Molecular switches and dual channel detection of Cd2+ and Fe3+ ions based on a multipodand system.

Abstract

Multipodand conjugates were designed and synthesized and incorporated 5-chloro-8-hydroxyquinoline for efficient performance and fine tuning to behave as molecular switches by the addition of metals ions, protonation, and their combination in CH3 CN and CH3 CN-H2 O. Dipodand 3 and tetrapodand 4 showed a switching 'ON' of fluorescence (λem = 435-445) with Zn2+ and Cd2+ (OR logic) and switching 'OFF' of fluorescence (λem = 402) in the presence of Cu2+ , Co2+ and Ni2+ (NOR logic). 4 showed switching 'OFF' of fluorescence at 402 nm at low concentrations of Ag+ , Pb2+ , Hg2+ and Fe3+ and, on further accumulation of these metal ions, excimer bands at 432 nm (Ag+ ) and 510 nm (Pb2+ , Hg2+ and Fe3+ ) provided the opportunity for 'ON-OFF-ON' switching. In contrast, 3 showed no change with Ag+ , while Pb2+ caused only 'ON-OFF' switching and Hg2+ and Fe3+ ions caused similar 'ON-OFF-ON' switching. The H+ -induced 'ON-OFF-ON' molecular switch was combined with Cu2+ that persuaded NOR logic to mimic inhibit (INH) logic. The compound also exhibited a H+ /Cu2+ -induced 'OFF-ON-OFF' type of signalling pattern. These proton-induced multiple outputs provide opportunities for YES, NOT logic gates. 3 showed selective 'ON-OFF' behaviour with Fe3+ ions and 'OFF-ON' behaviour with Cd2+ ions in 20% HEPES buffer-CH3 CN.