Simultaneous ultrafast probing of intramolecular vibrations and photoinduced charge carriers in rubrene using broadband time-domain THz spectroscopy

We determine the ultrafast frequency- and time-resolved complex dielectric responses of photoexcited, single-crystal rubrene in the frequency range of 10–30 THz (330–1000 cm ^-1) using ultrafast broadband THz spectroscopy. In this frequency range, we observe the response of both photogenerated mobile charges and intramolecular vibrational modes simultaneously, both of which vary with time after excitation. The data in conjunction with a theoretical model indicate a dynamic blueshift of the 15.5 THz phonon.