Stereochemistry of Bistricyclic Aromatic Enes and Related Polycyclic Systems

Abstract

Bistricyclic aromatic enes (BAEs) and related polycyclic systems are a class of molecular materials that display a rich variety of conformations, dynamic stereochemistry and switchable chirality, color, and spectroscopic properties. This is due to the a subtle interplay of the inherent preference for planarity of aromatic systems and the competing necessity of non-planarity due to intramolecular overcrowding in the fjord regions built into the general molecular structure of BAEs. The conformational, dynamic, and spectroscopic properties may be designed and fine-tuned, e.g., by variation of the bridging groups X and Y, the overcrowding in the fjord regions, extensions of the aromatic system, or other modifications of the general BAE structure, based on the fundamental understanding of the structure-property relationships (SPR). The present review provides an analysis of the conformational spaces and the dynamic stereochemistry of overcrowded bistricyclic aromatic enes applying fundamental symmetry considerations. The symmetry analysis presented here allows deeper insight into the conformations, chirality, and the mechanisms of the dynamic stereochemistry, and will be instrumental in future computational studies.

Heteromerous Bistricyclic Aromatic Enes: Dynamic Stereochemistry of Xanthylidene‐Anthrones

“…The dynamic stereochemistry of BAEs has recently been reviewed and analyzed . In disubstituted heteromerous BAEs, all nonplanar conformations have C 1 symmetry.…”

“…The unique molecular architecture of BAEs gives rise to three basic conformations: twisted ( t ), anti ‐folded ( a ), and syn ‐folded ( s ) (Fig. ) . Homomerous bistricyclic enes (Fig.…”

Variations of bistricyclic aromatic enes: mono-bridged tetraarylethene naphthologs

“…The bridges X and Y play an important role in the relative stability of the three conformations, leading in favorable cases to thermochromism [16][17][18][19]. The stereochemistry of BAEs has very recently been reviewed and analyzed [4].…”

“…1) [1,4]. The intramolecular overcrowding in BAEs [14,15] imposes out-of-plane deformation to alleviate prohibitively close contacts of non-bonded atoms in the fjord regions (C 1 _C 1 0 , C 8 _C 8 0 , C 1 _H 1 0 , C 8 _H 8 0 , H 1 _H 1 0 , H 8 _H 8 0 ).…”

“…Bistricyclic aromatic enes (BAEs) [1][2][3][4] (Fig. 1) have fascinated chemists since the parent BAE bifluorenylidene (1) was synthesized in 1875 [5]; dixanthylene (2) was synthesized in 1895 [6]; and thermochromism, piezochromism, and photochromism were revealed in bianthrone (3) [7,8] and dixanthylene (2) [9].…”