Researchers from University of Virginia have investigated the effects of aromatic substituents in boron diketones.
All of the dyes studied except BF2mbm (i.e. those with aromatic rather than aliphatic substitution) showed emission changes upon mechanical perturbation. Aromatics with increased π conjugation led to more dramatic, red-shifted fluorescence. Their recovery is also significantly affected by the aromatic substituents.
Interested to know more? Why not read the full article for free: T. Liu, A. D. Chien, J. Lu, G. Zhang and C. L. Fraser, J. Mater. Chem., 2011, DOI: 10.1039/c0jm04326e (Advance Article)