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Four donor-acceptor-donor compounds consisting of 9,9-dimethyl-9,10-dihydroacridine donors differently linked to a benzothiadiazole acceptor were designed using DFT calculations and synthesized, namely 4,7-bis(4-(9,9-dimethyl-9,10-dihydroacridine)phenyl)benzo[c][1,2,5]thiadiazole (1), 4,7-bis(2,5-dimethyl-4-(9,9-dimethyl-9,10-dihydroacridine)phenyl)benzo[c][1,2,5]thiadiazole (2), 4,7-bis(3,5-di(9,9-dimethyl-9,10-dihydroacridine)phenyl)benzo[c][1,2,5]thiadiazole (3), and 4-(3,5-di(9,9-dimethyl-9,10-dihydroacridine)phenyl)-7-(thiophen-2-yl)benzo[c][1,2,5]thiadiazole (4). As predicted theoretically, all studied compounds were electrochemically active both in the reduction as well as in the oxidation modes. They underwent one electron quasi-reversible reduction. Oxidation of 1 and 2 involved a two electron process transforming them into dications and carrying out, in parallel, their dimerization. Oxidation of 3 and 4 resulted in their oligomerization (polymerization). The electrochemically determined ionisation potentials (IP) of 1-4 were similar, covering a narrow range of 5.28-5.33 eV and were consistent with DFT calculations. Larger differences were found for experimentally determined electron affinity (EA) values, being significantly lower for 2 (|EA| = 2.59 eV) as compared to 1, 3 and 4 whose |EA| values were higher by 0.15-0.25 eV, again consistent with DFT calculations. DFT calculations predict positive values of ΔE(S1-T1) for all compounds i.e. in the range of 0.18 eV to 0.43 eV for 1, 3 and 4 and a significantly lower value for 2 (0.06 eV), indicating a possible RISC process in this case. DFT calculations of ΔE(S1-T2) lead to negative and very small values for 2-4 implying a possible involvement of higher lying triplets in the generation of singlet excitons. The investigated derivatives exhibited fluorescence in the orange-red spectral range (550-770 nm) and were strongly dependent on the solvent polarity. The highest PLQY value of 37% was measured for 1 in toluene. The PLQY values significantly improved upon deoxygenation of the studied solutions. Solid state samples also exhibited higher PLQY values as compared to those determined for DCM solutions. These findings were rationalized by partial suppression of the vibrationally induced emission quenching in the solid state due to the intermolecular interaction confinement. [ABSTRACT FROM AUTHOR]

Six acridone (quinacridone) derivatives containing either carbazole or phenoxazine substituents were designed and synthesized with the aim of elucidating the effect of the donor (D) and acceptor (A) linking pattern (D–A, D–A–D or D–π–A–π–D) on their photophysical and electrochemical properties. These new electroactive compounds combine reversible electrochemical oxidation with excellent luminescent properties. Their electrochemically determined ionization potentials (IPs) are in the range from 5.09 eV to 5.45 eV, higher for derivatives with carbazole donors as compared to phenoxazine ones. The measured electron affinities (EAs) are in the range from −2.53 eV to −2.64 eV with the exception of the quinacridone derivative showing EA of −3.03 eV. Their vacuum-deposited films emit radiation in a wide spectral range from sky-blue to red. Compounds with carbazole moieties (compounds 1, 2 and 6 in the subsequent text) showed prompt fluorescence and aggregation-caused quenching. Photoluminescent quantum yields (PLQYs) of their toluene solutions reached values up to 69%. Compounds containing phenoxazine moieties (compounds marked as 3–5) demonstrated thermally activated delayed fluorescence (TADF) and aggregation-induced emission enhancement (AIEE). Their neat films showed PLQYs of 35%. Quinacridone disubstituted with carbazole (compound 6) showed the highest hole mobility reaching 2.53 × 10−3 cm2 V−1 s−1 at electric field of 3.6 × 105 V cm−1. Carbazolyl disubstituted acridone (compound 2) and phenoxazinyl monosubstituted acridone (compound 3) turned out to be ambipolar compounds showing reasonably balanced electron and hole mobilities. The appropriate combination of redox, transport and luminescent properties makes the studied compounds suitable candidates for optoelectronic applications. Test OLEDs fabricated from 3 exhibited maximum external quantum efficiencies reaching 16.7%. Finally, an excellent agreement between the experimental results and those obtained by DFT calculations should be stressed. The basics for selection according to the user needs of either D–A, D–A–D or D–π–A–π–D types of molecular structures of TADF/AIEE luminophores are provided in this study. [ABSTRACT FROM AUTHOR]

Three new donor–acceptor (D–A) compounds, positional isomers of phenoxazine-substituted acridone, namely 1-phenoxazine-N-hexylacridone (o-A), 2-phenoxazine-N-hexylacridone (m-A) and 3-phenoxazine-N-hexylacridone (p-A), were synthesized. The synthesized compounds showed interesting, isomerism-dependent electrochemistry. Their oxidation was reversible and their potential (given vs. Fc/Fc+) changed from 0.21 V for o-A to 0.36 V for p-A. In contrast, their reduction was irreversible, isomerism-independent and occurred at rather low potentials (ca. −2.25 to −2.28 V). The electrochemical results led to the following values of the ionization potentials (IPs) and electron affinities (EAs): 5.03 eV and −2.14 eV, 5.15 eV and −2.20 eV, and 5.20 eV and −2.28 eV for o-A , m-A and p-A , respectively. The experimentally obtained values were in very good agreement with those predicted by DFT calculations. All three isomers readily formed single crystals suitable for their structure determination. o-A and p-A crystallized in P1¯ and P21/n space groups, respectively, with one molecule per asymmetric unit, while m-A crystallized in the P21/c space group with two molecules in the asymmetric unit accompanied by disordered solvent molecules. The UV-vis spectra of the studied compounds were isomerism and solvent independent, yielding absorption maxima in the vicinity of 400 nm. Their photoluminescence spectra, in turn, strongly depended on isomerism and the used solvent showing smaller Stokes shifts for the emission bands registered in toluene as compared to the corresponding bands measured in dichloromethane. The photoluminescence quantum yields (φ) were systematically higher for toluene solutions reaching the highest value of 20% for p-A. For all three isomers studied, stationary and time-resolved spectroscopic investigations carried out in toluene at different temperatures revealed spectral features indicating a contribution of thermally activated delayed fluorescence (TADF) to the observed spectroscopic behaviour. The measured photoluminescence quantum yields (φ) were higher for solid state films of pure compounds and for their dispersions in solid matrices (zeonex) than those recorded for toluene and dichloromethane solutions of the studied phenoxazine-N-hexylacridone isomers. The obtained experimental spectroscopic and structural data were confronted with theoretical predictions based on DFT calculations. [ABSTRACT FROM AUTHOR]

Arylamine moieties oxidized to radical cations are promising spin bearers for organic high-spin compounds. However, successive oxidations of next-neighbour sites as well as the resulting ferromagnetic exchange interactions depend strongly on the charge and spin distributions over the molecule. We report here that the use of rigid segments composed of m-phenylene spin couplers linked to arylamine spin bearers in a co-planar way facilitates successive oxidations, enhances spin exchange interactions and doubles the observed spin state (S = 2) in a polymer (PQA) when compared to the chemically equivalent (but locally free rotating) PA2 polymer (S = 1). Such a quintet spin state is observed for the first time for a linear polyarylamine with an m-phenylene coupler. DFT calculations of the dimer QA reproduce the experimental J value and indicate that oxidation of these co-planar compounds leads indeed to well localized radical cations, a fact of crucial importance for the preparation of arylamine-type high-spin materials. [ABSTRACT FROM AUTHOR]

This critical review is devoted to semiconducting and high spin polymers which are of great scientific interest in view of further development of the organic electronics and the emerging organic spintronic fields. Diversified synthetic strategies are discussed in detail leading to high molecular mass compounds showing appropriate redox (ionization potential (IP), electron affinity (EA)), electronic (charge carrier mobility, conductivity), optoelectronic (electroluminescence, photoconductivity) and magnetic (magnetization, ferromagnetic spin interactions) properties and used as active components of devices such as n- and p-channel field effect transistors, ambipolar light emitting transistors, light emitting diodes, photovoltaic cells, photodiodes, magnetic photoswitches, etc. Solution processing procedures developed with the goal of depositing highly ordered and oriented films of these polymers are also described. This is completed by the description of principal methods that are used for characterizing these macromolecular compounds both in solution and in the solid state. These involve various spectroscopic methods (UV-vis-NIR, UPS, pulse EPR), electrochemistry and spectroelectrochemistry, magnetic measurements (SQUID), and structural and morphological investigations (X-ray diffraction, STM, AFM). Finally, four classes of polymers are discussed in detail with special emphasis on the results obtained in the past three years: (i) high IP, (ii) high ☋EA☋, (iii) low band gap and (iv) high spin ones. [ABSTRACT FROM AUTHOR]

Magnetic properties of a doped linear polyarylamine (PA2), whose chain includes alternating para-phenylene and meta-phenylene groups, and of two cyclic and linear model compounds (C2 and D2) were explored by pulsed-EPR nutation spectroscopy, SQUID magnetometry and DFT calculations. Stoichiometrically doped PA2 samples exhibit a pure S = 1 state (exchange coupling constant J = 18 K) with a high spin concentration (0.65) corresponding to 65% of mers bearing holes. Such properties were already observed for doped reticulated polyarylamines but are quite unusual for doped linear polyarylamines. In order to better understand the properties of PA2, model compounds C2 and D2 were also investigated: pure S = 1 spin states could also be obtained, but with higher J (respectively 57 K and 35 K) and, surprisingly, with high but still limited spin concentrations (respectively 0.77 and 0.65).

Teraaza- and hexaazacyclophanes have been synthesized via a one-step palladium catalyzed amination reaction. The chemical oxidation of cyclophanes leads to the formation of radical cations, the presence of which was manifested by the appearance of new bands in UV-Vis-NIR and IR spectra. Spins of radical cations can be magnetically coupled. The nutation pulsed-EPR technique (PEANUT experiment) enables us to determine the multiplicity of the systems for different oxidant/cyclophane ratios. Spins of cyclophanes oxidized to diradical dications interact ferromagnetically to form a pure triplet state.