The Effect of Acceptor Structure on Emission Color Tuning in Organic Semiconductors with D–π–A–π–D Structures

A series of novel donor–acceptor D–π–A–π–D compounds were synthesized and characterized in order to determine the influence of different acceptor units on their properties. The introduction of acceptor moieties had a direct impact on the HOMO and LUMO energy levels. Fluorescence spectra of compounds can be changed by the choice of an appropriate acceptor and were shifted from the green to the near-infrared part of spectra. Due to observed concentration induced emission quenching, the green exciplex type host was used to evaluate the potential of synthesized molecules as emitters in organic light emitting diodes (OLEDs)

Electrochromic Properties of Novel Selenophene and Tellurophene Derivatives Based on Carbazole and Triphenylamine Core

The 2,7- and 3,6-substituted carbazole and triphenylamine chalcogenophene (Se, Te) derivatives and their electrodeposited polymers are investigated using electrochemical and UV–vis–NIR/ESR spectroelectrochemical methods. Major differences in the case of oxidation and electropolymerization behavior between monomers and related polymers are shown. Se and Te atoms do not conjugate their lone electron pairs with the π-conjugated system and therefore only increase the contribution of the quinoid form of the chalcogenophene unit. The 2,7- substituted carbazole derivatives present stronger carbazole–chalcogenophene conjugation than 3,6-substituted derivatives. One 3,6-substituted carbazole derivative and triphenylamine derived polymers were found to have promising electrochromic properties with black electrochromism

Thermally Activated Delayed Fluorescence with Narrow Emission Spectrum and Organic Room Temperature Phosphorescence by Controlling Spin-Orbit Coupling and Phosphorescence Lifetime of Metal-Free Organic Molecules

This work shows a study of two organic molecules with very similar, large singlet-triplet gap of which one is a TADF emitter and the other an RTP emitter. By investigation of photophysical properties of these compounds, it is possible to explain their distinct behavior. Properties are studied in non-polar polymer and OLED host with further device fabrication. Furthermore, this work presents a CT TADF emitter that shows narrow and resolved electroluminescence (FWHM of 53 nm). The study presents efficient RTP emitter based on the D-D-D structure and also a first acridone-based TADF emitter of D-A-D structure

Electrochemically deposited poly(selenophene)-fullerene photoactive layer: Tuning of the spectroscopic properties towards visible light-driven generation of singlet oxygen

A selenophene-containing fullerene dyad (C60Se) was electrochemically co-deposited with bis-selenophene (BisSe) to form a visible light absorbing poly(selenophene) layer with incorporated fullerene photosensitizers on platinum (Pt) or indium-tin oxide (ITO) substrates. The resulting photoactive films (P(C60Se_BisSe)) were characterized by cyclic voltammetry, UV–Vis, IR, Raman and X-ray photoelectron spectroscopies. The efficiency of P(C60Se_BisSe) towards singlet oxygen photogeneration was investigated by applying reactions with chemical traps, i.e. α-terpinene and 1,3–diphenylisobenzofuran (DPBF), monitored by UV–Vis spectroscopy. The composition of the electropolymerized layer was controlled by varying the monomers ratio in the feed solution and it had a strong influence on the spectroscopic and photosensitizing properties of the deposited film. It has been shown that the efficiency of the visible light-driven singlet oxygen generation can be increased by optimizing the ratio between C60 photosensitizers and organic units in the layer

Thermally Activated Delayed Fluorescence Mediated through the Upper Triplet State Manifold in Non-Charge-Transfer Star-Shaped Triphenylamine–Carbazole Molecules

Thermally activated delayed fluorescence has been found in a group of tricarbazolylamines that are purely electron-donating, non-charge-transfer (CT) molecules. We show that the reverse intersystem crossing step in these materials is mediated through upper triplet states. Reverse internal conversion is shown to be the thermally activated mechanism behind the triplet harvesting mechanism. The strongly mixed n−π*/π–π* character of the lowest energy optical transitions retains high oscillator strength and gives rise to high ΦPL. Organic light-emitting diode devices using these materials were fabricated to show very narrow (full width at half-maximum = 38–41 nm) electroluminescence spectra, clearly demonstrating the excitonic nature of the excited states. This new combination of physicochemical properties of a non-CT molecule yields thermally activated delayed fluorescence, but via a different, physical mechanism, reverse internal conversion delayed fluorescence

Observation of Dual Room Temperature Fluorescence-Phosphorescence in Air, in the Crystal Form of a Thianthrene Derivative

Thianthrenes have been nearly forgotten as phosphors in recent years, but are now coming back, showing their strong potential in luminescent applications. Here, we present a comprehensive photophysical study of a carbazolyl derivative of thianthrene in different matrices and environments. The diffusion of oxygen is slowed down in the rigid environment of thianthrene organic crystals suppressing their phosphorescence quenching, as well as triplet-triplet annihilation. This facilitates the observation of simultaneous fluorescence and phosphorescence emissions at room temperature, in air, giving origin to strong white luminescence. Moreover, the color coordinates of the dual fluorescence-phosphorescence white emission, which is observed only in rigid amorphous media and in crystals, can be tuned