3,6,9,12-Tetrasubstituted Chrysenes: Synthesis, Photophysical Properties, and Application as Blue Fluorescent OLED

A short synthesis of unsubstituted chrysene is described to provide a cheap source of this compound. This chrysene was used to prepare 3,6,9,12-tetrabromochrysene, which was subsequently transformed into various 3,6,9,12-tetrasubstituted chrysenes bearing four aryl, alkynyl, or amino groups by means of the Suzuki, Sonogashira, or Buchwald–Hartwig coupling reaction, respectively. These substituents result in large bathochromic shifts in the chrysene absorption and emission spectra. These new chrysene derivatives show blue fluorescent emission (401–471 nm) with high quantum yields (0.44–0.87). DFT calculations on these chrysenes rationalize well the substituent effects on their HOMO and LUMO energy levels. One representative chrysene (<b>6g</b>) was used as a blue fluorescent emitter in an OLED device that showed an outstanding external quantum efficiency (η = 6.31%) with blue emission [CIE (<i>x</i>, <i>y</i>) = (0.13, 0.20)] and a low turn-on voltage (3.0 V)

3,6,9,12-Tetrasubstituted Chrysenes: Synthesis, Photophysical Properties, and Application as Blue Fluorescent OLED

A short synthesis of unsubstituted chrysene is described to provide a cheap source of this compound. This chrysene was used to prepare 3,6,9,12-tetrabromochrysene, which was subsequently transformed into various 3,6,9,12-tetrasubstituted chrysenes bearing four aryl, alkynyl, or amino groups by means of the Suzuki, Sonogashira, or Buchwald–Hartwig coupling reaction, respectively. These substituents result in large bathochromic shifts in the chrysene absorption and emission spectra. These new chrysene derivatives show blue fluorescent emission (401–471 nm) with high quantum yields (0.44–0.87). DFT calculations on these chrysenes rationalize well the substituent effects on their HOMO and LUMO energy levels. One representative chrysene (<b>6g</b>) was used as a blue fluorescent emitter in an OLED device that showed an outstanding external quantum efficiency (η = 6.31%) with blue emission [CIE (<i>x</i>, <i>y</i>) = (0.13, 0.20)] and a low turn-on voltage (3.0 V)

New Iridium Dopants for White Phosphorescent Devices: Enhancement of Efficiency and Color Stability by an Energy-Harvesting Layer

A new light blue complex (fmoppy)₂Ir­(tfpypz) [bis­(4′-fluoro-6′-methoxylphenyl pyridinato)-iridium­(III)-3-(trifluoromethyl)-5-(pyridin-2-yl)-1,2,4-triazolate] and a new orange complex (dpiq)₂Ir­(acac) [bis­(3,4-diphenylisoquinoline)-iridium­(III)-acetylacetonate] were synthesized. These two complexes were used as the dopants for the fabrication of two-element white phosphorescent devices. Via the introduction of a thin energy-harvesting layer (EHL) to harvest the extra energy and exciton from the emission zone, highly efficient two-element white devices with excellent color stability were created. One of the best devices shows yellow-white color emission with an extremely high external quantum efficiency (EQE) of 21.5% and a current efficiency of 68.8 cd/A. The other device gave a pure white emission with an external quantum efficiency of 19.2% and a current efficiency of 53.2 cd/A. At a high brightness of 1000 cd/m², the EQE still remains as high as 18.9 and 17.2%. With a brightness of 1000–10000 cd/m², the CIE coordinates of these two devices shift by only (0.02, ≤0.01). The white phosphorescent devices with the EHL showed much higher efficiency and better color stability than the one without the EHL

Hybrid Porous Polymers Combination of Octavinylsilsesquioxane/Pyrene with Benzothiadiazole Units for Robust Energy Storage and Efficient Photocatalytic Hydrogen Production from Water

We investigated the performance that is improved in various applications through molecular structural alterations. Specifically, we emphasized the importance of controlling the branching densities of organic moieties as a useful tactic for varying the surface area and porosity of hybrid porous organic/inorganic polymers (HPPs), which include octavinylsilsesquioxane (OVS) units. This study shows that adjusting the branching densities could greatly enhance energy storage and hydrogen production. The two-branched chemical structure (4,7-dibromo-2,1,3-benzothiadiazole, BT-Br2) and the four-branched organic compound (1,1,2,2-tetrakis(4-bromophenyl)ethylene, TPE-Br4) are individually reacted with OVS and 1,3,6,8-tetrabromopyrene (Py-Br4) twice to prepare the HPPs. These materials with high or low cross-linking density, as well as small and large surface areas, are synthesized by this dual reaction, which also produces HPPs with different cross-linking densities. Based on Brunauer–Emmett–Teller calculations, the OVS-Py-BT HPP has more than 4.5 times larger surface area than the OVS-Py-TPE HPP material. Remarkably, OVS-Py-BT HPP exhibited exceptional results for supercapacitor applications, with specific capacitance values of 248 and 54 F/g for OVS-Py-BT and OVS-Py-TPE HPPs, respectively, as determined by galvanostatic charge–discharge. OVS-Py-BT HPP significantly outperformed OVS-Py-TPE HPP in photocatalytic hydrogen evolution. This is evident from their respective hydrogen evolution rates: 1348 μmol g–1 h–1 for OVS-Py-BT HPP and a much lower 11.3 μmol g–1 h–1 for OVS-Py-TPE HPP

Design and Synthesis of Cycloplatinated Polymer Dots as Photocatalysts for Visible-Light-Driven Hydrogen Evolution

By mimicking natural photosynthesis, generating hydrogen through visible-light-driven splitting of water would be an almost ideal process for converting abundant solar energy into a usable fuel in an environmentally friendly and high-energy-density manner. In a search for efficient photocatalysts that mimic such a function, here we describe a series of cycloplatinated polymer dots (Pdots), in which the platinum complex unit is presynthesized as a comonomer and then covalently linked to a conjugated polymer backbone through Suzuki–Miyaura cross-coupling polymerization. On the basis of our design strategy, the hydrogen evolution rate (HER) of the cycloplatinated Pdots can be enhanced by 12 times in comparison to that of pristine Pdots under otherwise identical conditions. In comparison to the Pt-complex-blended counterpart Pdots, the HER of cycloplatinated Pdots is over 2 times higher than that of physically blended Pdots. Furthermore, enhancement of the photocatalytic reaction time with high eventual hydrogen production and low efficiency rolloff are observed by utilizing the cycloplatinated Pdots as photocatalysts. On the basis of their performance, our cyclometallic Pdot systems appear to be alternative types of promising photocatalysts for visible-light-driven hydrogen evolution

Partially-Screened Field Effect and Selective Carrier Injection at Organic Semiconductor/Graphene Heterointerface

Due to the lack of a bandgap, applications of graphene require special device structures and engineering strategies to enable semiconducting characteristics at room temperature. To this end, graphene-based vertical field-effect transistors (VFETs) are emerging as one of the most promising candidates. Previous work attributed the current modulation primarily to gate-modulated graphene–semiconductor Schottky barrier. Here, we report the first experimental evidence that the partially screened field effect and selective carrier injection through graphene dominate the electronic transport at the organic semiconductor/graphene heterointerface. The new mechanistic insight allows us to rationally design graphene VFETs. Flexible organic/graphene VFETs with bending radius <1 mm and the output current per unit layout area equivalent to that of the best oxide planar FETs can be achieved. We suggest driving organic light emitting diodes with such VFETs as a promising application