Pentacene in 1,3,5-Tri(1-naphtyl)benzene: A Novel Standard for Transient EPR Spectroscopy at Room Temperature

Abstract

Testing and calibrating an experimental setup with standard samples is an essential aspect of scientifc research. Single crystals of pentacene in p-terphenyl are widely used for this purpose in transient electron paramagnetic resonance (EPR) spectros copy. However, this sample is not without downsides: the crystals need to be grown and the EPR transitions only appear at particular orientations of the crystal with respect to the external magnetic feld. An alternative host for pentacene is the glass forming 1,3,5-tri(1-naphtyl)benzene (TNB). Due to the high glass transition point of TNB, an amorphous glass containing randomly oriented pentacene molecules is obtained at room temperature. Here we demonstrate that pentacene dissolved in TNB gives a typical “powder-like” transient EPR spectrum of the triplet state fol lowing pulsed laser excitation. From the two-dimensional data set, it is straight forward to obtain the zero-feld splitting parameters and relative populations by spectral simulation as well as the B1 feld in the microwave resonator. Due to the simplicity of preparation, handling and stability, this system is ideal for adjusting the laser beam with respect to the microwave resonator and for introducing students to transient EPR spectroscopy.