Experimental reorganization energies of pentacene and perfluoropentacene: Effects of perfluorination

Abstract

Electron-phonon coupling of the highest occupied molecular orbital (HOMO) state is studied by high-resolution ultraviolet photoelectron spectroscopy (UPS) for pentacene (PEN) and perfluoropentacene (PFP) monolayers on graphite. The reorganization energy and related coupling constants associated with the interaction between holes and molecular vibrations are obtained experimentally using a single mode analysis (SMA) of the observed vibronic-satellite intensities of the monolayers. The results are compared with those estimated by multimode analyses of UPS spectra and those derived by means of theoretical approaches, indicating that the purely experimental method with SMA is useful for studying the reorganization energy and the hopping mobility of organic systems. Furthermore, we found that the reorganization energy of PFP is significantly greater than that of PEN, which is ascribed to the extended HOMO distribution of PFP by perfluorination of PEN. The comparison with the results derived from gas-phase UPS measurements is also discussed. © 2013 American Chemical Society.