An ionically driven molecular IMPLICATION gate operating in fluorescence mode

An asymmetrically core-extended boron-dipyrromethene (BDP) dye was equipped with two electron-donating macrocyclic binding units with different metal ion preferences to operate as an ionically driven molecular IMPLICATION gate. A Na+-responsive tetraoxa-aza crown ether (R-2) was integrated into the extended pi system of the BDP chromophore to trigger strong intramolecular charge transfer (ICT2) fluorescence and guarantee cation-induced spectral shifts in absorption. A dithia-oxa-aza crown (R-1) that responds to Ag+ was attached to the meso position of BDP in an electronically decoupled fashion to independently control a second ICT1 process of a quenching nature. The bifunctional molecule is designed in such a way that in the absence of both inputs, ICT1 does not compete with ICT2 and a high fluorescence output is obtained (In-A= In-B = 0 -> Out = 1). Accordingly, binding of only Ag+ at R-1 (In-A= 1, In-B= 0) as well as complexation of both receptors (In-A = In-B = 1) also yields Out = 1. Only for the case in which Na+ is bound at R-2 and R-1 is in its free state does quenching occur, which is the distinguishing characteristic for the In-A= 0 and In-B = 1 -> OUt = 0 state that is required for a logic IMPLICATION gate and Boolean operations such as IF-THEN or NOT.