Coumarin based emissive rod shaped new schiff base mesogens and their zinc(II) complexes: synthesis, photophysical, mesomorphism, gelation and DFT studies

ABSTRACT

New homologous series of coumarin Schiff base derived from 6-aminocoumarin and their zinc(II) complexes have been synthesised. The spectroscopic characterisations, photophysical properties, phase transition temperature, characterisation of phase and gelation behaviour are reported. The ligand is non-mesogenic at lower 4-n-alkoxy chain length (n = 4) and mesogenic for longer chains (n > 4). For small chains (n = 5, 7, 8), ligand displays monotropic nematic or nematic-smectic A phase sequences, whereas longer homologues (n = 12, 14, 16 and 18) display only enantiotropic smectic A phase. The ligands and their Zn(II) complexes are fluorescent in nature. Interestingly, ligands exhibit gelation property only in polar solvents, whereas Zn(II) complexes discourage gelation. The effect of 4-n-alkoxy chain length on the gelation properties was also discussed. Density functional theory calculations show broad agreement with observed molecular conformation, dipole moment, molecular orbitals and polarisability of the coumarin Schiff base molecules and their Zn(II) complexes.

GRAPHICAL ABSTRACT

KEYWORDS:

• Coumarin
• Schiff base
• mesogens
• Zn(II) complexes
• photophysical studies
• gelation and computational studies

Acknowledgements

Authors gratefully acknowledge the instrumental facility provided under UGC-SAP and DST-FIST programme, New Delhi.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

S.K.S. is thankful to UGC, New Delhi, for University Research Fellowship.