Axial chiral aggregation-induced emission luminogens with aggregation-annihilated circular dichroism effect

Abstract

Axial chiral aggregation-induced emission (AIE) luminogens of (R)-3,3′-BTPE-BINA, (R)-6,6′-BTPE-BINA and (S)-6,6′-BTPE-BINA were synthesized for the first time by covalently attaching the AIE-active tetraphenylethene (TPE) units to the axial chiral binaphthol (BINOL) moieties at their 3,3′- or 6,6′-positions. It was found that the circular dichroism (CD) value when TPE was attached to BINOL at its 3,3′-positions was much larger than that found after its attachment at 6,6′-positions. The resultant AIE-active luminogens (AIEgens) show high quantum yields (up to 42.4%) in their aggregated states. Interestingly, these AIEgens exhibit an abnormal aggregation-annihilation CD (AACD) phenomenon. The decrease in the twisted angle between the two naphthalene rings upon aggregation was rationalized as the cause of this unique effect.