Recently we have developed an unsymmetrical azobenzene disulfide with a short alkyl side chain, 4-hexyl-4′-(12-(dodecyldithio)-dodecyloxy)azobenzene (C6AzSSC12), aiming of a high efficiency in photoisomerization in SAMs on planar gold surfaces (Tamada, K.; et al. Langmuir 2002, 18, 5239). In this paper, we introduce an additional modification on the molecule to improve the thermal endurance for the photoreaction by attachment of a methyl group to the azobenzene ring, thus avoiding dye aggregation sterically. A "methyl-derivatized" azobenzenethiol (C6Az(Me)SH) SAM revealed a significant improvement in their photoreactivity compared with an unmodified azobenzenethiol (C6AzSH) SAM due to the steric effect of the methyl group. A "methyl-derivatized" unsymmetrical azobenzene disulfide (C6Az(Me)SSC12) SAM exhibited quite a similar photoresponse to that of C6AzSSC12 SAM before heat treatment owing to the free volume given by the unsymmetrical structure; however, only the C6Az(Me)SSC12 SAM could retain high photoreactivity in phase-segregated domains formed by annealing, unlike the C6AzSSC12 SAM. The C6Az(Me)SH and C6Az(Me)SSC12 SAMs exhibited a reaction kinetics different from that of C6AzSSC12 SAM due to a different quantum yield and the molecular tilt angle of the azobenzene unit. The C6Az(Me)SH SAM exhibited a typical character of "congested surface", where the reaction rate from cis to trans was faster, while that from trans to cis was slower compared with those of C6Az(Me)SSC12 SAM.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Surfaces and Interfaces