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

Spectroscopic Evidence of Work Function Alterations Due to Photoswitchable Monolayers on Gold Surfaces

Taking advantage of surfaces’ response to interfacial dipoles, a class of photochromophores (dihydroindolizine) is demonstrated to alter the work function of the underlying substrate (∼170 meV). This same molecule also provides spectroscopic signatures for correlating the change in molecular structure to the induced change in the surfaces’ electronic properties. Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) allows analysis of the characteristic dihydroindolizine CC (1559 cm^–1) and pyridinium (1643 cm^–1) stretch as a function of photoexcitation. Structural assignments of this photochromophore are corroborated to density function theory calculations. Conformational changes in the monolayers appear in parallel with work function changes and are consistent with both its rate and magnitude