Unusual Magnetic Field Responsive Circularly Polarized Luminescence Probes with Highly Emissive Chiral Europium(III) Complexes

Abstract Chirality is ubiquitous within biological systems where many of the roles and functions are still undetermined. Given this, there is a clear need to design and develop sensitive chiral optical probes that can function within a biological setting. Here we report the design and synthesis of magnetically responsive Circularly Polarized Luminescence (CPL) complexes displaying exceptional photophysical properties (quantum yield up to 31 % and |glum| up to 0.240) by introducing chiral substituents onto the macrocyclic scaffolds. Magnetic CPL responses are observed in these chiral EuIII complexes, promoting an exciting development to the field of magneto‐optics. The |glum| of the 5D0 → 7F1 transition increases by 20 % from 0.222 (0 T) to 0.266 (1.4 T) displaying a linear relationship between the Δglum and the magnetic field strength. These EuIII complexes with magnetic CPL responses, provides potential development to be used in CPL imaging applications due to improved sensitivity and resolution.

= Eq. (S1) where is the overall quantum yield, which can be measured; is the actual lifetime of the emitting excited state and is the radiative lifetime without any non-radiative de-activation processes; ,0 is a constant equal to 14.65 s -1 ; is the refractive index of the using solvent; and are the integrated intensities of the total 5 D 0 → 7 F J transitions and the integrated intensity of magnetic dipole transition ( 5 D 0 → 7 F 1 ) respectively.
The number of water molecules coordinated to the first coordination sphere of Eu(III) metal center (q value) was determined according to equations published by Parker et al. [3] and Horrocks et al. [4] : Parker's equation: where is a constant equal to 1.2 ms -1 for europium; − is the lifetime measured in water and − is the lifetime measured in deuterated water; is the number of carbonyl-bound amide NH oscillators with Eu.
Horrocks' equations: where , , , , and are constants equal to 1. Titration conditions. pH titrations were performed by adjusting the pH using 1 M NaOH and 1 M HCl solution.
Anion titrations were performed by adding the stock solution of anion mixture included 45Mm of Na 2 HPO 4 ,5M of NaCl, 115mM of sodium lactate, 6.5Mm of sodium citrate and 0.75M of NaHCO 3 from 0µL to 120µL into 3mL aqueous solution of Eu(III) complexes.
CPL measurements. Samples were dissolved in 0.1 M HEPES, MeOH and DMSO (HPLC grade from Sigma-Aldrich) with UV absorbance at around 0.5. Excitation wavelength at 340 nm was used. 180° sample geometry with unpolarized excitation light, the distance between sample and detector were adjusted for maximum signal intensity. [5] In magnetic studies, bundled magnet components were placed into the sample chamber from 0.2 to

T in the direction perpendicular to the excitation light beam.
Single Crystal X-ray Diffraction. The crystal data reported in the manuscript was collected on a Bruker D8-Venture Diffractometer System with a micro-focus Mo-Kα radiation. The data was collected at room temperature.
Multi-scan absorption correction was applied by SADABS program, [6] and the SAINT program utilised for the integration of the diffraction profile. [7] The structure was solved by direct method and was refined by a full-matrix least-squares treatment on F 2 using the SHELXLE programme system. [8] The crystallographic data for the structural analyses have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 1991693, and the data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif.

Synthesis of chromophore
Scheme S1. Synthesis of the chromophore compound, 6.
The chromophore was synthesized according to the literature [9] with some minor modifications. NMM (10.3 g, 102 mmol) was added into a mixture of 4-ethynylaniline (6 g, 51 mmol) and 4-methoxy-4oxobutanoic acid (8.8 g, 67 mmol) in THF (50 mL), then the reaction mixture was cooled to 0 -10 °C with ice/water bath. HATU (25 g, 66 mmol) was added slowly, then after reacting for 16 h, concentrated and the residue was poured into 300 mL of water, the precipitate was filtered and washed with water, the filter cake was dried in oven, this resulted in the product 4 as a light yellow solid (9.5 g, 80% yield). 1  The mixture of compound 4 (2 g) and the compound 3 (2.5 g) in THF (20 mL) and DIPEA (4 mL) was degassed three times. Then added dppf(PdCl 2 ) (0.26 g) and CuI (120 mg), temperature was increased to 70 o C and the mixture was reacting at this temperature for 16 h. Then concentrated and the residue was purified by column chromatography (silica) with CHCl 3 and ethanol (50:1 to 20:1), this resulted in the product as a light yellow solid (compound 5) (2.09 g, yield 65%). 1  DIPEA (2 g, 15.5 mmol) was added to the solution of compound 5 (2 g, 5 mmol) in dichloromethane (20 mL), the solution was cooled to 0 -10°C and methanesulfonyl chloride (1.2 g, 10 mmol) was added. After reacting for 20 mins, the solution was quenched by added 10 mL of water. The organic and aqueous layers were separated and the organic layer was washed with 10 mL water and 10 mL saturated NaCl solution, dried with magnesium sulfate. The solid was filtered and the filtrate was concentrated. Compound 6 (2 g, yield 83%) was used to the next step reaction without further purification.
(S)-2-aminopentan-1-ol (20 g) and benzaldehyde (22.6 g) in methanol (60 mg) and dichloromethane (260 mL DIPEA (2 g) was added to a solution of compound 5 (2 g) in dichloromethane (20 mL), the solution was cooled to 0 -10 °C and added methanesulfonyl chloride (1.2 g), after reacting for 30 mins, the solution was quenched by added 10 mL of water, separated the organic and aqueous layers, the organic layer was washed with 10 mL water and 10 mL sat. NaCl solution, dried with magnesium sulfate, filtered and the filtrate was concentrated.
The product of 20 (2 g, yield 83%) was used to the next step reaction without any further purification.
Compound A2 (500 mg) was dissolved in acetonitrile (40 mL), NaHCO 3 (183 mg) was added, followed by adding compound 20 (500 mg) in DMSO (2 mL) and acetonitrile (8 mL) dropwise into the reaction mixture at 50 °C slowly (10 h). Then, reacted for another 8 h. When the solution was cooled down, filtered the solid and the filtrate was concentrated under reduced pressure to give brown oil. This crude product was purified by semi-preparative HPLC and concentrated to get the product as a light yellow oil, B2 (220 mg, yield 17%). 1
Compound (S)A3 (440 mg) was dissolved in acetonitrile (40 mL), NaHCO 3 (130 mg) was added, followed by adding compound 20 (300 mg) in DMSO (2 mL) and acetonitrile (20 mL) dropwise into the reaction mixture at 50 °C slowly (5 h). Then, reacted for another 8 h, the solution was cooled down, filtered and the filtrate was concentrated under reduced pressure to give a brown oil. This crude product was purified by semi-preparative HPLC and concentrated to get the product as a light yellow oil (S)B3 (170 mg, yield 17%). 1

Synthesis of peptoid
Fmoc-protected Rink Amide resin (100-300 mg, 0.1-0.2 mmol, typical loading between 0.6 -0.8 mmol g -1 ) was swollen in DMF (overnight, at RT) in a 20 mL polypropylene syringe fitted with two polyethylene frits. The resin was deprotected with piperidine (20 % in DMF v/v, 2 x 20 min) and washed with DMF (5 x 2 mL). The resin was treated with bromoacetic acid (2 mL, 0.6 M in DMF) and DIC (0.20 mL, 50 % v/v in DMF) for 20 minutes at room temperature at 400 rpm. The resin was washed with DMF (5 x 2 mL), before the desired amine submonomer was added (2 mL, 0.8-2.0 M in DMF) and allowed to react for 60 minutes at room temperature on a block shaker at 400 rpm. The resin was again washed with DMF (5 x 2 mL) and the bromoacetylation and amine displacement steps were repeated until the final submonomer had been added and the desired peptoid sequence had been obtained [12] .
The linear α-peptoid was synthesised via manual SPPS, as described above and the glycine spacer added as follows. The peptoid on resin was swollen in DMF in a polypropylene syringe fitted with a polyethylene frit (overnight, at RT). DIPEA (5 equivalents with respect to the resin) was added to a solution Fmoc-protected glycine (5 equivalents with respect to the resin, dissolved in the minimum amount of DMF) and PyBOP (5 equivalents with respect to the resin in DMF). The DIPEA/PyBOP/glycine solution (2.0 mL) was then added to the resin bound peptoid and left for 1 hour at 25 ˚C on a block shaker at 400 rpm. The resin was washed with DMF (5 x 2 mL) and treated with piperidine (20 % in DMF v/v, 2 x 20 minutes) and then washed with DMF (5 x 2 mL). To prepare the glycine-glycine spacer, the procedure was repeated and a second Fmoc-Gly-OH was added.
A test cleavage of the linear α-peptoid-peptide hybrid Fmoc-Gly-Gly-Npmb-NLys-Npcb-NLys-NH 2 was carried out and LC mass spectroscopy confirmed that the target molecule had been prepared -observed m/z 969.5 = [M + H] +