Luminescent Dipyrrinato Complexes of Trivalent Group 13 Metal Ions

Although free dipyrrins (dipyrromethenes) do not strongly luminesce, certain dipyrrinato complexes of BF2 and
zinc(II) are known to be intensely luminescent species. Two new dipyrrinato fluorophores, based on complexes
with gallium(III) and indium(III), are described. Using a previously described meso-mesityl-substituted dipyrrin, namely
5-mesityldipyrrin (mesdpm), the complexes [Ga(mesdpm)3] and [In(mesdpm)3] were prepared and structurally
characterized. The complexes display the expected octahedral geometry about the metal ions. In some solvents,
such as hexanes, the complexes emit green light upon excitation with UV light at room temperature, with quantum
yields of 2.4% ([Ga(mesdpm)3]) and 7.4% ([In(mesdpm)3]) and lifetimes in the low nanosecond range. Observations
are consistent with assignment to ligand-localized transitions, and this interpretation is further confirmed by density
functional calculations described herein. The new complexes are important additions to the widely used family of
dipyrrin-based fluorescent species and show that dipyrrinato complexes containing metals other than BF2 and
zinc(II) may be useful fluorophores.