Functionalized 3-pyrrolyl boron-dipyrromethenes

A series of mono-functionalized 3-pyrrolyl boron-dipyrromethenes containing functional groups such as bromo, formyl, cyano, nitro and trimethylsilylacetylene groups at the alpha-position of the uncoordinated pyrrole group were synthesized. Further to show the use of functionalized 3-pyrrolyl BODIPY, we treated alpha-bromo BODIPY with four different boronic acids such as phenyl, biphenyl, phenylacetyl and thienyl boronic acids under mild Pd(0) coupling conditions to afford alpha-aryl substituted 3-pyrrolyl BODIPYs. alpha-Dipyrromethanyl substituted 3-pyrrolyl BODIPY was synthesized by treating alpha-formyl 3-pyrrolyl BODIPY with pyrrole in the presence of TFA in CHCl3. The 3-pyrrolyl BODIPY appended with BODIPY (BODIPY dyad) at the alpha-position of uncoordinated pyrrole was synthesized by oxidizing 3-dipyrromethanyl BODIPY with DDQ followed by complexation with BF3 center dot 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 alpha-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.