Electron Energy Loss of Terrylene Deposited on Au(111): Vibrational and Electronic Spectroscopy

Abstract

We have investigated the vibrational and electronic properties of terrylene by high-resolution electron energy-loss spectroscopy (HREELS), Fourier-transform infrared spectroscopy, and low-temperature single-molecule fluorescence spectroscopy. Terrylene thin films were sublimated in an ultrahigh vacuum on the Au(111) surface in order to record the HREEL spectra. Polycrystalline pdichlorobenzene was used as a matrix to isolate a single terrylene molecule at 1.5 K and record its fluorescence spectrum. The infrared spectrum, the vibrational components from the fluorescence spectrum, and density functional theory calculations were used for the assignment and identification of the active modes found in HREELS. Finally, we report a loss signal around 17 000 cm −1 (2.1 eV) for the first singlet electronic excited state in agreement with optical spectroscopy. The HREEL spectra show both IR-and Raman-active vibration modes because of specific surface selection rules. Energy-loss spectroscopy could be used as a complementary technique to explore some other degrees of freedom that are not accessible by optical means.

Core Halogenation as a Construction Principle in Tuning the Material Properties of Tetraazaperopyrenes

“…HREELS has been widely used to investigate isomerization processes in molecular switches at surfaces41 or to study 2‐dimensional aromatic molecules on surfaces 41. 42…”

“…This surface‐sensitive method gives insight into the electronic structure of adsorbed molecules, which is needed for an understanding of their properties at surfaces and interfaces, because they appear as important junctions in organic molecule‐based devices. Electronic HREELS has been successfully applied to study organic semiconductors42, 52, 53 and graphene nanoribbons54, 55 on noble metal surfaces. It allows, amongst others, the determination of optical gaps by exciting intramolecular electronic transitions from the ground state (S 0 , HOMO) to the excited state (e.g., S 1 , LUMO).…”

“…[40] HREELS has been widely used to investigate isomerization processes in molecular switchesa ts urfaces [41] or to study 2-dimensionala romatic molecules on surfaces. [41,42] In the following, we presenta nd discuss the data exemplarily for the TAPP-H.T he assignment of all observed vibrational modes and the corresponding spectraf or the halogenated derivatives are shown in the Supporting Information (section1). Figure 4s hows the HREEL spectra of TAPP-H at am ono-(ML) and multilayer coverage.…”

Single molecules of terrylene in di-substituted naphthalenes crystallizing in the herringbone pattern

“…Electronic states and spectra of Tr molecules were already subject of several quantum-chemistry studies. [24][25][26][27][28][29] In the present work we complemented our previous DFT B3LYP/6-31g(d,p) calculations performed for Tr in the ground S 0 state with the calculations for the excited S 1 state performed by TD DFT B3LYP/6-31g(d,p). Details of Tr geometry and vibrational frequencies in both states for isolated Tr were given in the ESI (Tables S2 and S3 †).…”

“…Franck-Condon principle predicts that the vibronic line should appear in the S 0 / S 1 spectrum if the projection of the geometry change between the initial and nal states onto the normal modes of the nal states follows displacement vectors of the vibration. 30 A good example is $247 cm À1 (a g ) vibration in isolated Tr, in which the displacement vectors point along the long axis of the molecule, 27,29 and the transition between the electronic S 0 and S 1 states is connected with the shortening of the bond lengths between the central and the external naphthalene moieties 25 (see the structures presented in Table S5 of the ESI †).…”