Photoactivatable Anthracenes

Fifteen
substituted maleimide cycloadducts of anthracene derivatives
were synthesized in one or two steps from available precursors in
yields ranging from 32 to 63%. They differ in the nature of the group
on the maleimide nitrogen atom and of the substituents on the anthracene
platform. In all instances, the introduction of a maleimide bridge
across positions 9 and 10 of the anthracene skeleton isolates electronically
its peripheral phenylene rings and suppresses its characteristic fluorescence.
The cycloadducts with a 4-(dimethylamino)­phenyl group on the maleimide
nitrogen atom undergo retro-cycloaddition upon ultraviolet illumination
with quantum yields ranging from 0.001 to 0.01. This structural transformation
restores the aromatic character of the central ring of the oligoacene
chromophore and activates its emission with fluorescence quantum yields
ranging from 0.07 to 0.85. Thus, this particular choice of building
blocks for the construction of photoresponsive compounds can translate
into viable operating principles for fluorescence activation and,
ultimately, lead to the realization of valuable photoactivatable fluorophores
for imaging applications.