Triisopropylsilylethynyl-Pentacene on Au(111): Adsorption Properties, Electronic Structure, and Singlet Fission Dynamics

Abstract

Oligoacenes have recently received much attention because of their ability to undergo singlet fission, a process which may improve the energy conversion efficiency in organic solar cells. Here, we studied the structural and the electronic properties of triisopropylsilylethynyl-pentacene (TIPS-Pn) adsorbed on Au(111) from monolayer to multilayer coverages using multiexperimental techniques [temperature-programmed desorption, vibrational and electronic high-resolution electron energy loss spectroscopy, and energy- and time-resolved two-photon photoemission (2PPE)]. We demonstrated that well-defined TIPS-Pn molecular films can be prepared via evaporation. TIPS-Pn adopt on Au(111) a molecular adsorption geometry in which the pentacene backbone is oriented parallel to the substrate. We determined the energetic position of several unoccupied and occupied electronic states among others originating from the lowest unoccupied molecular orbital and the highest occupied molecular orbital. Femtosecond time-resolved 2PPE enabled us to resolve the time scales for the singlet fission process, which are coverage-dependent. The present study provides important parameters such as energetic positions of molecular electronic states as well as the electronically excited-state dynamics involved in the singlet fission process, which are essential for designing organic-molecule-based optoelectronic devices.

Electronic structure of an iron porphyrin derivative on Au(1 1 1)

“…The photoemission peak close to the high-energy cut-off can be assigned to the first (n = 1) image potential state (IPS) located 3.87±0.07 eV above E F . This corresponds to an energy of 0.57 eV below the vacuum level, and has been found for other adsorbatecovered Au(111) surfaces [34,23,46,47,48,49].…”

“…The photoemission peak close to the high-energy cut-off can be assigned to the first (n = 1) image potential state (IPS) located 3.87±0.07 eV above E F . This corresponds to an energy of 0.57 eV below the vacuum level, and has been found for other adsorbatecovered Au(111) surfaces [34,23,46,47,48,49]. Figure 5 shows the two-color 2PPE spectra of 1 ML FeTPyP/Au(111) recorded with different photon energies and the corresponding analysis of the photon-energy dependent energetic position of the observed photoemission peaks.…”

Influence of N-introduction in pentacene on the electronic structure and excited electronic states

“…15–28 High-resolution electron energy loss spectroscopy (HREELS) provides the required insight into both adsorption and electronic properties of molecular compounds at interfaces to (semi)conducting surfaces and within thin films. 11,29–39 Depending on the primary energy of the incident electrons molecular vibrations or electronic transitions can be excited, including optically forbidden transitions (singlet to triplet states) as already successfully demonstrated for some organic compounds 40–42 including also the N-heteropolycycle 6,13-diazapentacene (6,13-DAP). 12 While the adsorption and electronic properties of pentacene (PEN) and its derivatives adsorbed on various metallic substrates have been investigated in great detail (see for example ref.…”

Electronic Properties of Tetraazaperopyrene Derivatives on Au(111): Energy-Level Alignment and Interfacial Band Formation

“…Similar shifts have been observed for many organic molecules on Au(111), where charge transfer to the substrate is negligible and ascribed to a modification of the image charge and work function (Φ). 13 , 53 , 82 − 87 Indeed, we find a reduction of the work function for all three molecules, the largest one for TAPP-H by 0.74 eV.…”