Synthesis and photophysical properties of pyrene-based light-emitting monomers: highly pure-blue-fluorescent, cruciform-shaped architectures

A new series of pyrene-based, pure-blue, fluorescent, stable monomers, namely 2,7-di-tert-butyl-4,5,9,10-tetrakis(p-R-phenylethynyl)pyrenes, have been successfully synthesised by Pd/Cu-catalysed Sonogashira coupling in excellent yield. The cruciform-shaped, π-conjugated structures were fully characterised by 1H/13C NMR and IR spectroscopy, mass spectrometry and elemental analysis. As revealed from single-crystal X-ray analysis, there is a herringbone pattern between stacked columns, but the π-π stacking distance of adjacent pyrene units was not especially short at about 5.82 Å due to the introduction of the two bulky tBu groups in the pyrene rings at the 2- and 7-positions. The photophysical properties of these monomers were carefully examined in different organic solvents, and these data strongly indicate their promising application as blue-emitting materials in organic light-emitting diodes (OLEDs).