Functional Heptagon-Centred Polyaromatics

Although normally associated with neutral carbon frameworks, aromaticity can also be found in charged systems. Carbon frameworks bearing unsaturated, odd-numbered rings are known to exhibit the same type of stabilising electron delocalisation as traditional aromatics when they hold a positive or negative charge. High impact neutral carbon materials such as graphene can be modified to possess the unique properties of charged aromatic systems through implementing unsaturated odd numbered rings (aromatic ions). We are attempting to achieve this by building an extended nanographene from a central tropylium cation providing a redox-active polycyclic aromatic hydrocarbon (Figure 1a). Synthesising a family of cycloheptatriene centred molecular rotor precursors also allows us to study the photophysical properties associated with charged, aromatic molecular rotors. The photoluminescence of phenyl-ring molecular rotors bearing seven phenyl groups are reported to originate, not from the localized excited state as one might expect, but from unanticipated through-space aromatic-dimer states.2 This Thesis will discuss investigations into the structure-property relationships of cycloheptatriene embedded molecular rotors. The applications of heptaphenylcycloheptatriene have been discussed through Chapters 2-4 with key findings revealing the importance of modifying both the central and peripheral rings of these molecular rotors in tuning their chemical and photophysical properties.