1,2,3- Vs 1,2-Indeno Ring Fusions Influence Structure Property And Chirality Of Corannulene Bowls

The domain of polycyclic aromatic hydrocarbons?PAH?reaches from naphthalene to fullerenes,carbon nanotubes and large sheets of graphene monolayer.Buckybowls are fragments of fullerenes or the end cap of single-walled carbon nanotubes.The curvature of molecular bowls differentiates their structures and physical properties from planer polycyclic aromatic hydrocarbons and opens up unique possibilities for bowl-shape molecules in organic materials applications.This thesis introduces synthesis and properties of eight corannulene derivatives.Annulated corannulenes A-C form via distinct synthetic pathways:?i?Pd-catalyzed sp³CH insertion,?ii?Pd-catalyzed aryl coupling,and?iii?silyl cation-promoted C-F activation/CH insertion.Crystal structure,redox,and photophysical studies elucidate the differing influence of 1,2,3-vs 1,2-indeno ring fusions.Comparing the bowl depths and POAV??-orbital axis vector?angles of A-C with those of corannulene shows that 1,2-indeno ring fusion flattens the bowl,whereas 1,2,3-indeno ring fusion deepens the bowl.Considering reduction potentials,A with two fluorenoid sub-graphs displays a first reduction potential which is close to that of corannulene,whereas C with two fluoranthenoid sub-graphs shows a much lower reduction potential.Here,the hybrid compound,B,shows a reduction potential near the middle if somewhat closer to C,similar to the characterization by bowl-depth.In the case of photophysical properties,A has the highest quantum yield among them.B shows a remarkable similarity to C,distinctly not the midpoint of A and C.As such,A could be considered as the"bigger box"consistent with a longer wavelength absorption.Resolution of B via chiral HPLC?high performance liquid chromatography?gives enantiopure forms,electronic circular dichroism?ECD?and vibrational circular dichroism?VCD?studies of which allow the absolute configuration determination.Furthermore,kinetic studies of enantiomerization in chloroform allows assessment of the bowl-inversion barrier.Deprotonation by LDA?lithium diisopropylamide?generated dianions of A-C.They are long lived in the absence of water and oxygen.THF?tetrahydrofuran?solutions of the dianions were prepared in the glovebox and sealed for removal and spectroscopic studies.In addition to clean ¹H-NMR spectra,these dianions display broad absorption spectra out to 800 nm,and their fluorescence emission is shifted to the NIR?near infrared?region but with less significant quantum yields with respect to their precursors.The broad absorption and long wavelength emission indicate a free electron flow in these anions.Independent treatment of A-C with excess potassium t-butoxide in THF produced the dianion,monoanion,and neutral compounds,respectively.A head-to-head titration of A and B with potassium t-butoxide in THF allow the determination of the differential pKa₁ value to be within a tenth of a pK unit.The experiment showed that proton exchange was slow on the NMR time scale so that integration of the neutral and deprotonated species could be used to assess the relative deprotonation of each component.In summary,three indenocorannulenes were synthesized via three different methods.In particular,the enantiomers of the chiral corannulene B were isolated,the bowl-to-bowl inversion barrier was determined,and the absolute configuration was assigned by comparison of experimental and calculated vibrational circular dichroism spectra.The associated photophysical and electrochemical properties were compared using experimental as well as theoretical methodologies.