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 K cycl ) 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 K cycl could be shifted according to the amphiphilic polymer employed.