Synthesis of covalently linked boron-dipyrromethene chromophore conjugates using 3-bromo-boron-dipyrromethene as a key precursor

Abstract

3-Bromo boron dipyrromethene (3-bromo BODIPY) has been used as key synthon to prepare one ethynyl bridged and six ethynylphenyl bridged BODIPY–chromophore conjugates using mild Pd(0) coupling conditions. The chromophores possessing very distinct features, such as anthracene, BODIPY, terpyridine, porphyrin, Zn(II)porphyrin, 21,23-dithiaporphyrin and thiasapphyrin were connected at 3-position of boronboron–dipyrromethene dye by coupling of 3-bromo BODIPY with ethynyl or ethynylphenyl chromophore in toluene/triethylamine in the presence of catalytic amount of AsPh₃/Pd₂(dba) ₃ at 40 °C followed by column chromatographic purification. The spectral studies indicated that the interaction is stronger in ethynyl bridged BODIPY–chromophore conjugate compared to ethynylphenyl bridged BODIPY–chromophore conjugates. The steady-state fluorescence indicated that in ethynyl bridged BODIPY–anthracene conjugate, the BODIPY unit act as energy acceptor and showed a possibility of energy transfer from donor anthracene unit to acceptor BODIPY unit on selective excitation of anthracene unit. However, in ethynylphenyl bridged BODIPY–porphyrin conjugates, the BODIPY unit act as energy donor and exhibited a possibility of singlet-singlet energy transfer from BODIPY unit to porphyrin unit.