Design, Synthesis, Characterisation and Host-Guest Interaction Studies of π-Stacking Self-Assembled Porous Organic Framework

Abstract

Two naphthaldehyde based fluorescent Schiff bases were designed and synthesised successfully. 2-hydroxy naphthaldehyde and 2-methoxy naphthaldehyde were used for the reactions among which we successfully crystallised the one made with former one. The crystalline structure analysed by single crystal X-ray diffraction study which revealed a chiral non-centrosymmetric space group Trigonal R3c having the polar point group C3V. This is an unusual highly pi-stacked organic discrete framework with six-fold quadrupolar helical arrangement. The single left handedness of the helix was supported by the solid state Circular Dichroism (CD) measurement showing the negative cotton effect and also the Flack parameter of 0.23 is a strong statistical Single Crystal X-Ray Diffraction (SC-XRD) analysis evidence of single handed helical structure. The crystalline form contains the trapped solvent guest molecules i.e. DMF, Acetonitrile and some water molecules making the capsule shaped void with small opening apertures to the surfaces. This is a stable pi-stacked framework up to the 225°C showed no porosity with 8.5 ml of CO2 uptake at 195 K. It showed a potential fluorescence enhance properties when interacting with electron rich aromatic guests and quenching with electron deficient Nitrobenzene, which make it a promising material for detail exploration of its sensing ability of nitro-explosives.