Ferrocene-based light-responsive carbon nanohoops

This thesis investigates the synthesis,structural characteristics, and photochemical behavior of cycloparaphenylenes(CPPs), with a focus on ferrocene-containing nanohoops (Fc[n]CPPs). Aninitial section examines an alternative protecting-group strategy for accessingprecursors of highly strained nanohoops, showing that sterically demandingsilyl groups such as tert-butyldimethylsilyl (TBDMS) offer robust andselective reactivity under mild conditions. The central part of this workdescribes the preparation and characterization of Fc[n]CPPs (n =6–8). The most strained member, Fc[6]CPP, exhibits exceptional photochemicalFe²⁺ uncaging under visible-light irradiation inthe presence of 1,10-phenanthroline, forming [Fe(phen)₃]²⁺ in high yield, including in aqueous media. Quantum-yield measurementsreveal a thousand-fold enhancement in reactivity relative to unstrainedferrocene, consistent with rapid nucleophilic interception of the nanohoop’striplet excited state. Furthermore, a comparative analysis of spectroscopic,electrochemical, and computational properties of Fc[n]CPPs (n =6–8) shows that efficient Fe–cyclopentadienyl (Fe–Cp) dissociation is retainedeven in less distorted systems. These data suggest that kinetic factors inducedby strain, rather than metallocene distortion alone, govern reactivity acrossthe series. Synthetic efforts toward the highly strained Fc[5]CPP successfully yieldedthe corresponding pro-aromatic precursor. Although final aromatization remainschallenging, the target nanohoop was observed for the first time. Finally, thesynthesis of ansa-bridged ferrocene nanohoops (a-Fc[6]CPP and a-Fc[8]CPP)is reported. These enantiopure nanoscrolls exhibit up to 20-fold enhancedvisible-light-induced Fe²⁺ uncaging, underscoring the stronginfluence of a conformational lock on metallocene photoreactivity andhighlighting the broader potential of CPP strain engineering for controlledphotoactivation.