We present optical, photoluminescent (PL), and photoconductive properties of functionalized anthradithiophene
(ADT) and benzothiophene (BTBTB) derivatives and their composites. Solution-deposited ADT films exhibit
charge carrier mobilities of over 1.5 cm2/Vs, high PL quantum yields, and high photoconductivity at room
temperature. We show molecular arrangement and intermolecular interactions significantly contribute to the
(opto)electronic properties of thin films of these pi-stacked materials. In addition, these properties can be
effectively manipulated through the addition of guest molecules to a host material. In particular, exciton and
charge carrier dynamics can be varied using a competition between photoinduced charge and energy transfer
in a guest-host system. To better understand these processes at a molecular level, we apply single-molecule
fluorescence spectroscopy (SMFS) to probe the effects of intermolecular interactions on the molecular properties.
Specifically, we demonstrate that ADT molecules exhibit high enough quantum yields and photostability to be
imaged on a single-molecule level at room temperature. Moreover, we show that stability of single ADT molecules
immobilized in a solid-state matrix are comparable to those of the best fluorophores utilized in SMFS.