An
ab initio
study of the effects of implicit and explicit hosts on the excited state properties of
pentacene and its nitrogen-based derivatives has been performed using ground state density func-
tional theory (DFT), time-dependent DFT and ∆SCF. We observe a significant solvatochromic
redshift in the excitation energy of the lowest singlet state (S
1
) of pentacene from inclusion in
a
p
-terphenyl host compared to vacuum; for an explicit host consisting of six nearest neighbour
p
-terphenyls, we obtain a redshift of 65 meV while a conductor-like polarisable continuum model
(CPCM) yields a 78 meV redshift. Comparison is made between the excitonic properties of pen-
tacene and four of its nitrogen-based analogues, 1,8-, 2,9-, 5,12-, and 6,13-diazapentacene with the
latter found to be the most distinct due to local distortions in the ground state electronic struc-
ture. We observe that a CPCM is insufficient to fully understand the impact of the host due to
the presence of a mild charge-transfer (CT) coupling between the chromophore and neighbouring
p
-terphenyls, a phenomenon which can only be captured using an explicit model. The strength
of this CT interaction increases as the nitrogens are brought closer to the central acene ring of
pentacene.