Copolymers Containing 1-Methyl-2-phenyl-imidazole Moieties as Permanent Dipole Generating Units: Synthesis, Spectroscopic, Electrochemical, and Photovoltaic Properties.

New donor-acceptor conjugated alternating or random copolymers containing 1-methyl-2-phenylbenzimidazole and benzothiadiazole (P1), diketopyrrolopyrrole (P4), or both acceptors (P2) are reported. The specific feature of these copolymers is the presence of a permanent dipole-bearing moiety (1-methyl-2-phenyl imidazole (MPI)) fused with the 1,4-phenylene ring of the polymer main chain. For comparative reasons, polymers of the same main chain but deprived of the MPI group were prepared, namely, P5 with diketopyrrolopyrrole and P3 with both acceptors. The presence of the permanent dipole results in an increase of the optical band gap from 1.51 eV in P3 to 1.57 eV in P2 and from 1.49 eV in P5 to 1.55 eV in P4. It also has a measurable effect on the ionization potential (IP) and electrochemical band gap (EgCV), leading to their decrease from 5.00 and 1.83 eV in P3 to 4.92 and 1.79 eV in P2 as well as from 5.09 and 1.87 eV in P5 to 4.94 and 1.81 eV in P4. Moreover, the presence of permanent dipole lowers the exciton binding energy (Eb) from 0.32 eV in P3 to 0.22 eV in P2 and from 0.38 eV in P5 to 0.26 eV in P4. These dipole-induced changes in the polymer properties should be beneficial for photovoltaic applications. Bulk heterojunction solar cells fabricated from these polymers (with PC71BM acceptor) show low series resistance (rs), indicating good electrical transport properties. The measured power conversion efficiency (PCE) of 0.54% is limited by the unfavorable morphology of the active layer.

Effect of the substituent position on the electrochemical, optical and structural properties of donor-acceptor type acridone derivatives.

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[combining macron] 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.

Direct Reductive Cyclocondensation of the Nitro Group with the Amido Group: Key Role of the Iminophosphorane Intermediate in the Synthesis of 1,4-Dibenzodiazepine Derivatives.

A class of dialkylamino-substituted dibenzodiazepines and their hetero analogues was synthesized by the intramolecular aza-Wittig condensation of the amido group with iminophosphoranes. The one-pot, two-step procedure includes reductive synthesis of the intermediate iminophosphoranes from the corresponding nitroamides and tributylphosphine.

Highly Efficient Tuning of Ferromagnetic Spin Interactions in High-Spin Arylamine Structures by Incorporation of Spin Bearing Carbazole Units.

Arylamine moieties oxidized to radical cations are considered promising spin bearing units in high-spin-type compounds. Here, we report the first use of carbazole-3,6-diamine units as efficient, rigid spin containing units. The use of rigid spin bearing units enhances significantly spin exchange interactions. The design using density functional theory calculations shows the progressive increase of the exchange coupling constant dependent on the considered model molecules. Two of the most representative molecules containing flexible (dimer 1) and rigid spin coupling unit (dimer 2) were synthesized. Electrochemical and pulsed-electron paramagnetic resonance nutation studies showed that both dimers can be oxidized to yield a majority of dicationic diradicals exhibiting S = 1 ground states. The high values of the dimer 2 exchange coupling constant obtained both computationally ( J/ kB = 145 K; HHeis. = - JS1 S2) and experimentally ( J/ kB = 90-100 K) indicate the beneficial role of the carbazole moiety incorporated into spin bearing units.

High-Spin Polymers: Ferromagnetic Coupling of S = 1 Hexaazacyclophane Units up to a Pure S = 2 Polycyclophane.

Triarylamines oxidized to radical cations can be used as stable spins sources for the design of high-spin compounds. Here, we present the synthesis of the polyarylamine-containing hexaazacyclophanes linked via meta-terphenyl bridges. Spins, created after oxidation of the polymer, can be coupled magnetically in cyclophane moieties via meta-phenyl and along the polymer chain via meta-terphenyl units. The formation of a quintet spin state was evidenced by pulsed-EPR nutation spectroscopy. Two exchange coupling constants via both couplers were determined experimentally and corresponded to J/k = 89 K in the cyclophane moiety and j/k = 17 K via meta-terphenyl. Most importantly, in this polymer, four spins can be ferromagnetically ordered via both couplers, which leads to the high spin state.

Formation of High-Spin States (S = 3/2 and 2) in Linear Oligo- and Polyarylamines.

This article describes the study of a linear trimer and three polyarylamines PB1-3 containing a 3,4'-biphenyl ferromagnetic coupler. The synthesis of the model compound (trimer) and the polymers has been presented. The formation of radical cations was studied using electrochemical and optical (UV-vis) methods. The chemical oxidation of these compounds leads to the creation of high-spin states, evidenced by pulsed EPR nutation spectroscopy. A quartet spin state is observed for the trimer model compound, and its J exchange coupling constant has been measured experimentally (J/k = 11.8 K) and compared quantitatively to DFT calculations. Most importantly, quartet and quintet spin states have been formed for PB3 and PB2, respectively. These last two doped polymers thus exhibit the highest spin states observed to date for linear polyarylamine compounds.

Raman changes induced by electrochemical oxidation of poly(triarylamine)s: toward a relationship between molecular structure modifications and charge generation.

Linear, alternating polymers of aromatic amines (p-phenylenediamine, bis(p-aminophenyl)amine, and diaminocarbazole) and either m-phenylene or 3,5-pyridine have been synthesized and characterized by electrochemical and spectroscopic means. The presence of radical cations in their electrochemically oxidized forms is manifested by new bands in the UV-vis-NIR spectra whose appearance can be correlated with reversible redox couples registered in the corresponding cyclic voltammograms at approximately the same potentials as well as with pronounced evolutions of their resonance Raman spectra. Detailed analysis of the Raman data gives information about the locations and the distribution of radical cations and spinless dication in the macromolecule. This approach can provide a new insight into the formation of high-spin states in these polymers.

Ferromagnetic Spin Coupling through the 3,4'-Biphenyl Moiety in Arylamine Oligomers-Experimental and Computational Study.

This report describes the study of a dimer d2+ and a linear trimer t3+ of amminium radical cations coupled by 3,4'-biphenyl spin coupling units. The synthesis of the parent diamine and triamine and their optical and electrochemical properties obtained by UV-visible and cyclic voltammetry are presented. The chemical doping of the parent diamine d and triamine t was performed quantitatively to obtain samples containing the corresponding dimer d2+ and trimer t3+ in almost pure high-spin states as evidenced by pulsed EPR nutation spectroscopy. The J coupling constants of the corresponding S = 1 and S = 3/2 spin states were measured (J/k = 135 K) and compared quantitatively to DFT calculations.

Vibrational dynamics in dendridic oligoarylamines by Raman spectroscopy and incoherent inelastic neutron scattering.

Vibrational dynamics in triarylamine dendrimers was studied in a complementary way by Raman and infrared (IR) spectroscopies and incoherent inelastic neutron scattering (IINS). Three molecules were investigated, namely, unsubstituted triarylamine dendrimer of the first generation and two dendrimers of the first and second generation, substituted in the crown with butyl groups. To facilitate the assignment of the observed IR and Raman modes as well as the IINS peaks, vibrational models, based on the general valence force field method (GVFF), were calculated for all three compounds studied. A perfect consistency between the calculated and experimental results was found. Moreover, an important complementarity of the vibrational spectroscopies and IINS was established for the investigated dendrimers. The IINS peaks originating mainly from the C-H motions were not restricted by particular selection rules and only dependent on the IINS cross section. To the contrary, Raman and IR bands were imposed by the selection rules and the local geometry of the dendrimers yielding mainly C-C and C-N deformation modes with those of C-H nature of much lower intensity. Raman spectroscopy was also applied to the studies of the oxidation of dendrimers to their cationic forms. A strong Raman resonance effect was observed, since the spectra of the studied compounds, registered at different levels of their oxidation, strongly depended on the position of the excitation line with respect to their electronic spectrum. In particular, the blue (458 nm) excitation line turned out to be insensitive toward the cationic forms yielding very limited spectral information. To the contrary, the use of the red (647 nm) and infrared (1064 nm) excitation lines allowed for an unambiguous monitoring of the spectral changes in dendrimers oxidized to nominally monocationic and tricationic states. The analysis of oxidation-induced spectral changes in the tricationic state indicated that the charge storage configuration predominantly involved one spinless dication of the quinoid bond sequence and one radical cation. However, small numbers of dications were also found in a nominally monocationic state, where only radical cations should have been present. This finding was indicative of some inhomogeneity of the oxidation.

Polymers for electronics and spintronics.

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.

Tuning of ferromagnetic spin interactions in polymeric aromatic amines via modification of their π-conjugated system.

Polyarylamine containing meta-para-para-aniline units in the main chain and meta-para-aniline units in the pendant chains was synthesized. The polymer can be oxidized to radical cations in chemical or electrochemical ways. The presence of meta-phenylenes in the polymer chemical structure allows for the ferromagnetic coupling of electronic spins, which leads to the formation of high spin states. Detailed pulsed-EPR study indicates that the S = 2 spin state was reached for the best oxidation level. Quantitative magnetization measurements reveal that the doped polymer contains mainly S = 2 spin states and a fraction of S = 3/2 spin states. The efficiency of the oxidation was determined to be 74%. To the best of our knowledge, this polymer is the first example of a linear doped polyarylamine combining such high spin states with high doping efficiency.

Magnetic properties of a doped linear polyarylamine bearing a high concentration of coupled spins (S = 1).

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).

Ferromagnetic spins interaction in tetraaza- and hexaazacyclophanes.

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.

High-spin radical cations of alternating poly(m-p-anilines).

Three alternating poly(m-p-anilines) have been synthesized via palladium-catalyzed amination reactions. Polymers were oxidized to radical cations by the use of chemical and electrochemical methods. The presence of radical cations was manifested by the appearance of two new bands in UV-vis spectra and a strong EPR signal. Moreover, EPR spectra at low temperatures confirmed the formation of a high-spin state. The magnetization measurements of polymers oxidized to radical cations revealed the paramagnetic-type behavior with weak antiferromagnetic interactions. Radical cations underwent the degradation processes in the presence of air, which led to the decrease of spin concentration.

Molecular weight dependent charge carrier mobility in poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene).

Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight.