We are reporting the optical study of two types of poly (3-thienylene vinylene) (PTV) derivatives with linear and bulk side chain configurations. The first one, poly(3-dodecylthienylenevinylene) with controlled regioregularity (PTV-CR) with an alkyl side group, showed a high degree of crystallinity, whereas the second one, imide-PTV with an electron deficient imide side group, is amorphous. Continuous wave-photoinduced absorption revealed different features of the long-lived triplet absorptions, with the geminately generated triplet–triplet pair in imide-PTV bearing more intrachain characteristics with fast recombination kinetics (<10 μs). On the other hand, the isolated triplet in PTV-CR generated by intersystem crossing had more interchain characteristics with slow recombination kinetics (ms). The decay of the triplet–triplet pair in imide-PTV is monomolecular even at a high pump intensity of 240 mW/cm2, whereas the isolated triplets in PTV-CR recombine bimolecularly at a very low pump intensity of 10 mW/cm2. Grazing incidence X-ray diffraction, doping induced absorption, and various dependences of the photoinduced absorption spectrum have corroborated the finding that reduced interchain interaction favors the formation of a correlated triplet–triplet pair, a precursor to two independent triplets formed via fission.
We report on the photophysical properties of a soluble thienylene-vinylene π-conjugated polymer, namely imide poly-thienylene vinylene. Ultrafast pump probe spectroscopy reveals that a broad photoinduced absorption (PA) band is immediately photogenerated along with a narrower PA from the photoinduced singlet excitons. The broad PA is susceptible to magnetic field and thus is assigned to a correlated triple pair state. This feature shows a long lifetime persisting into the μs time domain, in contrast to the singlet exciton PA, which quickly decays on a 10-ps timescale. The steady-state PA spectrum is identical to the transient PA spectrum of the triplet pair state but shows a magnetic field response that is typical to isolated triplet excitons.
We report the development of a fully regioregular Poly(3-Dodecyl-2,5-thienylenevinylene)
(HT-HT PDDTV) using the Horner-Emmons reaction, and studies using proton and carbon
NMR spectroscopy, UV-vis absorption spectroscopy, fluorescence spectroscopy,
cyclovoltametry, thermal analysis (DSC & TGA) and XRD. The HT-HT PDDTV developed has
practically no solubility in boiling hexane, in sharp contrast to the literature PDDTV prepared
from the Stille coupling reaction, which is mostly soluble in hexanes (an indication of high
content of structural defects). The optical energy gaps are 1.80 eV in chloroform solution and
1.65 eV in film. The HOMO/LUMO of the film were -5.03 eV and
-3.63eV, respectively. The
electrochemical energy gap in the film is 1.4 eV. XRD study shows that a decent crystalline
structure was formed without any annealing of the as-cast films. The lamellar sheets (formed
from π. π. stacking) preferentially are oriented in parallel to the substrate surface with an
interlayer spacing of 17.6 angstrom.
We report a novel type of nanocomposite of conjugated polymer (regio-regular polythiophene) with infrared-sensitive, PbSe quantum dots (QD), which have size-tunable lowest-energy absorption bands between 0.3 and 1 eV. Thin film devices show very good diode characteristics and sizable photovoltaic response with an open circuit voltage, Voc, of ~ 0.3-0.4 V and short circuit current density, Jsc, of ~ 0.2mA/cm2, which is significantly higher than recently reported in PbS QD-based devices. This is the evidence of a quite efficient photoinduced charge transfer between the polymer and QD, with infrared sensitivity. Photocurrent under reverse bias is significantly enhanced to Jph ~ 1 mA/cm2 indicating that the polythiophene/PbSe QD system can be used as effective infrared photodetectors. Detailed spectroscopic studies of photoresponse over a wide spectral range are presented. Quenching of photoluminescence by PbSe QDs has also been studied to gain more understanding of energy and charge transfer in this system.