Influence of molecular distortion on the exciton quenching for quaterthiophene-terminated self-assembled monolayers on Au(111)

Deviation from Point Dipole Analysis for Exciton Quenching in Quaterthiophene-Terminated Self-Assembled Monolayers on Au(111)

“…On each XRR distribution, an intensity oscillation, which is a so-called Kiessing fringe, appears due to interference of X-rays reflected at different interfaces. Corresponding to the highly packed standing conformations of the molecules in the 4TC n S-SAMs on Au(111), 25,26 the measured XRR distributions were reproduced well with a bilayer model that included the 4T layer (thickness of d 4T ) and the alkanethiolate layer (thickness of d Alk ), as shown in Figure 2. For the bilayer model, the total reflectivity is described by the sum of the X-rays reflected at three interfaces: the vacuum/4T interface (top surface of SAM), the 4T/alkanethiolate interface, and the alkanethiolate/ Au interface (bottom interface of SAM).…”

“…This may be a result of the skewed alkylene chains under geometrical conflict between the standing 4T and the sp 3 -like Au−S−C anchor structure, as expected from the IRAS results. 26 From the XRR experiments, as described above, we obtained the precise d Alk and d 4T values for all prepared 4TC n S-SAMs, irrespective of the n parity. This provides a great advantage for quantitatively examining the quenching process as a function of d.…”

“…In our studies, we focused on quaterthiophene (4T)-terminated alkanethiolate SAMs (4TC n S-SAMs, where n is the number of methylene units; n = 3, 5, 6, 7, 8, 9, and 13) on the Au(111) surface. 25,26 The morphology of the top of the 4TC n S-SAM was confirmed to be almost atomically flat according to scanning tunneling microscopy (STM), and the orientation of 4T groups was confirmed to be a standing form on the surface according to infrared reflection absorption spectroscopy (IRAS). 25,26 These results suggest that a highly uniformly packed and standing forms of both the 4T and the alkanethiolate moieties were secured in the 4TC n S-SAMs on Au(111).…”

“…To quantitatively elucidate the quenching process in nanostructured organic–inorganic interfaces, we investigated the dynamics of photoexcited electrons in functional self-assembled monolayers (SAMs). , Alkanethiolate-based SAMs on noble metal substrates provide highly packed and chemically stable adlayers with substituent functional groups; hence, these are widely utilized as a prototype of functional molecular systems from both fundamental and application aspects. − ,− As a feature of these systems, the functional end groups can be ordered in molecular conformation, orientation, and two-dimensional arrangement. In our studies, we focused on quaterthiophene (4T)-terminated alkanethiolate SAMs (4TC n S-SAMs, where n is the number of methylene units; n = 3, 5, 6, 7, 8, 9, and 13) on the Au(111) surface. , The morphology of the top of the 4TC n S-SAM was confirmed to be almost atomically flat according to scanning tunneling microscopy (STM), and the orientation of 4T groups was confirmed to be a standing form on the surface according to infrared reflection absorption spectroscopy (IRAS). , These results suggest that a highly uniformly packed and standing forms of both the 4T and the alkanethiolate moieties were secured in the 4TC n S-SAMs on Au(111). Hence, the distance between the 4T group and the Au surface can be controlled by the length of the alkylene chains, i.e., n of −(CH 2 ) n –.…”

“…To investigate the dynamics of photoexcited states at the organic–inorganic interface, time-resolved 2PPE (TR-2PPE) spectroscopy is a powerful tool to directly observe excited electrons and their time evolution. ,,, Using the TR-2PPE method, we examined the quenching rate as a function of n for 4TC n S-SAMs on Au(111). , As a result, the single-exponential decay of the excited states for each n was observed, and then their lifetimes τ depending on n were accurately estimated from each decay curve. In contrast to the simple quenching process of 4TC n S-SAM systems, multiple quenching processes appear for oligothiophene thin film systems depending on the molecular film thickness. , This behavior is possibly due to the nonuniformity of the molecules adsorbed on different layers and the existence of individual dominant decay channels at different layers in the thin films.…”