Tuning the solid-state emission of liquid crystalline nitro-cyanostilbene by halogen bonding

The first example of halogen-bonded fluorescent liquid crystals based on the interaction of iodofluorobenzene derivatives with nitro-cyanostilbenes is reported. The systematic variation of the fluorination degree and pattern indicates the relevance of the halogen bond strength for the induction of liquid crystalline properties. The modular self-assembly approach enables the efficient tuning of the fluorescence behaviour and mesomorphic properties of the assemblies.


Materials and methods
Compounds and solvents were used as obtained from suppliers without further purification. 1 H and 13 C NMR spectra of the intermediates and products were recorded in deuterated solvents (CDCl 3 ,  or MeOD) with a Bruker DRX 300. Mass spectra were obtained with a Bruker amaZon (MS) and IR spectra were recorded with a Varian 3100 FT-IR, Excalibur Series, ATR IR spectrometer. Polarized optical microscopy (POM) images/videos were taken on a Nikon Eclipse Ni equipped with an OptixCam Summit K2 OCS-D3K4-14-52X microscope camera and an LTS420 hotstage from Linkam Scientific Instruments Ltd. The images were recorded by an Imaging Source camera OptixCam K2. DSC thermograms were recorded using a Mettler Toledo DCS3+/700/866/Argon with a heating/cooling speed of 10 °C/min (sample weight ≈5 mg). UV-visible spectroscopy was performed using a Thermo Fisher Evolution 201 spectrophotometer.

Experimental procedures
Scheme S1: The synthetic route for the synthesis of XB-acceptors, XB-donors and supramolecular assemblies.
Synthesis of compound NO 2 -C n (n = 1, 8, 9, 10, 11): The desired compounds were synthesised based on a reported procedure S1 with a small modification. 4-Alkoxybenzaldehyde (1 equiv), CH 3 ONa (1 equiv) and 20 ml ethanol were placed into a 250 ml boiling flask. When the 4-alkoxybenzaldehyde and CH 3 ONa had completely dissolved in ethanol, 4-nitrophenylacetonitrile (1 equiv) was added and the S2 mixture was stirred at 25 °C for 8 h. The final reaction mixture was filtered, the solid products were collected and washed several times with ethanol to obtain the yellow green solid products with a yield of 60-65%.

Synthesis of the complexes NO
CH 2 Cl 2 solutions of compound NO 2 -C n and compound F 4 St/F 4 Az S2,S3 were mixed in a 1:1 molar ratio. The solvent was allowed to evaporate overnight followed by subsequent drying under vacuum to give an orange solid.     Figure S13: DSC traces obtained from the 2 nd heating and 2 nd cooling cycle at a rate of 10 °C min −1 for compound NO2-C9.
Heating Cooling S11 Figure S14: DSC traces obtained from the 2 nd heating and 2 nd cooling cycle at a rate of 10 °C min −1 for compound NO2-C10.
Figure S15: DSC traces obtained from the 2 nd heating and 2 nd cooling cycle at a rate of 10 °C min −1 for compound NO2-C11.

Heating
Cooling Heating Cooling S12 Figure S16: DSC traces obtained from the 2 nd heating and 2 nd cooling cycle at a rate of 10 °C min −1 for compound NO2-C8•••F4St.     Computational studies:

Theoretical specifications:
Structures of all complexes were optimised with the Gaussian 09 packages. The interaction energies were obtained as the energy differences counterpoise correction on the mp2/LanL2DZ. The basis set super position error (BSSE) has been undertaken for achieving errorless data of the supramolecule [S4,S5] .
Imaginary modes were minimised using the screwing method. In this method, the optimised geometry is resubmitted upon manual displacement of the second frequency. During the second job submission, the command Opt = tight was used.