Abundant lattice inclusion phenomenon with sterically hindered and inherently shape-selective tetraarylpyrenes

Abstract

Tetraarylpyrenes H1-H4 that typify molecular systems with orthogonal planes and lack hydrogen bonding functional groups were designed as new host systems with three distinct domains for guest inclusion. In particular, H2 and H4 hosts are found to include a variety of guest molecules. We have determined 42 crystal structures overall (i) to establish the importance of skeletal features of the hosts, (ii) to determine their adaptability in binding diverse guest molecules, and (iii) to delineate favored domains for location of guest molecules and preferred modes of association of the host systems. The unique features of H1-H4 are found to permit binding of aliphatic and aromatic guest species differently: the small-sized guest molecules such as CHCl₃, (CH₃)₂S, etc. are found to be bound in the basin domain, whereas aliphatic and aromatic guests are found to be included in the channel/concave and trough regions, respectively. The crystal structure analyses reveal that as many as 20 out of 28 inclusion compounds of H2 are isostructural with one or more; we have identified 8 different crystal packing types with which each inclusion compound may be associated. The guest-binding potential of host H2 has been exploited to demonstrate the utility of these host systems in (i) the separation of regioisomeric methyl-substituted benzenes and mixtures of cis-trans isomers of decalin, perhydroisoquinoline, and cinnamonitrile, (ii) the stabilization of the keto-enol form of 1,3-diketones, and (iii) the conformational locking of flexible cycloalkanes.