Excited-State and Photoelectrochemical Behavior of Pyrene-Linked Phenyleneethynylene Oligomer
ABSTRACT An oligophenyleneethynylene (OPE), 1,4-bis(phenyleneethynyl)-2,5-bis(hexyloxy)benzene (2), is coupled with pyrene to extend the conjugation and allow its use as a light-harvesting molecule [Py-OPE (1)]. The absorption and emission maxima of 1 are red-shifted compared to those of 2. Similar differences in the singlet and triplet excited-state properties are evident. The fluorescence yield of 2 in toluene is 0.53, which is slightly less than the value for the parent OPE (2) of 0.66. The excited singlet and triplet of 1 as characterized from transient absorption spectroscopy exhibit lifetimes of 1.07 ns and 4.0 micros, respectively, in toluene. When 1 was cast as a film on a glass electrode (OTE) and excited with a 387-nm laser pulse, we observed the formation of excitons that decayed within a few picoseconds. When 1 was cast as a film on a SnO2-modified conducting glass electrode (OTE/SnO2), a small fraction of excitons dissociated to produce a long-lived charge-separated state. The role of the SnO2 interface in promoting charge separation was inferred from the photoelectrochemical measurements. Under visible light excitation, the OTE/SnO2 electrode was capable of generating photocurrent (approximately 0.25 mA/cm2) with an incident photon conversion efficiency (IPCE) of approximately 6%.
SourceAvailable from: Maurizio Munizmiranda[Show abstract] [Hide abstract]
ABSTRACT: Two series of 2,5-di(alkoxy)phenyleneethynylene oligomers were synthesized by Sonogashira–Heck coupling reaction. The chemical structure was corroborated by 1H, 13C, APT, DEPT-135 NMR, Raman, FTIR and MALDI-TOF mass spectrometry. The chemical structure of the molecules has been varied in order to study the effect on the physicochemical and optoelectronic properties of the different chain lengths of the lateral substituents (dodecanoxy and butoxy), of different terminal groups (H, Br and I), of different chain length (3, 5 and 7 repeat units in the main conjugated backbone). The thermal properties were analyzed by DSC, TGA and by temperature-dependent X-ray diffraction. The diffraction studies of the oligomers revealed a crystalline behavior for the butoxy series, while for the dodecanoxy series the X-ray patterns are consistent with a supramolecular organization formed of randomly distributed crystalline domains that exhibit a periodic structure at small angles, indicating the presence of a lamellar order. The optical properties can be modulated within a series by increasing the length of the conjugated oligomer chain. On the contrary, neither the length of the alkoxy substituents nor the terminal groups have effect on the shape of the absorption and emission spectra.Journal of Molecular Structure 11/2009; 936:177. DOI:10.1016/j.molstruc.2009.07.036 · 1.60 Impact Factor
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ABSTRACT: In order to give an insight of the special spectra of isolated π systems, a series of pyrene–fluorene derivatives, with conjugated or non-conjugated pyrene groups, were systematically studied. Besides absorption of non-conjugated pyrene itself and main conjugation chain, all the pyrene-non-conjugated large conjugated materials show a characteristic sharp absorption peak at ∼352 nm. Through systematical investigation, this special absorption peak was attributed to the intramolecular through-space interaction between the two isolated large π systems. Such interaction could also be defined as π – π hyperconjugation. And from quantum calculation, this intramolecular interaction does shorten the length of single bond. Through systematical research, the condition of this intramolecular through-space interaction is proved to be that the non-conjugated pyrene must have projection on fluorene plane. And then this effect is applied to explain the improved injection ability of the materials by bringing out one simple hopping model.Organic Electronics 03/2013; 14(3):782–789. DOI:10.1016/j.orgel.2012.12.035 · 3.68 Impact Factor
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ABSTRACT: The synthesis of a 2,5-bis(dodecanoxy)phenyleneethynylene-butadiyne series with 2, 4, 6 and 8 phenyl rings is reported. Sonogashira coupling reaction, rather than the Glaser/Eglinton/Hay reactions classically used for butadiyne formation was applied. The molecular structures of all compounds were confirmed by 1H, DEPT-135, APT 13C, MALDI-TOF, FTIR and FT-Raman analyses. The linear and nonlinear optical properties were studied in solution by UV/Vis, static and time-resolved fluorescence, and by two-photon absorption (2PA) spectroscopy. With the exception of the dimer, for which intersystem crossing is very favoured due to the low energy gap between the singlet and triplet states as theoretically predicted, the other oligomers present high fluorescence quantum yields (0.77–0.82) and large cross-sections (up to 5000 GM for the octamer) that could be applied in multiphoton microscopy or nonlinear optics.European Journal of Organic Chemistry 08/2013; 2013(24). DOI:10.1002/ejoc.201300230 · 3.15 Impact Factor