Consideration of Azobenzene-Based Self-Assembled Monolayer Deposition Conditions for Maximizing Optoelectronic Switching Performances

Photochromic molecules, which change their molecular structure under external stimuli, are promising for increasing the device functionality without consuming additional space. Azobenzene is a typical chromophore that undergoes cis–trans photoisomerization and thus can control the surface dipole moment when applied as a self-assembled monolayer (SAM). A SAM of fluorinated azobenzene (FAZO) is designed for work function tuning of Au by a large dipole moment difference via photoisomerization. For achieving efficient optoelectronic switching, the photoswitching characteristics of FAZO-SAM were investigated according to the processing solvent. Solvents with a higher dielectric constant (ε > 9) could efficiently screen intermolecular electrostatic repulsions and promote the formation of a well-ordered SAM on Au. Interestingly, a well-ordered FAZO-SAM exhibits inefficient photoisomerization because of steric hindrance and/or effective excitonic coupling between adjacent chromophores, while a SAM processed using a marginally polar solvent maximizes the photoswitching efficiency. We present a solvent-based processing protocol of photochromic molecular SAMs to maximize photoelectric switching.