A borindolizine platform for the design of fluorophores with tunable emissions

A new boron-containing heterocyclic scaffold – borindolizine – is reported as a new heterocyclic scaffold with broadly tunable fluorescence and a high Stokes shift. Two classes of emitters were synthesized through rational scaffold changes resulting in blue-emitting carboxyborindolizines (λmax,em = 431 – 459 nm) and green emitting aryl borindolizines (λmax,em = 488 – 519 nm). Experimental structure-emission trends were used to validate a computational spectral prediction model and subsequently used to design a red-emissive fluorophoric scaffold. A red-emissive (λmax,abs = 370 nm, λmax,em = 635 nm) isoquinolyl borinidolizine was synthesized in excellent agreement with the theoretical emission (λmax,em = 621 nm). These results establish borindolizine as a highly attractive class of fluorescent heterocycle with a highly tunable emission, allowing for custom fluorophore synthesis.