Photoexcited State Confinement in Two-Dimensional Crystalline Anthracene Monolayer at Room Temperature

Abstract

Organic thin film electronics place a high demand on bottom-up technology to form a two-dimensionally (2D) functional unit consisting of a single molecular crystalline layer bound to a layered structure. As the strong interaction between a substrate and molecules makes it difficult to evaluate the electronic properties of organic films, the nature of electronic excited states has not been elucidated. Here, we study a 2D crystalline anthracene monolayer electronically decoupled by alkanethiolates on a gold substrate using scanning tunneling microscopy and time-resolved two-photon photoemission spectroscopy and unravel the geometric/electronic structures and excited electron dynamics. Our data reveal that dispersive 2D excited electrons on the surface can be highly coupled with an annihilation of nondispersive excitons that facilitate electron emission with vibronic interaction. Our results provide a fundamental framework for understanding photoexcited anthracene monolayer and show how the coupling between dispersive and nondispersive excited states may assist charge separation in crystalline molecular layers.

Strong Hydrogen Bonds at the Interface between Proton-Donating and -Accepting Self-Assembled Monolayers on Au(111)

“…The imidazole molecule can accept H + at the imino N site and stabilize it as an imidazolium cation. , At the saturation coverage of alkane­thiolate-based SAMs, the molecules are in a closely packed standing-up form and the end group tends toward the open side on the SAM. − For the functional end groups, the molecular orbitals and chemical properties are less perturbed from Au substrates due to the spacer layer of the closely packed alkylene chains in the SAMs. The energy levels of both occupied and unoccupied molecular orbitals for the functional groups are reported to be very similar to those of their molecules. , In the case of Im-SAMs, as expected, the imidazole groups can interact with several types of molecules in solution, − in which the imino N in the imidazole group ligates with metalloporphyrin or heme in cytochrome c as metal complexes. Hence, we deduce that the imino N on Im-SAMs makes hydrogen bonds as H + acceptor sites with H + -donating molecules.…”

“…The energy levels of both occupied and unoccupied molecular orbitals for the functional groups are reported to be very similar to those of their molecules. 14,15 In the case of Im-SAMs, as expected, the imidazole groups can interact with several types of molecules in solution, 16−18 in which the imino N in the imidazole group ligates with metalloporphyrin 17 or heme in cytochrome c 18 as metal complexes. Hence, we deduce that the imino N on Im-SAMs makes hydrogen bonds as H + acceptor sites with H +donating molecules.…”

Role of Initial and Final States in Molecular Spectroscopies: Example of Tetraphenyldibenzoperiflanthene (DBP) on Graphite

“…Similar vibrational structures in 2PPE spectra have been reported previously. 82,83 The satellites are assigned to the molecular vibrations of the final state. We can exclude the initial or intermediate states of the respective 2PPE processes as the cause, because in those cases the satellites should appear at the high-energy sides of the most pronounced peak, which they obviously do not.…”

Vibrational Spectra of Thiolate-Protected Gold Nanocluster with Infrared Reflection Absorption Spectroscopy: Size- and Temperature-Dependent Ordering Behavior of Organic Monolayer

“…Two peaks around 1600 cm –1 (peaks 5 and 6 ) and a peak around 3030 cm –1 (peak 1 ) are missing, and one peak around 1500 cm –1 (peak 7 ) is extremely small in the IRAS spectrum of C2Ph SAM. These missing peaks are attributed to the vibration of the aromatic ring, and the transition dipole moments seem parallel to the plane of the aromatic ring, according to the surface selection rule of IRAS. , Therefore, C2Ph SAM is considered to be in a lying-down structure where the plane of the phenyl group is parallel to an Au(111) surface. Peaks that are observed in C2Ph SAM could be assigned to vibrational modes of the CH 2 groups.…”