D-A-D Compounds Combining Dithienopyrrole Donors and Acceptors of Increasing Electron-Withdrawing Capability: Synthesis, Spectroscopy, Electropolymerization, and Electrochromism.

Five D-π-A-π-D compounds consisting of the same donor unit (dithieno[3,2-b:2',3'-d]pyrrole, DTP), the same π-linker (2,5-thienylene), and different acceptors of increasing electron-withdrawing ability (1,3,4-thiadiazole (TD), benzo[c][1,2,5]thiadiazole (BTD), 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP), 1,2,4,5-tetrazine (TZ), and benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone (NDI)) were synthesized. DTP-TD, DTP-BTD, and DTP-DPP turned out to be interesting luminophores emitting either yellow (DTP-TD) or near-infrared (DTP-BTD and DTP-DPP) radiation in dichloromethane solutions. The emission bands were increasingly bathochromically shifted with increasing solvent polarity. Electrochemically determined electron affinities (|EA|s) were found to be strongly dependent on the nature of the acceptor changing from 2.86 to 3.84 eV for DTP-TD and DTP-NDI, respectively, while the ionization potential (IP) values varied only weakly. Experimental findings were strongly supported by theoretical calculations, which correctly predicted the observed solvent dependence of the emission spectra. Similarly, the calculated IP and EA values were in excellent agreement with the experiment. DTP-TD, DTP-BTD, DTP-TZ, and DTP-NDI could be electropolymerized to yield polymers of very narrow electrochemical band gap and characterized by redox states differing in color coordinates and lightness. Poly(DTP-NDI) and poly(DTP-TD) showed promising electrochromic behavior, not only providing a rich color palette in the visible but also exhibiting near-infrared (NIR) electrochromism.

9,10-Anthraquinones Disubstituted with Linear Alkoxy Groups: Spectroscopy, Electrochemistry, and Peculiarities of Their 2D and 3D Supramolecular Organizations.

Spectroscopic, electrochemical, and structural properties of 2,6-dialkoxy-9,10-anthraquinones (Anth-OCn, n = 4, 6, 8, 10, and 12) of increasing alkoxy substituents length were investigated. UV-vis spectroscopy showed a substitution-induced bathochromic shift of the least energetic band from 325 nm in the case of unsubstituted anthraquinone to ca. 350 nm for the studied derivatives. Similarly as unsubstituted anthraquinone, the studied compound showed two reversible one electron reductions to a radical anion and spinless anions, respectively. The first reduction was affected by electron-donating properties of the substituents, its potential being shifted to ca. -1.5 V (vs Fc/Fc+), i.e., by 80 to 95 mV as compared to the case of unsubstituted anthraquinone. This corresponded to a decrease of |EA| from 3.27 to 3.19-3.17 eV. The experimental spectroscopic and electrochemical data were in full agreement with the DFT calculations. The introduction of the alkoxy substituent improved solution processibility of the studied compounds and facilitated the formation of their ordered supramolecular 2D aggregation on HOPG as well as single crystal growth from solutions. Comparative structural investigations carried out on single crystals and monolayers deposited on HOPG revealed two, mutually related, effects of the substituent length on the resulting supramolecular organization. The first one concerns both the 2D organization in the monolayers and 3D molecular arrangement in crystals: increasing substituent length evolution of the structure occurs from herringbone-type to lamellar. The second effect, observed in monolayers of the derivatives with longer substituents, concerns gradual evolution of their lamellar structures with increasing substituent length. This evolution is induced by the structure of the graphite substrate and involves increasing correlation of the molecules orientation (anthraquinone cores as well as alkoxy substituents) with the symmetry of the graphite substrate. As a result, their 2D and 3D structures become dissimilar.

Self-Assembly Properties of Solution Processable, Electroactive Alkoxy, and Alkylthienylene Derivatives of Fused Benzoacridines: A Scanning Tunneling Microscopy Study.

Self-organization in mono- and bilayers on HOPG of two groups of benz[5,6]acridino[2,1,9,8-klmna]acridine derivatives, namely, 8,16-dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines with an increasing alkoxy substituent length and 8,16-bis(3- or 4- or 5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines, i.e., three positional isomers of the same benzoacridine, is investigated by scanning tunneling microscopy. The layers were deposited from a solution of the adsorbate (in hexane or dichloromethane) and imaged ex situ at molecular resolution. In all cases, the resulting two-dimensional (2D) supramolecular organization is governed by the interactions between large, fused heteroaromatic cores that form densely packed rows separated by areas covered by substituents. In 8,16-dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines, the alkoxy substituents, separating the rows of densely packed cores, are interdigitated. An increasing substituent length leads to an intuitively expected increase in this 2D unit cell parameter that corresponds to the orientation of the substituent in the monolayer. In the case of 8,16-bis(3- or 4- or 5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine positional isomers, the self-assembly processes are more complex. Although the determined 2D unit cell is in all cases essentially the same, the role of alkylthienylene substituents in layer formation is distinctly different. Thus, the formation of monolayers and bilayers is very sensitive to isomerism. 8,16-Bis(5-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine is capable of forming the most stable monolayer and the most labile bilayer. In the case of 8,16-bis(3-octylthiophen-2-yl)benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine, an inverse phenomenon is observed leading to the most labile monolayer and the most stable bilayer. These differences are rationalized in terms of dissimilar molecular geometries of the studied isomers and different interdigitation patterns in their 2D supramolecular structures.

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.

Low and High Molecular Mass Dithienopyrrole-Naphthalene Bisimide Donor-Acceptor Compounds: Synthesis, Electrochemical and Spectroelectrochemical Behaviour.

Two low molecular weight electroactive donor-acceptor-donor (DAD)-type molecules are reported, namely naphthalene bisimide (NBI) symmetrically core-functionalized with dithienopyrrole (NBI-(DTP)2 ) and an asymmetric core-functionalized naphthalene bisimide with dithienopyrrole (DTP) substituent on one side and 2-ethylhexylamine on the other side (NBI-DTP-NHEtHex). Both compounds are characterized by low optical bandgaps (1.52 and 1.65 eV, respectively). NBI-(DTP)2 undergoes oxidative electropolymerization giving the electroactive polymer of ambipolar character. Its two-step reversible reduction and oxidation is corroborated by complementary EPR and UV/Vis-NIR spectroelectrochemical investigations. The polymer turned out to be electrochemically active not only in aprotic solvents but also in aqueous electrolytes, showing a distinct photocathodic current attributed to proton reduction. Additionally, poly(NBI-(DTP)2 ) was successfully tested as a photodiode material.

Star-Shaped Conjugated Molecules with Oxa- or Thiadiazole Bithiophene Side Arms.

Star-shaped conjugated molecules, consisting of a benzene central unit symmetrically trisubstituted with either oxa- or thiadiazole bithiophene groups, were synthesized as promising molecules and building blocks for application in (opto)electronics and electrochromic devices. Their optical (Eg (opt)) as well as electrochemical (Eg (electro)) band gaps depended on the type of the side arm and the number of solubilizing alkyl substituents. Oxadiazole derivatives showed Eg (opt) slightly below 3 eV and by 0.2 eV larger than those determined for thiadiazole-based compounds. The presence of alkyl substituents in the arms additionally lowered the band gap. The obtained compounds were efficient electroluminophores in guest/host-type light-emitting diodes. They also showed a strong tendency to self-organize in monolayers deposited on graphite, as evidenced by scanning tunneling microscopy. The structural studies by X-ray scattering revealed the formation of supramolecular columnar stacks in which the molecules were organized. Differences in macroscopic alignment in the specimen indicated variations in the self-assembly mechanism between the molecules. The compounds as trifunctional monomers were electrochemically polymerized to yield the corresponding polymer network. As shown by UV/Vis-NIR spectroelectrochemical studies, these networks exhibited reversible electrochromic behavior both in the oxidation and in the reduction modes.

Soluble Flavanthrone Derivatives: Synthesis, Characterization, and Application to Organic Light-Emitting Diodes.

Simple modification of benzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine-8,16-dione, an old and almost-forgotten vat dye, by reduction of its carbonyl groups and subsequent O-alkylation, yields solution-processable, electroactive, conjugated compounds of the periazaacene type, suitable for the use in organic electronics. Their electrochemically determined ionization potential and electron affinity of about 5.2 and -3.2 eV, respectively, are essentially independent of the length of the alkoxyl substituent and in good agreement with DFT calculations. The crystal structure of 8,16-dioctyloxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridine (FC-8), the most promising compound, was solved. It crystallizes in space group P1‾ and forms π-stacked columns held together in the 3D structure by dispersion forces, mainly between interdigitated alkyl chains. Molecules of FC-8 have a strong tendency to self-organize in monolayers deposited on a highly oriented pyrolytic graphite surface, as observed by STM. 8,16-Dialkoxybenzo[h]benz[5,6]acridino[2,1,9,8-klmna]acridines are highly luminescent, and all have photoluminescence quantum yields of about 80 %. They show efficient electroluminescence, and can be used as guest molecules with a 4,4'-bis(N-carbazolyl)-1,1'-biphenyl host in guest/host-type organic light-emitting diodes. The best fabricated diodes showed a luminance of about 1900 cd m(-12) , a luminance efficiency of about 3 cd A(-1) , and external quantum efficiencies exceeding 0.9 %.

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.

Indanthrone dye revisited after sixty years.

Indanthrone, an old, insoluble dye can be converted into a solution processable, self-assembling and electroluminescent organic semiconductor, namely tetraoctyloxydinaptho[2,3-a:2',3'-h]phenazine (P-C8), in a simple one-pot process consisting of the reduction of the carbonyl group by sodium dithionite followed by the substitution with solubility inducing groups under phase transfer catalysis conditions.

(Photo)physical Properties of New Molecular Glasses End-Capped with Thiophene Rings Composed of Diimide and Imine Units.

New symmetrical arylene bisimide derivatives formed by using electron-donating-electron-accepting systems were synthesized. They consist of a phthalic diimide or naphthalenediimide core and imine linkages and are end-capped with thiophene, bithiophene, and (ethylenedioxy)thiophene units. Moreover, polymers were obtained from a new diamine, N,N'-bis(5-aminonaphthalenyl)naphthalene-1,4,5,8-dicarboximide and 2,5-thiophenedicarboxaldehyde or 2,2'-bithiophene-5,5'-dicarboxaldehyde. The prepared azomethine diimides exhibited glass-forming properties. The obtained compounds emitted blue light with the emission maximum at 470 nm. The value of the absorption coefficient was determined as a function of the photon energy using spectroscopic ellipsometry. All compounds are electrochemically active and undergo reversible electrochemical reduction and irreversible oxidation processes as was found in cyclic voltammetry and differential pulse voltammetry (DPV) studies. They exhibited a low electrochemically (DPV) calculated energy band gap (Eg) from 1.14 to 1.70 eV. The highest occupied molecular orbital and lowest unoccupied molecular orbital levels and Eg were additionally calculated theoretically by density functional theory at the B3LYP/6-31G(d,p) level. The photovoltaic properties of two model compounds as the active layer in organic solar cells in the configuration indium tin oxide/poly(3,4-(ethylenedioxy)thiophene):poly(styrenesulfonate)/active layer/Al under an illumination of 1.3 mW/cm2 were studied. The device comprising poly(3-hexylthiophene) with the compound end-capped with bithiophene rings showed the highest value of Voc (above 1 V). The conversion efficiency of the fabricated solar cell was in the range of 0.69-0.90%.

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.

Optical properties of unsymmetrical azomethines with one imine bonds.

We have explored the photoluminescence (PL) and electronic properties, that is, orbital energies and resulting energy gap calculated theoretically by density functional theory (DFT) of four unsymmetrical (UAz1-UAz4) azomethines. All of the investigated compounds exhibited mesomorphic behavior. The photoluminescence studies have shown that molecular structure of the imines influenced both the PL properties and HOMO-LUMO levels of azomethines. Azomethines emitted violet, blue or green light. The effect of excitation wavelength and concentration on the PL properties has been detected as well. Unsymmetrical imine UAz3 posses carbazole unit exhibited lower both HOMO and LUMO energies compare to others investigated azomethines. Additionally, azomethines were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Two unsymmetrical imines (UAz2 and UAz3) exhibited irreversible oxidation behavior. The HOMO level of the compound with ethylcarbazole (UAz2) moiety was observed at -5.22 eV, while for the UAz3 with phenoxybiphenyl unit was found at -5.64 eV. The data obtained by theoretical calculation using DFT method was very similar to the results obtained by electrochemical measurements.