Bidirectional switching of near IR emitting boradiazaindacene fluorophores.

Two novel distyryl-boradiazaindacene dyes with dimethylaminostyryl and pyridylethenyl substituents display opposite spectral shifts on protonation with TFA in organic solvents. This bidirectional switching of the dyes can be shown to be directly related to ICT donor and acceptor characteristics of the substituents attached to the BODIPY core. The observed spectral response of these dyes could be very useful in the design of novel NIR fluorescent ratiometric probes for pH.