Electrochemical and spectroelectrochemical studies on the reactivity of perimidine–carbazole–thiophene monomers towards the formation of multidimensional macromolecules versus stable π-dimeric states

During research on cross-linked conducting polymers, double-functionalized monomers were synthesized. Two subunits potentially able to undergo oxidative coupling were used—perimidine and, respectively, carbazole, 3,6-di(hexylthiophene)carbazole or 3,6-di(decyloxythiophene)carbazole; alkyl and alkoxy chains as groups supporting molecular ordering and 14H-benzo[4,5]isoquinone[2,1-a]perimidin-14-one segment promoting CH· · · O interactions and π–π stacking. Electrochemical, spectroelectrochemical, and density functional theory (DFT) studies have shown that potential-controlled oxidation enables polarization of a specific monomer subunit, thus allowing for simultane-ous coupling via perimidine and/or carbazole, but mainly leading to dimer formation. The reason for this was the considerable stability of the dicationic and tetracationic π-dimers over covalent bonding. In the case of perimidine-3,6-di(hexylthiophene)carbazole, the polymer was not obtained due to the steric hindrance of the alkyl substituents preventing the coupling of the monomer radical cations. The only linear π-conjugated polymer was obtained through di(decyloxythiophene)carbazole segment from perimidine-di(decyloxythiophene)-carbazole precursor. Due to the significant difference in potentials between subsequent oxidation states of monomer, it was impossible to polarize the entire molecule, so that both directions of coupling could be equally favored. Subsequent oxidation of this polymer to polarize the side perimidine groups did not allow further crosslinking, because rather the π–π interactions between these perimidine segments dominate in the solid product

Electrochemical tailoring of the TADF emitters, how to decrease the ΔEST gap by increasing the conjugation of the donor

This work presents an investigation of three xanthone derivatives as the emitters for organic light-emitting diode applications. Through extensive photophysical and electrochemical studies, the thermally activated delayed fluorescence effect was observed and further applied in devices. Due to the substantial ΔEST gap, the final efficiency of the OLED was below 5%. The drop in the charge transfer energy was observed with electrochemical dimerisation of the donor molecule and increased molecule conjugation. The synthesised polymers exhibited an efficient thermally activated delayed fluorescence process through the shift of the singlet excited state energy level and decreased the ΔEST from 0.42 eV for the XNAP monomer material down to 0.12 eV for the polymerised derivative and final increase of the OLED device efficiency. Thus, the study presents the possibility of synthesising and tailoring many thermally activated delayed fluorescence emitters through electropolymerisation and applying this technique in working light-emitting devices

Exohedral functionalization of fullerene by substituents controlling of molecular organization for spontaneous c60 dimerization in liquid crystal solutions and in a bulk controlled by a potential

A study was carried out on the possibility of orderly and spontaneous dimerization at room temperature of C60 cages in fullerene liquid crystal fullerene dyads (R-C60). For this purpose, dyads with a structural elements feature supporting π-stacking and Van der Waals interactions were tested, due to the presence of terthiophene donors linked through an α-position or dodecyloxy chains. In addition, this possibility was also tested and compared to dyads with shorter substituents and the pristine C60. Research has shown that only in dyads with the features of liquid crystals, π-dimerization of C60 units occurs, which was verified by electrochemical and spectroelectrochemical (ESR) measurements. Cyclic voltammetry and differential voltammetry studies reveal π-dimeriza-tion in liquid crystal dyad solution even without the possibility of previous polymerization (ca-thodic or anodic) under conditions in the absence of irradiation and without the availability of reaction initiators, and even with the use of preliminary homogenization. These dyads undergo six sequential, one-electron reductions of π-dimer (R-C60···C60-R), where two electrons are added suc-cessively to each of the two fullerene cages and first form two radical anion system (R-C60)•−(R-C60)•− without pairing with the characteristics of two doublets. Similarly, the second reductions of π-dimer occur at potentials that are close to the reduction potential for the conversion to a system of two triplet dianions (R-C60)2−(R-C60)2−. Electron paramagnetic resonance spectra indicate a significant interaction between C60 cages. Interestingly, the strength of intermolecular bonds is so significant that it can overcome Coulombic repulsion, even with such highly charged particles as dianions and tri-anions. Such behavior has been revealed and studied so far only in covalently bonded C60 dimers

Acridone-amine D-A-D thermally activated delayed fluorescence emitters with narrow resolved electroluminescence and their electrochromic properties

Acridones have found their role in luminescent materials for OLEDs. Most interestingly, showing potential as weak charge transfer thermally activated delayed fluorescence (TADF) emitters, providing narrow photoluminescence. In this work, we present a comprehensive study of donor-acceptor-donor (D-A-D) acridone-amine derivatives showing TADF and UV electrochromic properties. Structure-property relationships are studied using electrochemical and spectroelectrochemical methods as well as using photophysical characterization. Most successful emitters are used as luminescent materials in OLED, showing narrow (FWHM = 66-85 nm) electroluminescence in the green region with maximum EQE = 5.4%