Aggregation-Induced Emission in Organic Ion Pairs

The ion pairs described in this chapter consist in a charged potentially-fluorescent dye, associated with a spectroscopically-silent organic counter-ion. Their combination with the novel AIE phenomenon provides a few distinct advantages, particularly in terms of sensitivity and selectivity. Such systems are highly versatile. Counter-ions strongly influence the molecular arrangement of the salts, and hence the fluorescence properties. The easy permutation of the counter-ions while keeping the same fluorophore allows these properties to be precisely controlled. The preparation of ion pairs and the type of interactions involved were discussed. Organic salts are known to be particularly hydrophobic. Their in situ formation in water generates suspensions of nano- and microparticles, which can be tailor-made for subsequent use. In addition, since many analytes of biological interest are electrolytes and polyelectrolytes, the interaction with charged AIE-active luminogens leads to new systems of analysis and structural investigation.