  Dibenzoterrylene (DBT) has garnered interest as a potential single photon
source (SPS). To have a better grasp of any possible limitations of using DBT
for this application, a better understanding of its optical properties is
needed. We use a configuration interaction (CI) strategy to calculate the many
body wavefunctions of DBT, and we use these wavefunctions to calculate its
optical properties. We calculate the linear absorption spectrum and the spatial
distributions of electrons involved in several bright transitions. We also
calculate the two-photon absorption spectrum of DBT and show that there are
several excited states that are bright due to two-photon absorption. Except at
high photon energies, we predict that there are no competing optical processes
regarding the use of DBT as a SPS. Our calculations provide details of the
optical properties of DBT that are interesting in general, and useful for
considering optical applications of DBT.
