Structure-property-function relationships of stabilized and persistent C- and N-based triaryl radicals

Structurally similar C- and N-based triaryl radicals are among the most commonly used structural motifs in stable, open-shell, organic molecules. The application of such species is associated with their stability, properties and structural design. This study summarizes the basic stabilization and persistence principles of C- and N-based triaryl radicals and highlights recent advances in design strategies of radicals tailored for specific applications.

Photophysical and semiconducting properties of isomeric triphenylimidazole derivatives with a benzophenone moiety

New isomeric compounds with imidazole and benzophenone moieties were synthesized and their thermal, photophysical, electrochemical and carrier mobilities have been analyzed.

Formation of a stable biradical triplet state cation versus a closed shell singlet state cation by oxidation of adducts of 3,6-dimethoxycarbazole and polychlorotriphenylmethyl radicals

We report an experimental and theoretical study of two stable radical adducts of the triphenylmethyl series, 1 and 2, whose composition and molecular structure are distinguished by the content and position of chlorine atoms in phenyls. The electrochemical study through cyclic voltammetry of these open layer species shows the existence of two reversible processes, related to reduction and oxidation, to stable charged species. The chemical oxidation of both radical adducts gives rise to stable cations, whose fundamental state has a biradical triplet electronic structure or a closed shell singlet character, depending on the electronic conjugation between the donor and acceptor electron moieties. The presence of chlorines adjacent to the nitrogen in 1 breaks the conjugation between both halves, facilitating the formation of a triplet electronic state of the cation, while the absence of chlorines in these positions in 2 facilitates partial conjugation and stabilizes the closed shell singlet electronic state of the cation.

Synthesis of Linear and V-Shaped Carbazolyl-Substituted Pyridine-3,5-dicarbonitriles Exhibiting Efficient Bipolar Charge Transport and E-Type Fluorescence

With the aim of developing all-organic bipolar semiconductors with high charge mobility and efficient E-type fluorescence (so-called TADF) as environmentally friendly light-emitting materials for optoelectronic applications, four noble metals-free dyes with linear and V-shapes were designed using accepting pyridine-3,5-dicarbonitrile and donating carbazole units. By exploiting a donor-acceptor design strategy and using moieties with different donating and accepting abilities, TADF emitters with a wide variety of molecular weights were synthesized to achieve the optimum combination of charge-transporting and fluorescent properties in one TADF molecule. Depending on molecule structures, different TADF emitters capable of emitting in the range from 453 to 550 nm with photoluminescence quantum yields up to 98 % for the solutions in oxygen-free toluene were obtained. All compounds showed bipolar charge-transport. Hole mobility of 2.8×10^-3  cm² /Vs at 7×10⁵  V cm^-1 was observed for the compound containing two di-tert-butyl-substituted carbazole moieties. The compounds were tested in both non-doped and doped organic light-emitting diodes using different hosts. It was shown that the developed TADF emitters are suitable for different color devices with electroluminescence ranging from blue to yellow and with brightness, maximum current and external quantum efficiencies exceeding 10 000 cd m^-2 , 15 cd/A, and 7 %, respectively.

Towards direct enzyme wiring: a theoretical investigation of charge carrier transfer mechanisms between glucose oxidase and organic semiconductors

In this work, a general theoretical and numerical approach based on semiconductor theory, which could be applied to a study of direct enzyme wiring, has been discussed. Marcus-Hush theory was applied to evaluate the potential transfer of charge carriers (holes and electrons) between glucose oxidase (GOx) and organic semiconductors. Two mechanisms of multistep hopping of charge to/from the oxidised/reduced flavin-based moiety through residues of aromatic amino acids located in GOx and long range charge direct tunnelling from the cofactor to the organic semiconductor surface have been proposed and evaluated. It was determined that the hole-hopping mechanism is possible and proceeds at a low ionization potential of the organic semiconductor. The calculations reveal that hopping of electrons is blocked, but direct electron tunnelling between the cofactor and the organic semiconductor is still probable. The most optimal conditions and tunable characteristics of GOx-based biosensors such as the ionization potential, electron affinity of organic semiconductors and distance between the enzyme and surface were estimated for the first time.

Experimental and Theoretical Investigations of an Electrochromic Azobenzene and 3,4-Ethylenedioxythiophene-based Electrochemically Formed Polymeric Semiconductor

An electrochromic material based on azobenzene and 3,4-ethylenedioxythiophene (EDOT) semiconducting layer was electrochemically deposited on an indium tin oxide coated glass electrode. Chemical synthesis of the azobenzene and EDOT-based chromophore (DAE) and electrochemical formation of its corresponding polymer (pDAE) are reported. The electrochromic properties of the synthesized polymer pDAE were investigated by electrochemical and spectroelectrochemical methods. pDAE exhibited an optical bandgap of 1.82 eV and three distinct colored states in its reduced, neutral, and oxidized forms. The pDAE polymer showed 44 % optical contrast at 710 nm between its reduced and oxidized states and a fast electrochromic switching time of 1.0 s. The frontier molecular orbitals, Raman shifts, and semiconducting properties of this electrochromic polymer were evaluated by density functional theory calculations. The optical absorption bands of the polymer charged states were assigned and investigated.

3,3'-Bicarbazole-Based Host Molecules for Solution-Processed Phosphorescent OLEDs

Solution-processed organic light-emitting diodes (OLEDs) are attractive due to their low-cost, large area displays, and lighting features. Small molecules as well as polymers can be used as host materials within the solution-processed emitting layer. Herein, we report two 3,3′-bicarbazole-based host small molecules, which possess a structural isomer relationship. 9,9′-Di-4-n-butylphenyl-9H,9′H-3,3′-bicarbazole (BCz-nBuPh) and 9,9′-di-4-t-butylphenyl-9H,9′H-3,3′-bicarbazole (BCz-tBuPh) exhibited similar optical properties within solutions but different photoluminescence within films. A solution-processed green phosphorescent OLED with the BCz-tBuPh host exhibited a high maximum current efficiency and power efficiency of 43.1 cd/A and 40.0 lm/W, respectively, compared to the device with the BCz-nBuPh host.

Pyrenyl substituted 1,8-naphthalimide as a new material for weak efficiency-roll-off red OLEDs: a theoretical and experimental study

On the basis of the theoretical calculations of semiconducting properties, a new derivative ImPy for red OLEDs has been developed.

Solid-state organization of n-type carbazole-based semiconductors for organic thin-film transistors

n-Type OTFTs were fabricated and characterised from a series of tricyanovinyl-substituted carbazole-based materials with different N-alkyl chain lengths as active layers. XRD studies gave insights into the main intermolecular interactions, molecular packing motifs and the degree of molecular order in thin films that justified the performance of the devices.

Interface engineering and solid-state organization for triindole-based p-type organic thin-film transistors

Role of the solid-state organization of the semiconductor and of its interface with the dielectric on the OTFT performance.