Photodegradation of Polyfluorene and Fluorene Oligomers with Alkyl and Aromatic Disubstitutions

Spatial Identification of "Zeroth Defect" Formation in Organic Light-Emitting Diodes by Multispectral Mappings

In recently developed organic semiconductors, the continuously improving sample purity makes the stability of the chemical bonds of organic materials themselves become a key factor in device stability, which provides greater uncertainty for the generation of "zeroth defect", and the spatial resolution of performance at different positions becomes particularly important. In this work, complete maps of electroluminescent, photoluminescent, and Raman scattering in the same area on an organic light-emitting diode during its operation have been achieved with a confocal spectrometer with multiple laser sources. The different spectral characters help to establish different regions and suggest the mechanism of degradation. In particular, Raman scattering has been shown to be very sensitive in a multilayer device to a change in thickness of several nanometers. In amorphous films with few defects, the very weak film uniformity, including the thickness and degree of aggregation, would induce dramatic degradation. The relatively thin and/or loosely textured region easily locally overheats and has the highest probability of "zeroth defect" generation. This method has high spatial resolution, a low level of damage to samples, good reproducibility, and multiple interconnected pieces of information, which is significant for online quality prediction and mechanistic analysis.

Effect of side chains on color purities of mono-triphenylamine-functionalized polyspirobifluorenes for pure blue polymer light-emitting diodes

Large and rigid substituents may facilitate the improvement of the color purity of polyfluorenes.

Tacticity effects in side-chain photoluminescent polymers

A significant red shift (or blue shift) can be observed by increasing the degree of isotacticity (or syndiotacticity).

Ultrabright Fluorescent Silica Nanoparticles Embedded with Conjugated Oligomers and Their Application in Latent Fingerprint Detection

Fluorescent micro- and nanosized particles have a broad range of applications in biology, medicine, and engineering. For these uses, the materials should have high emission efficiency and good photostability. However, many organic fluorophores suffer from aggregation-induced quenching effects and photobleaching. Here, we used a simple method based on covalently blending a fluorescent conjugated oligomer with silica nanoparticles to achieve emission quantum yields as high as 97%. The resulting system also showed excellent stability under continuous light illumination, in a range of pH values and temperatures, and in common solvents. This fluorescent material showed outstanding properties, including highly efficient blue emission, low cost, low toxicity, and easy synthesis. Furthermore, its effectiveness for latent fingerprint detection was demonstrated as a proof of concept on various substrates. The obtained emissive fingerprint powder gave good optical/fluorescent images with high contrast and resolution between the ridges and spaces.

Photochemical Degradation of Various Bridge-Substituted Fluorene-Based Materials

Photochemical degradation is an important issue to be overcome in advancing the lifetime of fluorene-containing conjugated polymers. In order to optimize the inertness of the materials, a quantitative measure for the efficiency of degradation is needed. Here, we introduce a method to measure a relative quantum yield of the photochemical degradation by monitoring the kinetics of the process by means of UV/vis spectroscopy and liquid chromatography (LC) techniques. This method is employed to a set of differently substituted 2,7-diphenylfluorenes, serving as model compounds for polyfluorene materials. Our measurements show that the quantum yield changes by orders of magnitude upon varying the bridge substituents and that altered kinetics indicate changing degradation mechanisms.

The effect of polymer solubilizing side-chains on solar cell stability

The impact of polymer side-chains on encapsulated OPV device stability is studied systematically in a series of low bandgap polymers.

Role of Nonemissive Quenchers for the Green Emission in Polyfluorene

The stability of fluorene-based compounds and polymers, especially at the bridged C-9 position under photoirradiation and thermal treatment, has claimed much attention. The emission of fluorenone formed by degradation of the 9-site is regarded as the origin of the low emission band at 2.2-2.3 eV in polyfluorene-based conjugated materials. We have investigated the role of nonemissive quenchers such as alkyl ketones, which were also one of the products of polyfluorene degradation, for the low-energy emission in polyfluorenes. The spectral characteristics of a blend system of polyfluorene/nonemissive quencher/fluorenone are found to accord well with the kinetics of actual polyfluorene degradation. Our results indicate that strong green emission in degraded polyfluorene would be not caused only by fluorenone, but also by nonemissive quenchers for their effectively quenching bulk emission.