Pyrene-cored blue-light emitting [4]helicenes: synthesis, crystal structures, and photophysical properties

The synthesis, crystal structures and photophysical properties of two types of pyrene-cored blue-light emitting [4]helicenes (7 and 9) are reported. The chemical structures of all synthesized compounds were fully confirmed by H-1 and C-13 NMR spectra, mass spectroscopy as well as elemental analysis. Single-crystal X-ray analysis of these [4] helicenes revealed that there are two types of laterally naphthalene annulated helical architectures, which are clearly influenced by different R substituents. The photophysical properties of the [4]helicenes (7 and 9) were fully investigated in both solutions and films, along with the pre-cyclization products, 4,9- and 4,10-bis(phenylethenyl)pyrenes (6 and 8). Notable optical features were obtained in these compounds, which make them promising candidates for several important applications in modern electronic and optoelectronic devices, such as blue emitters in organic light-emitting devices (OLEDs), or as models for further exploring the development of a new generation of organic materials based on pyrene.