We present optical, photoluminescent (PL), and photoconductive properties of functionalized anthradithiophene
(ADT) 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. We show that molecular arrangement
and intermolecular interactions significantly contribute to (opto)electronic properties of guest-host thin films
of these pi-stacked materials. Specifically, the formation of aggregates plays an important role in establishing
efficient conduction pathways in ADT derivatives dispersed in a host matrix. In addition, the extent and nature
of aggregation and the resulting changes in PL and photoconductive behavior can be effectively manipulated
through different film fabrications techniques. Furthermore, energy transfer and exciplex formation has been
shown to occur between two different ADT derivatives, which also alters the photoconductive response of the
systems. We explore the dependence of the photoconductive response of such guest-host systems on excitation
wavelength.
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.
The optical, fluorescent, and photoconductive properties of
solution-processable functionalized pentacene and
anthradithiophene (ADT) derivatives are presented. Considerable fluorescence quantum yields of - 70-75% and ~ 40-50% were observed in several ADT derivatives in toluene solutions and in thin films, respectively. Using
conventional wide-field fluorescence microscopy, ADT derivatives were successfully imaged in the polymethylmethacrylate
(PMMA) matrix on a single molecule level, at 532 nm at room temperature. All films exhibited fast
charge carrier photogeneration upon 100 fs 400 nm excitation and power-law decay dynamics of the transient
photocurrent over many orders of magnitude in time. In
solution-deposited ADT thin films, effective charge
carrier mobilities calculated from the space-charge-limited currents reached ~ 0.1 cm2/Vs. In the same films,
bulk photoconductive gains of up to 130 were observed at 532 nm continuous wave (cw) excitation with light
intensity of 0.58 mW/cm2 at the applied electric field of 4 × 104 V/cm. Effects of metal-organic interfaces on
the dark current and transient and cw photocurrent are also discussed.
We report on the effects of introducing guest molecules into a functionalized anthradithiophene (ADT) host
on the photoluminescent (PL) and photoconductive properties of solution-deposited thin films. An addition
of 0.1 wt % of an ADT derivative with cyano end groups (ADT-TIPS-CN) to a fluorinated ADT derivative
(ADT-TES-F) resulted in the near complete quenching of the fluorescence spectrum of the ADT-TES-F host
with an enhancement in the fluorescence spectrum of the ADT-TIPS-CN guest. A markedly longer PL lifetime
was noted in films containing 10% ADT-TIPS-CN guest molecules compared to both pristine ADT-TES-F and
ADT-TIPS-CN films. Stronger temperature dependence of the PL quantum yield was obtained in ADT-TIPSCN/
ADT-TES-F films at low ADT-TIPS-CN concentrations than in films of pristine material, with PL decreasing
with increasing temperature. Significant changes in the photoexcited charge carrier dynamics were observed on
nanosecond time-scales after 400 nm 100 fs pulsed photoexcitation upon adding ADT-TIPS-CN guest molecules
to the ADT-TES-F host. In contrast, no considerable change in the photocurrent was detected under continuous
wave 532 nm excitation for guest molecule concetrations up to 1% of ADT-TIPS-CN in ADT-TES-F.
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