Figure 5

The \(\theta = 90^\circ\) field-swept prompt EPR quintet spectrum for a parallel dimer of pentacene molecules in a dilute crystal. (a) The energies of diabatic quintet states as a function of the Zeeman field. Parameters used are literature values for parallel pentacene molecules in p-terphenyl¹⁴. The experiments performed in Ref.¹⁴ are in the strong field limit, where the transitions are far removed from the avoided crossings between adiabatic states (b). In this limit, the diabatic states (solid lines) of the Zeeman hamiltonian are very close to the adiabatic states (dashed lines). Open circles indicate computed transitions which compare favorably to the field values of transitions reported by Ref.¹⁴ (closed circles). With \(B_0||x'\), the \(^1TT\) state transfers only to the quintet \(M=0,\pm 2\) states. Wavy arrows indicate the direction of transitions for \(D>0\). (c) Simulated prompt EPR spectrum, where positive changes in the intensity indicate induced absorption and negative changes indicate stimulated emission. The relative peak intensities were calculated from coupling matrix elements between the singlet and quintet states using a short-time approximation to the Pauli master equation. These populations reproduce the AEAE polarization pattern for the quintet part of the spectrum reported in Ref.¹⁴.