIþ): calcd. for C40H39BO2Na: [MþNa]þ ¼ 585.2941, found: [MþNa]þ ¼ 585.2952.

Author statement Zhiyong Jiang: Conceptualization, Methodology, Investigation, Writing-Original draft preparation. Tingting Gao: Investigation, Meth­ odology, Data curation, Validation. Houting Liu: Visualization, Inves­ tigation. Mazen S.S. Shaibani: Investigation, Writing - Review & Editing. Zhipeng Liu: Conceptualization, Writing - Review & Editing, Project administration, Supervision. Declaration of competing interest We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome. Acknowledgments This work was supported by the National Natural Science Foundation of China (21971115) and Key University Science Research Project of Jiangsu Province (17KJA150004).

4.2.2. Synthesis of (R)-/(S)-BM2 This compound was prepared in the same methods as described for (R)-BM1 using (R)-3 or (S)-3 (2.1 g, 3.6 mmol) n-BuLi (6.9 mL, 1.6 M, 10.8 mmol) and dimesitylfluoroborane (3.87 g, 14.4 mmol). The puri­ fication by a silica gel column (petroleum ether: dichloromethane ¼ 3: 1, Rf ¼ 0.30) afforded pure product as white solids. (R)-BM2 (1.08 g. 51%), m.p. 145–146 � C, [α]25 D ¼ 400 (c 0.01, acetone); (S)-BM2 (1.19 g. 56%), m.p. 137–139 � C, [α]25 420 (c D ¼ 0.01, acetone). 1H NMR (300 MHz, CDCl3) δ/ppm ¼ 7.84 (s, 2H), 7.79 (d, J ¼ 7.5 Hz, 2H), 7.34–7.26 (m, 3H), 7.19–7.24 (m, 3H), 6.76 (s, 8H), 2.77 (s, 6H), 2.26 (s, 12H), 2.07 (s, 24H). 13C NMR (75 MHz, CDCl3) δ/ppm ¼ 159.3, 143.1, 142.9, 140.6, 138.6, 136.8, 136.7, 130.4, 129.3, 128.2, 127.3, 125.6, 124.2, 123.2, 60.57, 23.21, 21.19. 11B NMR (192 MHz, CDCl3) δ/ppm ¼ 72.8. HRMS (ESIþ): calcd. for C58H60B2O2Na: [MþNa]þ ¼ 833.4677, found: [MþNa]þ ¼ 833.4701.

Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.dyepig.2019.108168. References [1] Riehl JP, Richardson FS. Circularly polarized luminescence spectroscopy. Chem Rev 1986;86(1):1–16. [2] Feuillastre S, Pauton M, Gao L, Desmarchelier A, Riives AJ, Prim D, et al. Design and synthesis of new circularly polarized thermally activated delayed fluorescence emitters. J Am Chem Soc 2016;138(12):3990–3. [3] Li M, Li SH, Zhang D, Cai M, Duan L, Fung MK, et al. Stable enantiomers displaying thermally activated delayed fluorescence: efficient oleds with circularly polarized electroluminescence. Angew Chem Int Ed 2018;57(11):2889–93. [4] Song FY, Xu Z, Zhang QS, Zhao Z, Zhang HK, Zhao WJ, et al. Highly efficient circularly polarized electroluminescence from aggregation-induced emission luminogens with amplified chirality and delayed fluorescence. Adv Funct Mater 2018;28(17):1800051. [5] Wang Y, Zhang Y, Hu W, Quan Y, Li Y, Cheng Y. Circularly polarized electroluminescence of thermally activated delayed fluorescence-active chiral binaphthyl-based luminogens. ACS Appl Mater Interfaces 2019;11(29):26165–73. [6] Wu ZG, Han HB, Yan ZP, Luo XF, Wang Y, Zheng YX, et al. Chiral octahydrobinaphthol compound-based thermally activated delayed fluorescence materials for circularly polarized electroluminescence with superior eqe of 32.6% and extremely low efficiency roll-off. Adv Mater 2019;31(28):e1900524. [7] Chen F, Gindre D, Nunzi J-M. Tunable circularly polarized lasing emission in reflection distributed feedback dye lasers. Opt Express 2008;16(21):16746. [8] Wagenknecht C, Li CM, Reingruber A, Bao XH, Goebel A, Chen YA, et al. Experimental demonstration of a heralded entanglement source. Nat Photonics 2010;4(8):549–52. [9] Gong J, Yu M, Wang C, Tan J, Wang S, Zhao S, et al. Reaction-based chiroptical sensing of clo(-) using circularly polarized luminescence via self-assembly organogel. Chem Commun 2019;55(72):10768–71.

4.3. Photophysical properties UV–Vis absorption and fluorescence spectra were recorded on a Shimadzu UV-1750 spectrometer and a FLUOROMAX-4 spectrometer at room temperature, respectively. A solution of the sample in a 1 cm square quarts cell was used for the measurement. The absolute quantum yields (Φf) and fluorescence lifetimes of the powder samples were determined with a Horiba Jobin Yvon Fluorolog-3 spectrofluorimeter under an air atmosphere at room temperature. Fluorescence quantum yield of (R)-/(S)-BM1 and (R)-/(S)-BM2 in solution were determined by using 9,10-diphenylanthracene (Φf ¼ 0.93 in cyclohexane) as reference. Circular dichroism (CD) spectra of all compounds, when dissolved in THF solution, were measured using a JASCO J-820 spectropolarimeter. 5

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