Delocalized electronic excitations of pentacene dimers in a p-terphenyl host: picosecond photon echo experiments

Abstract

Photon echo evperlments are performed on delocabzed electromc evcltatlons of optxal dlmer states The delGuhzed dlmer states are found to have very long coherence times. close to the coherent hnxt The dlmer dephasmg IS quabtatlvely slmdar to dephasmg of pentacene monomers.

Temperature-dependent dephasing of delocalized dimer states of pentacene in p-terphenyl: picosecond photon echo experiments

“…The dimer absorptions are shifted from the monomer origin for two reasons [2]. First, the dipole-di- To the red, five pentacene dimer peaks are labeled R 1 through Rs.…”

“…The 01 and 02 origins coalesce into a broad and flat-topped peak because of the very high monomer concentration resulting in zero transmittance. To the red of the broad origins lie three well-resolved peaks, labeled R 3 , R4, and R5 ' which have previously been shown to arise from pentacene dimer states [2]. Several other less resolved peaks, labeled R 1 and R 2 , can also be observed on the side of the monomer absorption [2].…”

“…There has been an increasing amount of experimental and theoretical interest in dimer coherence in mixed crystals [1,2]. These dimers consist of isolated pairs of guest molecules substitutionally imbedded in a host crystalline lattice.…”

“…The first direct measurement of dimer coherence via photon echo experiments has recently been reported [2] for the system of pentacene dimers in a p·terphenyl host crystal. Only the coherence times for the dimer states shifted by intermolecular inter· actions to the red of the pentacene monomers (red dimer states) were measured.…”

“…In addition, an extensive temperature dependence of T2' (the dephasing time excluding the excited state to ground state lifetime contribution) of the red dimer state, R3 [2], is reported for the temperature range 1.3-16 K. Photon echo decay measurements provided T2' at low temperatures in which the homogeneous line is masked by inhomogeneous broadening.…”