Significantly boosting circularly polarized luminescence by synergy of helical and planar chirality

To get large dissymmetric factor (g_lum) of organic circularly polarized luminescence (CPL) materials is still a great challenge. Although helical chirality and planar chirality are usual efficient access to enhancement of CPL, they are not combined together to boost CPL. Here, a new tetraphenylethylene (TPE) tetracycle acid helicate bearing both helical chirality and planar chirality was designed and synthesized. Uniquely, synergy of the helical chirality and planar chirality was used to boost CPL signals both in solution and in helical self-assemblies. In the presence of octadecylamine, the TPE helicate could form helical nanofibers that emitted strong CPL signals with an absolute g_lum value up to 0.237. Exceptionally, followed by addition of para-phenylenediamine, the g_lum value was successively increased to 0.387 due to formation of bigger helical nanofibers. Compared with that of TPE helicate itself, the CPL signal of the self-assemblies was not only magnified by 104-fold but also inversed, which was very rare result for CPL-active materials. Surprisingly, the interaction of TPE helicate with xylylenediamine even gave a gel, which was transformed into suspension by shaking. Unexpectedly, the suspension showed 40-fold stronger CPL signals than the gel with signal direction inversion each other. Using synergy of the helical chirality and planar chirality to significantly boost CPL intensity provides a new strategy in preparation of organic CPL materials having very large g_lum value.