We have grown 1-dodecandthiol (DDT) monolayer on a bare Si(111) surface through ultraviolet-assisted photochemical reaction. The resulting monolayer was investigated by means of water contact angle measurement, synchrotron radiation-based high-resolution X-ray photoelectron spectroscopy, and polarization-dependent near-edge X-ray absorption fine structure spectroscopy. These combined probes for characterization reveal a hydrophobic ambient surface; the DDT was directly attached to Si through a Si-S bond, and the molecules formed an ordered monolayer with an average tilt angle of 57° of the alkyl chains relative to the substrate surface.

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Producing a fluorescent azobenzene derivative and investigating the relationship between the selfassembled structure and photophysical properties is a challenging topic, which is of significance in material science. Here, we report the light-driven fluorescence enhancement and self-assembled structural characteristics of an azobenzene derivative N-(3,4,5-octanoxyphenyl)-N 0 -4-[(4-hydroxyphenyl) azophenyl]1,3,4-oxadiazole (AOB-t8). A highly fluorescent self-assembled aggregate of cis-AOB-t8 in organic solution under UV light illumination has been observed; the quantum yield can reach 33.7 Â 10 À2 , which is an enhancement of about 306 times compared with that of trans-AOB-t8, which is negligibly fluorescent in the initial nonirradiated solution. It has been proposed that the fluorescence enhancement originates from the trans-to-cis monomeric isomerization and the aggregation of cis-AOB-t8. Based on the theoretical calculations, we have discussed the mechanism for light-driven fluorescence enhancement of the monomeric cis-AOB-t8, which was commendably applied to interpret the observed spectroscopic result. In addition, the formation of the J-aggregate of cis-AOB-t8 leads to further enhancement of the emission. Moreover, this photocontrolled fluorescence enhancement in a concentrated solution (1 Â 10 À3 M) could be attributed to the significant structural changes of the aggregates, from fiber-like aggregates to layer structured aggregates. According to the spectroscopy study, it is suggested that the trans-AOB-t8 is inclined to form H-aggregates and the cis-AOB-t8 forms J-aggregates, which could probably lead to the structural variety related to the different molecular conformations of AOB-t8.