BODIPY–Bacteriochlorin Energy Transfer Arrays: Toward Near-IR Emitters with Broadly Tunable, Multiple Absorption Bands

A series of energy transfer arrays, comprising a near-IR absorbing and emitting bacteriochlorin, and BODIPY derivatives with different absorption bands in the visible region (503–668 nm) have been synthesized. Absorption band of BODIPY was tuned by installation of 0, 1, or 2 styryl substituents [2-(2,4,6-trimethoxyphenyl)­ethenyl], which leads to derivatives with absorption maxima at 503, 587, and 668 nm, respectively. Efficient energy transfer (>0.90) is observed for each dyad, which is manifested by nearly exclusive emission from bacteriochlorin moiety upon BODIPY excitation. Fluorescence quantum yield of each dyad in nonpolar solvent (toluene) is comparable with that observed for corresponding bacteriochlorin monomer, and is significantly reduced in solvent of high dielectric constants (DMF), most likely by photoinduced electron transfer. Given the availability of diverse BODIPY derivatives, with absorption between 500–700 nm, BODIPY–bacteriochlorin arrays should allow for construction of near-IR emitting agents with multiple and broadly tunable absorption bands. Solvent-dielectric constant dependence of Φ_f in dyads gives an opportunity to construct environmentally sensitive fluorophores and probes.