Charge carrier transport in perylene-based and pyrene-based columnar liquid crystals.

Electron and hole transport characteristics were evaluated for perylene-based and pyrene-based compounds using electron-only and hole-only devices. The perylene presented a columnar hexagonal liquid crystal phase at room temperature with strong molecular π-stacking inside the columns. The pyrene crystallizes bellow 166 °C, preserving the close-packed columnar rectangular structure of the mesophase.

Delayed Fluorescence by Triplet-Triplet Annihilation from Columnar Liquid Crystal Films.

Delayed fluorescence (DF) by triplet-triplet annihilation (TTA) is observed in solutions of a benzoperylene-imidoester mesogen that shows a hexagonal columnar mesophase at room temperature in the neat state. A similar benzoperylene-imide with a slightly smaller HOMO-LUMO gap, that also is hexagonal columnar liquid crystalline at room temperature, does not show DF in solution, and mixtures of the two mesogens show no DF in solution either, because of collisional quenching of the excited triplet states on the imidoester by the imide. In contrast, DF by TTA from the imide but not from the imidoester is observed in condensed films of such mixtures, even though neat films of either single material are not displaying DF.

Synthesis of 2,1,3-Benzoxadiazole Derivatives as New Fluorophores-Combined Experimental, Optical, Electro, and Theoretical Study.

Herein, we report the synthesis and characterization of fluorophores containing a 2,1,3-benzoxadiazole unit associated with a π-conjugated system (D-π-A-π-D). These new fluorophores in solution exhibited an absorption maximum at around ~419 nm (visible region), as expected for electronic transitions of the π-π type (ε ~2.7 × 10 L mol cm), and strong solvent-dependent fluorescence emission (Φ ~0.

High rectification in organic diodes based on liquid crystalline phthalocyanines.

The optical and electrical properties of mesogenic metal-free and metalated phthalocyanines (PCs) with a moderately sized and regioregular alkyl periphery were investigated. In solution, the individualized molecules show fluorescence lifetimes of 4-6 ns in THF. When deposited as solid thin films the materials exhibit significantly shorter fluorescence lifetimes with bi-exponential decay (1.

Polarized emission from stretched PPV films viewed at the molecular level.

We present a study on the photoluminescence (PL) of thin films of poly-(p-phenylene vinylene) (PPV), non-stretched and uniaxially stretched. The experimental study was carried out using linear polarized light as the excitation beam, oriented either parallel or perpendicular to the stretch axis (S). The results showed that when the excitation light source has polarization perpendicularly oriented to the stretch direction, the emitted PL presents maximum intensity in the orientation S, and a minimum in the direction orthogonal to S.

Exciton diffusion in polyfluorene copolymer thin films: kinetics, energy disorder and thermally assisted hopping.

A series of {(9,9-dioctylfluorene)(0.7-x)-(dibenzothiophene-S,S-dioxide)(0.3)-[4,7-bis(2-thienyl)-2,1,3-benzothiadiazole](x)} (PFS(30)-TBTx), where x represents the minor percentage of the red emitter 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT) randomly incorporated into the copolymer backbone, is investigated in order to follow the energy transfer from PFS(30) to TBT moieties.