Functionalized 3-pyrrolyl boron-dipyrromethenes

Abstract

A series of mono-functionalized 3-pyrrolyl boron-dipyrromethenes containing functional groups such as bromo, formyl, cyano, nitro and trimethylsilylacetylene groups at the α-position of the uncoordinated pyrrole group were synthesized. Further to show the use of functionalized 3-pyrrolyl BODIPY, we treated α-bromo BODIPY with four different boronic acids such as phenyl, biphenyl, phenylacetyl and thienyl boronic acids under mild Pd(0) coupling conditions to afford α-aryl substituted 3-pyrrolyl BODIPYs. α-Dipyrromethanyl substituted 3-pyrrolyl BODIPY was synthesized by treating α-formyl 3-pyrrolyl BODIPY with pyrrole in the presence of TFA in CHCl₃. The 3-pyrrolyl BODIPY appended with BODIPY (BODIPY dyad) at the α-position of uncoordinated pyrrole was synthesized by oxidizing 3-dipyrromethanyl BODIPY with DDQ followed by complexation with BF₃·Et₂O. All compounds were characterized by HRMS mass, NMR, absorption, electrochemical and fluorescence techniques. The spectral studies indicated that the presence of substituent at the α-position of uncoordinated pyrrole of 3-pyrrolyl BODIPY alter the electronic properties of the BODIPY core. The photophysical studies on BODIPY dyad indicated a possibility of energy transfer from the appended BODIPY unit to the 3-pyrrolyl BODIPY unit in BODIPY dyad.