We report Förster resonant energy transfer (FRET) with a Förster radius R 0 of 4.8 nm and exciplex formation in composites containing two functionalized anthradithiophene (ADT) derivatives, ADT-TES-F (donor, D) and ADT-TIPS-CN (acceptor, A) depending on the D−A distance. In composites containing bulk D/A heterojunctions, exciplex photoluminescence (PL) emission peaked at ∼668 nm dominated the PL spectra. The exciplex contributed to charge carrier photogeneration on nanosecond time scales in composites, in contrast to sub-500 ps carrier photogeneration observed in ADT-TES-F pristine films. Finally, significantly slower charge carrier recombination was obtained in composites, as compared to that of pristine ADT-TES-F films, due to electron trapping at the ADT-TIPS-CN enabling the hole to propagate in the ADT-TES-F host.

We quantify guest molecule aggregation and its effect on the photoconductive properties of guest-host thin films, depending on the guest concentration and host material. A high-performance anthradithiophene ͑ADT͒ derivative served as a guest, while functionalized benzothiophene ͑BTBTB͒ and polymethylmethacrylate ͑PMMA͒ were chosen as hosts. Aggregates exhibited redshifted optical absorption and photoluminescence ͑PL͒ spectra, as well as reduced PL quantum yields. Propensity toward guest aggregation differed for PMMA and BTBTB hosts. Photocurrents dramatically increased as the percentage of aggregated guest molecules increased due to considerably higher charge carrier mobility in the aggregates. At low guest concentrations, BTBTB films outperformed PMMA films.

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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 cm 2 /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.