Trannulenes with “In‐Plane” Aromaticity: Candidates for Harvesting Light Energy

Abstract

Breaking with convention: In the textbook aromatic annulenes the p orbitals are oriented perpendicular to the ring plane. In trannulenes the p orbitals form a cyclic, conjugated π system within the ring plane (see scheme). This concept of “in‐plane” aromaticity was first recognized in 1979, and now representative compounds have been synthesized. The all‐trans configuration of the annulene ring is stabilized by a fullerene framework, and the novel physicochemical properties of trannulenes open new opportunities for the design of light‐harvesting compounds.

Double Aromaticity in Monocyclic Carbon, Boron, and Borocarbon Rings Based on Magnetic Criteria

“…[4, Further early conceptual examples of double aromaticity included the illustrative C 10 H 5 À (10 p + six rad) and C 8 H 4 (10 p + two rad) proposals ( Figure 2); numerous in-plane candidates were also suggested. [4] The trannulenes (cyclically conjugated trans polyenes; an example is shown in Figure 2) were predicted as a class of in-plane aromatics [4,11,[32][33][34] and an increasing number of experimental verifications now exist. [33,[35][36][37] More recently, Schleyer et al [38] re-examined and analyzed the structures and magnetic properties of the 3,5-dehydrophenyl cation (C 6 H 3 + ) and the closely related cyclo [6]carbon (C 6 ) in greater detail.…”

Exploration of Nano‐Saturns: A Spectacular Sphere–Ring Supramolecular System

“…In alkene ring 7 ([36]annulene), the sp 2 carbons direct their p‐orbitals to the ring center. This structure is fascinating in terms of in‐plane aromaticity, and is sometimes called trannulene . The ring diameter of 7 is 1.39 nm (C⋅⋅⋅C), and the inclusion of a C 60 molecule is an endothermic process (Δ H B −204 kJ mol −1 ).…”

“…This structure is fascinating in terms of in-plane aromaticity,a nd is sometimes called trannulene. [47] The ring diametero f7 is 1.39 nm (C···C), and the inclusion of aC 60 molecule is an endothermic process (DH B À204 kJ mol À1 ). The large binding energy is attributed to the strong p-p interactions between the 36 sp 2 carbonsa nd the included C 60 .A lkyne ring 8,acyclocarbon consisting of 36 sp carbons, has ap lanar and circular structure with the ring diameter of 1.48 nm.…”

Synthesis and Spectroscopic Characterization of the First Symmetrically and Nonsymmetrically Substituted Fluorinated Emerald‐Green Trannulenes C60F15R3 Soluble in Polar Media and Water

“…[2] The first experimental evidence for the existence of trannulenes was serendipitously obtained in 2001 by Taylor et al who was studying the derivatization of fluorinated fullerene C 60 F 18 . It was found that carbon anions -CX(COOR) 2 in reactions with C 60 F 18 attach at the δ positions with respect to the carbon atoms bearing the groups could be introduced onto the fullerene cage of C 60 F 15 R 2 RЈ trannulenes with R substituents and then some additional organic functionality could be attached independently with RЈ. The RЈ substituent might potentially comprise a ligand responsible for selective targeting of the whole trannulene molecule to some specific tissues or intracellular structures.…”