We report detailed temperature dependent photoluminescence (PL) spectra of pentacene (PEN), perfluoropentacene (PFP), and PEN:PFP mixed thin films grown on SiO2. PEN and PFP are particularly suitable for this study, since they are structurally compatible for good intermixing and form a model donor/acceptor system. The PL spectra of PEN are discussed in the context of existing literature and compared to the new findings for PFP. We analyze the optical transitions observed in the spectra of PEN and PFP using time-dependent density functional theory (TD-DFT) calculations. Importantly, for the mixed PEN:PFP film we observe an optical transition in PL at 1.4 eV providing evidence for coupling effects in the blend. We discuss a possible charge-transfer (CT) and provide a tentative scheme of the optical transitions in the blended films.

We present optical absorption spectra of mixed films of pentacene (PEN) and perfluoropentacene (PFP) grown on SiO 2 . We investigated the influence of intermolecular coupling between PEN and PFP on the optical spectra by analyzing samples with five different mixing ratios of PFP:PEN with variable angle spectroscopic ellipsometry and differential reflectance spectroscopy. The data show how the spectral shape is influenced by changes in the volume ratio of the two components. By comparison with the pure film spectra an attempt is made to distinguish transitions due to intermolecular coupling between PEN and PFP from transitions caused by interactions of PEN (PFP) with other molecules of the same type. We observe a new transition at 1.6 eV which is not found in the pure film spectra and which we assign to the coupling of PFP and PEN.

We present the optical properties of fully (C 42 F 28 , PF-RUB) and half-fluorinated (C 42 F 14 H 14 ; F 14-RUB) rubrene, both in thin films and as monomers in solution and compare them to hydrogenated rubrene (C 42 H 28 , RUB). All three compounds show similar optical absorption bands and photoluminescence line shapes. The results are interpreted with density functional calculations of the orbital energies and time-dependent density functional theory for the HOMO-LUMO transition. Red shifts induced by the surrounding solvent or organic thin films remain much smaller than for polyacenes, in keeping with previous observations for rubrene and existing models for the solvatochromic shifts. V

Thin films of fully and partially fluorinated rubrene deposited on Au(111) and Ag(111) were investigated using ultraviolet and X-ray photoelectron spectroscopy. We demonstrate that fluorination of the molecules is an efficient way for tuning the metal−organic interface dipole and the hole injection barrier. Moreover, the results indicate that the pronounced electrostatic dipole moment of partially fluorinated rubrene (F 14 -RUB) has a strong impact on the growth mode of these molecules. Most notably, we infer that the first layer of F 14 -RUB on Au(111) and Ag( 111) is formed by molecules with alternating orientation of their dipole moments whereas the second layer shows a nearly uniform orientation. Article pubs.acs.org/JPCC

We report on the oxidation potential of partially fluorinated (C42F14H14, F14-RUB) and perfluorinated rubrene (C42F28, PF-RUB) studied by cyclic voltammetry (CV) in solution as well as by spectroscopic ellipsometry and near edge X-ray absorption fine structure (NEXAFS) spectroscopy in thin films in combination with density functional theory computations. Due to their different electronic structure, the fluorinated derivatives have a higher oxidation potential and are more stable than rubrene (C42H28, RUB).