Adjustable 2-cyano-3,4-difluoro-1H-pyrrole-based luminescent liquid crystals: Synthesis, properties and substituent effect

Abstract

A series of new tolane-based luminescence liquid crystals (LLCs) constituting of 2-cyano-3,4-difluoro-1H-pyrrole (CN-2F) as the key molecular rigid core have been prepared in high yield. These new LLCs tend to have strong luminescence both in solid/solution state, and emitted color could be modified from blue to green by variation of the substituents at terminal benzene. These new compounds exhibit Nematic/Sematic A phases, good thermal stabilities and high clearing points. The LLCs with strong electron withdrawing substituent on the terminal benzene has narrow HOMO-LUMO energy gap and low dipole moment based on theoretical calculations. The structure of NH2-CN-2F was investigated using single crystal X-ray diffraction analysis. Molecules adopt the head to tail stacking pattern to avoid the π-π aggretion due to extensive hydrogen/weak bonding between the CN-2F core structure and terminal substituent/benzene ring. These results show that 2-cyano-3,4-difluoro-1H-pyrrole can be used as a simple and efficient acceptor chromophore in the development of new solid luminescent and display materials.