Green-, red- and infrared-emitting polymorphs of sterically hindered push-pull substituted stilbenes

Abstract

The synthesis, XRD single crystal structure, powder XRD and solid-state fluorescence of two new DPA-DPS-EWG derivatives (DPA = diphenylamino, DPS = 2,5-diphenyl-stilbene, EWG = carbaldehyde or dicyanovinylene) is described. Absorption and fluorescence maxima in solvents of various polarity show bathochromic shift with respect to parent DPA-stilbene-EWGs. Electronic coupling in dimers and potential twist elasticity of monomers were studied by density functional theory. Both polymorphs of CHO derivative emit green fluorescence (527 and 550 nm) of moderate intensity (10 % and 5 %) in polycrystalline powder form. Moderate (5 %) red (672 nm) monomer-like emission was also observed for the first polymorph of DCV derivative, while more intense (32 %) infrared (733 nm) emission of the second polymorph was ascribed to the excimer fluorescence.