Computational studies of ethynyl- and diethynyl-expanded tetrahedranes, prismanes, cubanes, and adamantanes.

B3LYP/6-31+G(d) and MP2/6-31+G(d) computations were performed on a series of ethynyl- and diethynyl-expanded tetrahedranes, prismanes, cubanes and adamantanes. Every ethynyl expansion reduces the ring strain energy of the cage. The deprotonation energies of the cage poly-ynes are exceptionally low; we estimate that the gas-phase deprotonation energy of the diethynyl-expanded cubane is about 309 kcal mol(-1). The ring and cage poly-ynes can serve as effective hosts of either lithium or sodium cation, where the best host maximizes the number of interactions of alkynyl groups with the cation at an ideal distance. Last, the vertical excitation energies of the poly-ynes and their conjugate bases suggest that the alkynyl groups are interacting through space. The poly-ynes express a broad range of absorption energies, indicating that these molecules are potential targets in expressly designed optical applications.