Thienopyrrolo[3,2,1-jk]carbazoles: Building Blocks for Functional Organic Materials.

The facile preparation of three regioisomeric thienopyrrolo[3,2,1-jk]carbazoles applying a convenient C-H activation approach is presented. The incorporation of thiophene into the triarylamine framework significantly impacted the molecular properties in comparison to the analogous indolo[3,2,1-jk]carbazole scaffold. Dependent on the exact substitution pattern, the absorption onsets of the new materials are shifted toward slightly higher wavelengths compared to the analogous indolo[3,2,1-jk]carbazole, whereas the emission maxima of the sulfur derivatives is shifted from 375 to 410 nm. In analogy, the HOMO-LUMO energy gap of the thienopyrrolo[3,2,1-jk]carbazoles is reduced compared to indolo[3,2,1-jk]carbazole. Therefore, the developed thienopyrrolo[3,2,1-jk]carbazoles enrich the family of triarylamine donors and constitute a novel building block for functional organic materials.

Azaindolo[3,2,1-jk]carbazoles: New Building Blocks for Functional Organic Materials.

The preparation and characterization of 12 azaindolo[3,2,1-jk]carbazoles is presented. Ring-closing C-H activation allowed for the convenient preparation of six singly and six doubly nitrogen-substituted indolo[3,2,1-jk]carbazole derivatives in which ten of the materials have not been described in the literature before. The detailed photophysical and electrochemical characterization of the developed materials revealed a significant impact of the incorporation of pyridine-like nitrogen into the fully planar indolo[3,2,1-jk]carbazole backbone. Furthermore, the nitrogen position decisively impacted intermolecular hydrogen bonding and thus the solid-state alignment. Ultimately, the versatility of the azaindolo[3,2,1-jk]carbazoles scaffold makes this class of materials an attractive new building block for the design of functional organic materials.

A novel selenoalkenyl-isoxazole based donor-acceptor nonlinear optical material.

The structure property relationships of untwinned enantiomorphic Z-(methylseleno)alkenyl-substituted phenyl-isoxazole and its isostructural triazole congener both crystallizing in the P212121 space group were investigated with respect to UV/vis absorption, thermal behaviour, and second harmonic generation ability. Differential scanning calorimetry revealed a significantly higher melting point of the novel isoxazole compound compared to the triazole derivative and therefore a broader thermal application window. The SHG efficiency of the isoxazole derivative is approximately two thirds the value of the triazole compound and approximately 27 times higher than potassium dihydrogen phosphate. Thus, the developed molecular scaffold represents an interesting novel type of nonlinear optical (NLO) chromophore.

Charge-transfer states in triazole linked donor-acceptor materials: strong effects of chemical modification and solvation.

A series of 1,2,3-triazole linked donor-acceptor chromophores are prepared by Click Chemistry from ene-yne starting materials. The effects of three distinct chemical variations are investigated: enhancing the acceptor strength through oxidation of the sulphur atom, alteration of the double bond configuration, and variation of the triazole substitution pattern. A detailed photophysical characterization shows that these alterations have a negligible effect on the absorption while dramatically altering the emission wavelengths. In addition, strong solvatochromism is found leading to significant red shifts in the case of polar solvents. The experimental findings are rationalized and related to the electronic structure properties of the chromophores by time-dependent density functional theory as well as the ab initio algebraic diagrammatic construction method for the polarization propagator in connection with a new formalism allowing to model the influence of solvation onto long-lived excited states and their emission energies. These calculations highlight the varying degree of intramolecular charge transfer character present for the different molecules and show that the amount of charge transfer is strongly modulated by the conducted chemical modifications, by the solvation of the chromophores, and by the structural relaxation in the excited state. It is, furthermore, shown that enhanced charge separation, as induced by chemical modification or solvation, reduces the singlet-triplet gaps and that two of the investigated molecules possess sufficiently low gaps to be considered as candidates for thermally activated delayed fluorescence.

Structure-Property Relationships in Click-Derived Donor-Triazole-Acceptor Materials.

To shed light on intramolecular charge-transfer phenomena in 1,2,3-triazole-linked materials, a series of 1,2,3-triazole-linked push-pull chromophores were prepared and studied experimentally and computationally. Investigated modifications include variation of donor and/or acceptor strength and linker moiety as well as regioisomers. Photophysical characterization of intramolecular charge-transfer features revealed ambipolar behavior of the triazole linker, depending on the substitution position. Furthermore, non-centrosymmetric materials were subjected to second-harmonic generation measurements, which revealed the high nonlinear optical activity of this class of materials.

1-Nitro-9H-carbazole.

In the title mol-ecule, C12H8N2O2, the nitro group is tilted slightly with respect to the carbazole moiety [angle between the least-squares planes = 4.43 (9)°]. In the crystal, the mol-ecules are connected via pairs of N-H⋯O hydrogen bonds into dimers with -1 symmetry. The dimers in turn are arranged into layers parallel to (10-1).

Isotypic crystal structures of 2,6-di-bromo-N,N-bis-(4-nitro-phen-yl)aniline and 2,6-di-chloro-N,N-bis-(4-nitro-phen-yl)aniline.

In the mol-ecules of the two isotypic title compounds, C18H11Br2N3O4 (I) and C18H11Cl2N3O4 (II), the tri-phenyl-amine N atoms show no sign of pyramidalization, with marginal displacements of the N atoms from the mean plane of the three connecting C atoms: 0.0058 (13) Šfor the Br compound (I) and 0.0074 (9) Šfor the Cl compound (II). In the crystals, mol-ecules are linked through C-H⋯O hydrogen bonds between phenyl rings and nitro groups and by X⋯O (X = Br, Cl) inter-actions, that are shorter than the sum of the van der Waals radii, leading to a three-dimensional network.

9-(4-Bromo-phen-yl)-9H-carbazole.

In the title mol-ecule, C18H12BrN, the 4-bromo-phenyl ring is inclined to the mean plane of the carbazole moiety (r.m.s. devation = 0.027 Å) by 49.87 (5)°. In the crystal, molecules stack along [001] and are linked by C-H⋯π interactions forming a corrugated two-dimensional network lying parallel to (100).

Solvatomorphism of 9,9'-[1,3,4-thiadiazole-2,5-diylbis(2,3-thiophendiyl-4,1-phenylene)]bis[9H-carbazole]: isostructurality, modularity and order-disorder theory.

During a systematic investigation of the crystallization behaviour of 9,9'-[1,3,4-thiadiazole-2,5-diylbis(2,3-thiophendiyl-4,1-phenylene)]bis[9H-carbazole] (I), six single crystalline solvates were obtained and characterized by X-ray diffraction at 100 K. The structure of the hemi-2-butanone (MEK) solvate contains two crystallographically independent molecules of (I) related by pseudo-inversion symmetry. The structure is polytypic and composed of non-polar (I) layers and polar solvent layers. It can be described according to an extended order-disorder (OD) theory with relaxed vicinity condition. The observed polytype is of a maximum degree of order (MDO). Layer triples of the second MDO polytype are shown by twinning by inversion. The mono-benzene and mono-toluene solvates are isostructural. Whereas the (I) layers are isostructural to those of the idealized description of the hemi-MEK solvate, the solvent layers are non-polar, resulting in a fully ordered structure. The toluene molecule is ordered, the benzene molecule features disorder. The (I) layers in the sesqui-dioxane and sesqui-benzene solvates are isostructural and unrelated to those in the hemi-MEK, mono-benzene and mono-toluene solvates. The solvent layers are isopointal in both sesqui-solvates, but the stacking differs significantly. The hemi-dideuterodichloromethane (DCM-d(2)) solvate is made up of two kinds of (I) rods, spaced by DCM-d(2) molecules. Rods of one kind are similar to analogous rods in the sesqui-dioxane and the sesqui-benzene solvates, whereas rods of the other kind are only remotely related to rods in the hemi-MEK solvate.

The phase transitions of 4-aminopyridine-based indolocarbazoles: twinning, local- and pseudo-symmetry.

The phase transitions and polymorphism of three 4-aminopyridine-based indolocarbazole analogues are analyzed with respect to symmetry relationships and twinning. Seven polymorphs were structurally characterized using single-crystal diffraction. 5NICz (the indolo[3,2,1-jk]carbazole derivative with the C atom in the 5-position replaced by N) crystallizes as a P21/a high-temperature (270 K) polymorph and as a Pca21 low-temperature (150 K) polymorph. Even though their space-group symmetry is not related by a group-subgroup relationship, the local symmetries of both belong to the same order-disorder (OD) groupoid family. Both are polytypes of a maximum degree of order and are twinned by point operations of the other polytype. 2NICz (C atom in the 2-position replaced by N) likewise crystallizes in a high-temperature (Pcca, 280 K) polymorph and a low-temperature (P21/c, 150 K) polymorph. Here, the space-group symmetries are related by a group-subgroup relationship. The low-temperature phase is twinned by the point operations lost on cooling. The crystal structure of bulk 2,5NICz (N-substitution at the 2- and 5-positions) was unrelated to 2NICz and 5NICz and no phase transition was observed. Isolated single crystals of a different polymorph of 2,5NICz, isotypic with 2NICz, were isolated. However, the analogous phase transition in this case takes place at distinctly higher temperatures (> 300 K).

Controlling excimer formation in indolo[3,2,1-jk]carbazole/9H-carbazole based host materials for RGB PhOLEDs.

Three novel materials (5CzICz, Cz2ICz and Cz3ICz), based on the indolo[3,2,1-jk]carbazole and 9H-carbazole building blocks, with high triplet energies (E T > 2.80 eV) and good thermal stability (T g > 101 °C) were synthesized, characterized and applied as host materials in PhOLED devices. In course of the preparation of the materials, an improved protocol for the synthesis of the indolo[3,2,1-jk]carbazole moiety has been developed. The careful molecular design of the title compounds allowed to avoid excimer formation of the indolo[3,2,1-jk]carbazole subunits in thin films. Therefore, the improved molecular design broadened the applicability of indolo[3,2,1-jk]carbazole host materials and significantly enhanced the efficiency of PhOLED devices based on these derivatives compared to previously reported indolo[3,2,1-jk]carbazole based compounds. Accordingly, employing the newly developed materials red (CEmax: 32.7 cd A-1, PEmax: 31.0 lm W-1, EQEmax: 20.4%), green (CEmax: 81.0 cd A-1, PEmax: 87.4 lm W-1, EQEmax: 21.5%) and blue (CEmax: 35.5 cd A-1, PEmax: 39.9 lm W-1, EQEmax: 18.0%) PhOLED devices with a remarkably low efficiency roll-off at 1000 cd m-2 (Cz2ICz - red: 5%; green: 0%; blue: 6%) were fabricated.

Crystal chemistry of trialkylsilyl-capped (3Z)-4-(methylthio)-3-penten-1-yne: polymorphism, twinning and ambiguity of order-disorder descriptions.

The crystallization behavior of trimethylsilyl-capped (3Z)-4-(methylthio)-3-penten-1-yne (1-TMS) and the triisopropylsilyl and tert-butyldimethylsilyl analogues (1-TIPS) and (1-TBDMS) was investigated. (1-TMS) crystallizes in the Sohncke space group P212121 with Z' = 1. (1-TIPS) exists as two polymorphs, both crystallizing in P\overline 1 with Z' = 2 independent molecules. Polymorph (I) is an order-disorder (OD) twin. Two interpretations in terms of M = 1 or M = 2 kinds of OD layers are possible, with different degrees of idealization. Polymorph (II) is fully ordered (non-twinned). Its structure can be derived from polymorph (I) by inverting the orientation of every second molecule. (1-TBDMS) (P\overline1, Z' = 2) is an OD twin, where the OD description is unambiguously in M = 1 kinds of layers.

Crystal chemistry of layered structures formed by linear rigid silyl-capped molecules.

The crystallization behavior of methylthio- or methylsulfonyl-containing spacer extended Z,Z-bis-ene-yne molecules capped with trimethylsilyl groups obtained by (tandem) thiophene ring fragmentation and of two non-spacer extended analogs were investigated. The rigid and linear molecules generally crystallized in layers whereby the flexibility of the layer interfaces formed by the silyl groups leads to a remarkably rich crystal chemistry. The molecules with benzene and thiophene spacers both crystallized with C2/c symmetry and can be considered as merotypes. Increasing the steric bulk of the core by introduction of ethylenedioxythiophene (EDOT) gave a structure incommensurately modulated in the [010] direction. Further increase of steric demand in the case of a dimethoxythiophene restored periodicity along [010] but resulted in a doubling of the c vector. Two different polytypes were observed, which feature geometrically different layer interfaces (non-OD, order-disorder, polytypes), one with a high stacking fault probability. Oxidation of the methylthio groups of the benzene-based molecule to methylsulfonyl groups led to three polymorphs (two temperature-dependent), which were analyzed by Hirshfeld surface d e/d i fingerprint plots. The analogously oxidized EDOT-based molecule crystallized as systematic twins owing to its OD polytypism. Shortening of the backbone by removal of the aryl core resulted in an enantiomorphic structure and a further shortening by removal of a methylthio-ene fragment again in a systematically twinned OD polytype.