Rational design of pH-responsive near-infrared spirocyclic cyanines: the effects of substituents and the external environment.

pH-responsive spirocyclic cyanine dyes were designed and synthesized. The equilibrium constant for cyclization (p) could be rationally controlled by changing the nucleophilic moiety and the side chains. Encapsulation in polymeric micelles inhibited the H-aggregation of the dye, and the p could be shifted according to the amphiphilic polymer employed.