Synthesis of a Negatively Curved Nanocarbon Molecule with an Octagonal Omphalos via Design-of-Experiments Optimizations Supplemented by Machine Learning.

A saddle-shaped nanocarbon molecule was synthesized, which revealed the existence of negative Gauss curvatures on a >3-nm molecular structure possessing 192 π-electrons. The synthesis was facilitated by a protocol developed with Design-of-Experiments optimizations and machine-learning predictions, and spectroscopy and crystallography were used to reveal the saddle-shaped structure of the molecule. Solution-phase analyses showed the presence of dimeric assembly, and crystallographic analyses revealed the stacked dimeric structures. The stacked crystal structure was scrutinized by various methods, including Gauss curvatures derived from the discrete surface theory of geometry, to reveal the important role of the molecular Gauss curvature in dimeric assembly.

Curved Phenine Normal Vectors: Geometric Measures of Geodesic Phenine Frameworks.

A vector was introduced to quantitatively describe the pyramidalization of 1,3,5-trisubstituted benzene (phenine). The vector, named curved phenine normal vector (CPNV), defined the direction of pyramidalization of the trigonal phenine panel and quantified the degree of pyramidalization. The relative orientation of the two CPNVs further defined a dihedral angle, which quantified interphenine torsions. The CPNV analysis visually showed the geometric features of nanometer-sized molecules by revealing the important role of torsions. Biased electrostatic potentials were also correlated with CPNV pyramidalizations.

Synthesis of a Hemispherical Geodesic Phenine Framework by a Polygon Assembling Strategy.

A synthetic strategy to construct large geodesic structures of phenine (1,3,5-trisubstituted benzene) was devised. In this strategy, five pentagons were assembled on an omphalos pentagon, and bridging peripheral pentagons furnished five additional hexagons. Thirty phenine units were synthetically assembled to afford a large C220 H180 molecule with a phenine framework isoreticular to a hemispherical, bisected segment of C60 . Although a hemispherical structure of the phenine framework was suggested by solution-phase NMR spectra, crystallographic analysis revealed an oval-like deformation of the molecular shape. In-depth structural analyses, including theoretical calculations, showed that structural fluctuations observed as variations in the biaryl torsion angles allowed structural deformations and, at the same time, that the dynamic fluctuations resulted in the spectroscopic observation of a hemisphere as a time-averaged structure.

Synthesis, Structures, and Assembly of Geodesic Phenine Frameworks with Isoreticular Networks of [ n]Cyclo- para-phenylenes.

A series of macrocycles were designed by rendering geodesic phenine frameworks in isoreticular networks of [ n]cyclo- para-phenylenes. Large, nanometer-sized molecules exceeding molecular weights of 2000 Da were synthesized by five-step transformations including macrocyclization of [6]cyclo- meta-phenylene panels. The dependence of both the molecular structures and the fundamental properties on the panel numbers was delineated by a combination of spectroscopic and crystallographic analyses with the aid of theoretical calculations. Interestingly, flexibility of the molecules via panel rotations depends on the hoop size, which has not been disclosed with the small isoreticular [ n]cylco- para-phenylenes. One of the macrocycles served as a host for C70, and its association behaviors and crystal structures were revealed.

Unbiased Rotational Motions of an Ellipsoidal Guest in a Tight Yet Pliable Host.

In the design of machinery such as steel bearings, a fundamental understanding of material characteristics provides an indispensable basis for the design. Although hydrocarbon cycloarylenes have started to be used for providing unique supramolecular bearings with anomalous dynamic behaviors, their fundamental understanding is immature. A unique property of the cycloarylene host is now reported: the cyclic host is so pliable that it tracks the orientational changes of the ellipsoidal guest, that is, C70 fullerene. Unique structures of the complex were revealed by spectroscopic and crystallographic analyses, and additional theoretical investigations deepened our understanding by revealing the structural changes associated with unbiased rotational motions.