6-Hydroxyindole-based borondipyrromethene: Synthesis and spectroscopic studies

A 6-hydroxyindole-based BODIPY, named BODIPY-OH, with distinct spectroscopic characteristics is reported. Through a systematic study of the spectroscopic characteristics of BODIPY-OH and BODIPY-O(-) in various solvents containing an organic base, we found that the light-color of the fluorophore can be tuned over a wide range by changing the polarity of solvent/base combinations. The absorption color of the solution can be tuned over a range of 100 nm and the emission color within a wide range from 571 to 681 nm by simply converting the phenol form of BODIPY-OH to the phenolate form. Fluorescence of BODIPY-O(-) with high quantum yield shows relatively large Stokes shift in solvent/base combinations, which are ascribed to the excited state deprotonation from (BODIPY-OH)* to (BODIPY-O(-))*, followed by emission from the ion form.