Solvent and Temperature Effects on Spectral Properties of Two Poly （3-alkyl） thiophene Derivatives

Two alkyl substituted polythiophene derivatives : poly (3-hexylthiophene) ( P3 HT) and poly ( 3- decyhhiophene) (P3DT), have synthesized by oxidation coupling polymerization of 3-alkylthiophene using iron (Ⅲ) chloride as catalyst in chloroform. While both polymers in pure chloroform solution have maximum absorption at approximately same wavelength of 440 nm, they behave differently with respect to changes observed on their UV-visible and photoluminescence spectra when the quality of the poor solvent is changed in good solvent (chloroform) / poor solvent (methanol) mixtures. With increasing volume fraction of methanol in mixtures, the absorption spectra of P3HT and P3DT red-shift, peaking at maximum wavelength of 495 nm (P3HT) and 510 nm(P3DT). Furthermore, the absorption spectra of the two polymers in chloroform blueshift as the temperature rises. P3HT shows 4.73 nm blue-shifts at 50 ℃ in contrast to the case at 20 ℃, while P3DT blue-shifts about 5.04 nm. The photoluminescence spectra of the two polymers in mixed solution are also investigated, which show that the luminescence spectra shift to longer wavelength with an accompanying drop in the PL intensity as methanol is increased. The absorption and emission spectra of the two polymers in a poor solvent and a thin film are similar, which indicate that a similar longer conjugation length in the two cases. It could conclude that the polymers exist almost the same conformations and aggregations in both a poor solvent and a thin film. P3DT exhibits more sensitive spectra properties (big red-shifts in both absorption and luminescence spectra in poor solvents and large blue-shifts at high temperature) with contrast to P3HT, which imply that long side alkyl may improve the chromic properties of the polymer.     

Solvent and Temperature Effects on Spectral Properties of Two Poly(32alkyl)thiophene Derivatives

Two alkyl substituted polythiophene derivatives: poly(32hexylthiophene)(P3HT) and poly(32decylthiophene)(P3DT), have synthesized by oxidation coupling polymerization of 32alkylthiophene using iron (III) chloride as catalyst in chloroform. While both polymers in pure chloroform solution have maximum absorption at approximately same wavelength of 440 nm, they behave differently with respect to changes observed on their UV2visible and photoluminescence spectra when the quality of the poor solvent is changed in good solvent (chloroform) / poor solvent (methanol) mixtures. With increasing volume fraction of methanol in mixtures, the absorption spectra of P3HT and P3DT red2shift, peaking at maximum wavelength of 495 nm (P3HT) and 510 nm(P3DT). Furthermore, the absorption spectra of the two polymers in chloroform blue2shift as the temperature rises. P3HT shows 4.73 nm blue2shifts at 50℃in contrast to the case at 20℃, while P3DT blue2shifts about 5.04 nm. The photoluminescence spectra of the two polymers in mixed solution are also investigated, which show that the luminescence spectra shift to longer wavelength with an accompanying drop in the PL intensity as methanol is increased. The absorption and emission spectra of the two polymers in a poor solvent and a thin film are similar, which indicate that a similar longer conjugation length in the two cases. It could conclude that the polymers exist almost the same conformations and aggregations in both a poor solvent and a thin film. P3DT exhibits more sensitive spectra properties (big red2shifts in both absorption and luminescence spectra in poor solvents and large blue2shifts at high temperature) with contrast to P3HT, which imply that long side alkyl may improve the chromic properties of the polymer.     

Synthesis and characterizations of poly(3,6-thienophenanthrene) and poly(2,7-thienophenanthrene) and their applications in polymer light-emitting devices and solar cells

Here we report the synthesis of two novel phenylene-based polymers-poly(3,6-thienophenanthrene) (PTP36) and poly(2,7-thienophenanthrene) (PTP27) via base-free Suzuki–Miyaura reaction. The structure and electroluminescent properties of the meta-linked PTP36 and para-linked PTP27 are fully characterized. The obtained polymers were found to be liquid-crystalline, with broad band gap of 2.72 eV and 2.49 eV, respectively, which are much smaller than those of corresponding polyphenanthrenes. On the basis of PTP36 and PTP27, copolymers of 2,7-thienophenanthrene and 3,6-thienophenanthrene with 5,6-bis(octyloxy)-4,7-di(thiophen-2-yl)benzothiadiazole (DBT), namely PTP36-DBT and PTP27-DBT were prepared and be investigated as a potential donor material for polymer solar cells. The preliminary data show that the maximal power conversion efficiencies (PCEs) of the PTP27-DBT- and PTP36-DBT-based polymer solar cells are 3.5% and 0.9%, respectively.     

Exciton–Exciton Annihilation in Mixed‐Phase Polyfluorene Films

Singlet–singlet annihilation is studied in polyfluorene (PFO) films containing different fractions of β‐phase chains using time‐resolved fluorescence. On a timescale of >15 ps after excitation, the results are fitted well by a time‐independent annihilation rate, which indicates that annihilation is controlled by 3D exciton diffusion. A time‐dependent annihilation rate is observed during the first 15 ps in the glassy phase and in the β‐phase rich films, which can be explained by the slowdown of exciton diffusion after excitons reach low‐energy sites. The annihilation rate in the mixed‐phase films increases with increasing fraction of β‐phase present, indicating enhanced exciton diffusion. The observed trend agrees well with a model of fully dispersedβ‐phase chromophores in the surrounding glassy phase with the exciton diffusion described using the line‐dipole approximation for an exciton wavefunction extending over 2.5 nm. The results indicate that glassy andβ‐phase chromophores are intimately mixed rather than clustered or phase‐separated.     

Organic Bulk‐Heterojunction Photovoltaics Based on Alkyl Substituted Discotics

The photovoltaic behavior of three hexa‐peri‐hexabenzocoronene (HBC) derivatives has been investigated with respect to the influence of the alkyl side chains. Upon increasing the side chain length, the HBC chromophore becomes diluted, thus decreasing the amount of light absorbed. Differential scanning calorimetry and powder X‐ray analysis reveal that the HBC with the 2‐ethyl‐hexyl side chain is in a crystalline state at room temperature, while the other two HBCs containing 2‐hexyl‐decyl and 2‐decyl‐tetradecyl substituents in so‐called plastic crystalline state. The HBC with the shortest side chain is proven to be the best donor for perylenediimide, showing a highest external quantum efficiency of 12 %. Furthermore, scanning electron microscopy imaging suggested an important role of the morphology of the active film in determining the performance of the device.