3D Coumarin Systems Based on [2.2]Paracyclophane: Synthesis, Spectroscopic Characterization, and Chiroptical Properties

In this article, we report the preparation of a series of [2.2]­paracyclophane-fused coumarin systems through a simple and general procedure involving a transition-metal-catalyzed cyclization of aryl alkynoates as the key step. We also highlight the influence of the [2.2]­paracyclophane (pCp) motif and its “phane” interactions on the spectroscopic properties of the newly synthesized fluorophores, which emit in the blue-green region of the visible spectrum (λ_em up to 560 nm) and show extremely large Stokes shifts (up to 230 nm). Finally, we demonstrate that our straightforward approach can easily be used to access optically active planar chiral 3D coumarins. Compared to previously described fluorescent paracyclophanes and other organic dyes, our compact heteroaromatic derivatives show promising chiroptical properties, both in term of circular dichroism (g_abs ∼ 8 × 10 ^–3) and circularly polarized luminescence (g_lum ∼ 5 × 10 ^–3), thus demonstrating a practical application of our synthetic method.