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Langmuir. 2018 May 29;34(21):6003-6009. doi: 10.1021/acs.langmuir.8b00418. Epub 2018 May 15.

In Situ Observations of UV-Induced Restructuring of Self-Assembled Porphyrin Monolayer on Liquid/Au(111) Interface at Molecular Level.

Kim Y1,2, Doh WH2, Kim J1,2, Park JY1,2.

Author information

1
Graduate School of Energy, Environment, Water, and Sustainability (EEWS) , Korea Advanced Institute of Science and Technology (KAIST) , Daejeon 34141 , Republic of Korea.
2
Center for Nanomaterials and Chemical Reactions , Institute for Basic Science (IBS) , Daejeon 34141 , Republic of Korea.

Abstract

Porphyrin-derived molecules have received much attention for use in solar energy conversion devices, such as artificial leaves and dye-sensitized solar cells. Because of their technological importance, a molecular-level understanding of the mechanism for supramolecular structure formation in a liquid, as well as their stability under ultraviolet (UV) irradiation, is important. Here, we observed the self-assembled structure of free-base, copper(II), and nickel(II) octaethylporphyrin formed on Au(111) in a dodecane solution using scanning tunneling microscopy (STM). As evident in the STM images, the self-assembled monolayers (SAMs) of these three porphyrins on the Au(111) surface showed hexagonal close-packed structures when in dodecane solution. Under UV irradiation (λ = 365 nm), the porphyrin molecules in the SAM or the dodecane solution move extensively and form new porphyrin clusters on the Au sites that have a high degree of freedom. Consequently, the Au(111) surface was covered with disordered porphyrin clusters. However, we found that the porphyrin molecules decomposed under UV irradiation at 254 nm. Molecular-scale observation of the morphological evolution of the porphyrin SAM under UV irradiation can provide a fundamental understanding of the degradation processes of porphyrin-based energy conversion devices.

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