Multiethynyl Corannulenes: Synthesis, Structure, and Properties

Syntheses, crystal structures, ab initio density functional theory computations, and photophysical properties of 1,6-di-, 1,2,5,6-tetra-, and 1,3,5,7,9-pentaethynyl-substituted corannulenes (classes 3, 4, and 5, respectively) are reported. Classes 3 and 4 were prepared from the corresponding corannulenyl bromides and terminal alkynes in excellent yields (nine examples, with yields of 57-92%) using the Sonogarshira reaction. Class 5 was prepared from 1,3,5,7,9-pentacholorocorannulene and trimethylalkynylstannanes using a modification of Nolan's procedure (8 examples, with yields of 45-93%). The molecular packing in crystals of 1,6-diphenylethynyl-2,5-dimethylcorannulene (3-Ph2) displays a polar columnar structure with all of the molecule bowls oriented in the same direction. Similarly, 1,2,5,6-tetrakis(3,5-dimethylphenylethynyl)corannulene 4-Ar(c)5 and 1,3,5,7,9-pentakis(3,5-dimethylphenylethynyl)corannulene 5-Ar(c)5 form columnar structures, but the bowls are oriented in opposing directions. Additionally, the number of attached alkynyl arms is correlated with an increase in bowl depth of the corrannulene nucleus. Most of the aryl derivatives displayed high-quantum-efficiency solution luminescence and variable emission wavelengths that were dependent on the nature of the substitution.