Unveiling a New Aspect of Simple Arylboronic Esters: Long-Lived Room-Temperature Phosphorescence from Heavy-Atom-Free Molecules

Arylboronic esters
can be used as versatile reagents in organic
synthesis, as represented by Suzuki–Miyaura cross-coupling.
Here we report a serendipitous finding that simple arylboronic esters
are phosphorescent in the solid state at room temperature with a lifetime
on the order of several seconds. The phosphorescence properties of
arylboronic esters are remarkable in light of the general notion that
phosphorescent organic molecules require heavy atoms and/or carbonyl
groups for the efficient generation of a triplet excited state. Theoretical
calculations on phenylboronic acid pinacol ester indicated that this
molecule undergoes an out-of-plane distortion at the (pinacol)­B–Cipso moiety in the T1 excited state,
which is responsible for its phosphorescence. A compound survey with
19 arylboron compounds suggested that the phosphorescence properties
might be determined by solid-state molecular packing rather than by
the patterns and numbers of boron substituents on the aryl units.
The present finding may update the general notion of phosphorescent
organic molecules.