Synthesis, crystal structures and photophysical properties of novel boron-containing derivatives of phenalene with bright solid-state luminescence

Abstract

A novel series of boron-containing derivatives of phenalene have been synthesized. These compounds with emission changes from green, yellow to red were obtained by introducing electron-donating or electron-withdrawing substituent groups. Electron density distribution and energy levels of new compounds were calculated by density functional theory. The results show that the HOMO orbitals are delocalized over the whole molecule of the π-conjugated framework, with the LUMO orbitals mainly delocalized over the phenalene plane. The single-crystal structure demonstrates that the bulky substituents prevent the fluorophores forming short intermolecular interactions, which helps to avoid energy loss via non-irradiative decay and benefits enhancing the solid-state fluorescence emission of the compounds. Moreover, keeping intramolecular push–pull electronic structure was found to be also in favor of strengthening the fluorescent intensity of this kind of compounds.