Synthesis and optical/thermal properties of low molecular mass V-shaped materials based on 2,3-dicyanopyrazine

A novel series of luminescent low molecular mass materials containing a 2,3-dicyanopyrazine central core were synthesized through an esterification reaction between diphenol 10 and different aromatic carboxylic acids 1-6, containing terminal long alkyl chains. They have a similar V-shaped geometry with lack of planarity between the two arms, confirmed by the X-ray structure of the central core. The optical and thermal properties of these compounds were evaluated. They show blue fluorescence in solution ( 440-480 nm) with quantum fluorescence yields (Φ_F) from 0.003 to 0.1 and Stokes shifts of around 90 nm. In solid state, optical band gaps (E_g) were from 3.14 to 3.32 eV. Thin films of 11, 13, and 14 exhibited blue fluorescence ( 430-456 nm), and 12, 15, and 16 (more bulky) displayed green fluorescence ( 488-512 nm). Most of the materials exhibited good thermal stability, exhibiting an amorphous glassy state after melting. Transparent amorphous films were easily obtained through spin coating and characterized by AFM analysis.