Blue-Emitting Arylalkynyl Naphthalene Derivatives via a Hexadehydro-Diels–Alder Cascade Reaction

We
describe here three alkynyl substituted naphthalenes that display
promising luminescence characteristics. Each compound is easily and
efficiently synthesized in three steps by capitalizing on the hexadehydro-Diels–Alder
(HDDA) cycloisomerization reaction in which an intermediate benzyne
is captured by tetraphenylcyclopentadienone, a classical trap for
benzyne itself. These compounds luminesce in the deep blue when stimulated
either optically (i.e., photoluminescence in both solution and solid
films) or electrically [in a light-emitting diode (LED)]. The photophysical
properties are relatively insensitive to the electronic nature of
the substituents (H, OMe, CO2Me) that define these otherwise
identical compounds. Overall, our observations suggest that the twisted
nature of the five adjacent aryl groups serves to minimize the intermolecular
interaction between core naphthalene units in different sample morphologies.
These compounds represent promising leads for the identification of
others of value as the emissive component of organic LEDs (OLEDs).