Substituent parameters impacting isomer composition and optical properties of dihydroindolizine molecular switches

In an attempt to understand which factors influence constitutional isomer control of 6'- and 8'-substituted dihydroindolizines (DHIs), a series of asymmetric pyridines was condensed with dimethyl spiro[cycloprop[2]ene-1,9'-fluorene]-2,3-dicarboxylate. The substituents on the pyridial derivatives ranged from donating to withdrawing and demonstrated control over the isomeric ratios for all DHIs. Substituent control proved to be selective for the highly donating amino, which exclusively formed the 8' isomer. The same ratios were reproduced via photolytic experiments, which suggested that the condensation reaction is dominated by the product's thermodynamic stability. The electronic influences of the substituents extends beyond isomer control, as it impacts the DHIs' optical properties and electrocyclization (switching) rates to the spiro conformers. Our results allow us to predict the syntheses and properties of future 6'- or 8'-substituted DHIs, molecules that will be applied in understanding the role of the dipole vector orientation to work function switching.