π-Truncation of a Parent Nanographene: Chirally Twisted Green Fluorophores

The twist operation of the π-skeleton would induce left or right handedness. Herein, we report two chirally twisted C₆₄ nanographenes designed by formally erasing two fused benzenes from a parent C₇₆ nanographene. These C₆₄ nanographenes possess two [6]helical units implemented around a central pyrene core in a different arrangement. The π-truncation pulls the emission bands hypsochromically from the red (C₇₆, λ_max = 612 nm) to green (C₆₄, λ_max = 505 and 506 nm) region. Curiously, the +/- sign of circularly polarized luminescence at the S₁ → S₀ transition was reversed between the two C₆₄ nanographenes despite them possessing the same handedness. This is attributed to the slight difference in the arrangement of the two transition dipole moments fluctuating at around 90°, as suggested computationally.