A Review on the Emitting Species in Conjugated Polymers for Photo‐ and Electro‐luminescence

Abstract

In conjugated polymers, fluorescence from a single polymer chain, which is contrasted with measurements on an ensemble or bulk collection of molecules, can provide important information about conformation of single polymer chain and energy transfer between different conjugation length segments within single polymer chain. On the other hand, the presence of intrachain or interchain interactions plays an important role on their photoluminescence (PL) and electroluminescence (EL) properties. In addition to non-interacting isolated chain, there are five interacting emitting species, namely: photo-excited dimers including excimer and exciplex, electrical-excited dimers including electromer and electroplex, and aggregate. Excimer, exciplex, and aggregate can lead to a generation of new peak with featureless structure on the longer wavelength side in the fluorescence spectrum and usually cause a lowering in PL quantum efficiency. These three emitting species can be observed in both PL and EL spectra. In addition, electromer and electroplex only appear in EL spectrum but not in PL spectrum. The presence of electromer and electroplex also leads to a new peak at longer wavelength side. Another non-interacting ground-state emitting species, b phase, consists of a chain segment with a more coplanar conformation and therefore results in a longer conjugation and clear vibronic transitions.

Star-branched cationic light-emitting dot with silsesquioxane core, synthesis, and light scattering studies

“…M exhibits non-aggregative characteristics leading to identical emission in solid state and in solution as PL spectra of film does not red-shift from that of dilute solution. The hydrophilic star-like emitting dot W is highly water-soluble and the emissive wavelength is stable over a wide range of pH (3)(4)(5)(6)(7)(8)(9)(10)(11). The UV and PL wavelengths of W in aqueous solution remain unchanged when the concentration of polymer changes.…”

“…However, aggregation caused by intermolecule and intramolecule aromatic p-p stacking commonly exist in 1D chain-like and 2D disk-like polyelectrolyte [2], which adversely reduces the quantum efficiency of light-emitting applications due to the increase in non-radiative emission. Aggregation also results in unstable luminescence, e.g., red-shifted emission from solutions of different concentration [3]. Polyelectrolyte solution is rather complicated due to the strong long-range electrostatic interactions and the dissociation of polyelectrolyte into numerous counter ions and polyions.…”

Bipolar and Unipolar Silylene-Diphenylene σ-π Conjugated Polymer Route for Highly Efficient Electrophosphorescence

“…The side arm isolated moieties TPA (3.07 eV) and OXD (2.98 eV) can efficiently transfer their E T to silylene-diphenylene backbone (referred to 2.67 eV of Si(dBu)), and the TPA-OXD exciplex forms upon photoexcitation in which one component of the pair is originally in the photo-excited state and the other is in the ground state. Thus, it is forbidden for directly energy transfer from the side arm moieties to TPA-OXD exciplex (2.42 eV) since the exciplex exists only under excitation but is dissociative in the ground state2728. As the system doped with the green phosphor (2.40 eV), the silylene-diphenylene backbone and TPA-OXD exciplex can transfer their triplet energies to the phosphor.…”

Plasmonic-enhanced fluorescent conjugated polymer chemosensor for ultra-sensitive detection of nitroaromatic vapors

“…Excitation sources include chemical reactions [30,31], electrical (i.e. current) sources [32][33][34][35][36], mechanical stresses and forces [37], thermal [38], as well as incident photons [34,39]. Molecular excitation by chemical reactions produces chemiluminescence, as in the reaction of iron with luminol in forensic blood detection assays as well as bis-(2,4,5-trichloro-6-carbopentoxyphenyl) oxalate (CPPO) reaction with hydrogen peroxide in glow sticks [40].…”

“…Chemiluminescence occurring within living organisms is further classified as bioluminescence [41,42], the most prominent example thereof being the luciferase-mediated oxidation of luciferin as evinced by Lampyridae fireflies and others [43]. Photoluminescence (PL) is the form of luminescence whereby light is emitted from a molecule after absorption of a photon [34,39]. PL is broken down into two further classes based on the nature of the excited state:…”