Circularly Polarized Room Temperature Red Phosphorescence from a [9]-Heterohelicene Diimide

Abstract

Circularly polarized room temperature phosphorescence (CP-RTP) in the red region is fascinating, however, challenging to achieve in organic molecules. The difficulty stems from two necessary conditions required to design such molecules. Firstly, achieving circularly polarized luminescence, with higher emission quantum yield in the longer wavelength region is challeng-ing. Secondly, attaining phosphorescence from such molecules under ambient conditions is difficult. Achieving both the cri-teria together in a single molecule is ambitious. In this work, we devise a novel design strategy to realize CP-RTP from a [9]-heterohelicene diimide. The designed molecule possesses helical chirality and an extended conjugation affording chiroptical responses in the red region. Interestingly a four-fold increment in the dissymmetry factor has been achieved by switching the solvent polarity. Furthermore, the incorporation of sulphur atom in the molecular framework facilitates a prolonged emis-sion lifetime of 1.09 ms under ambient conditions, making it the only example of a rylene diimide exhibiting CP-RTP.