Effect of conjugation and aromaticity of 3,6 di-substituted carbazoles on triplet energy and the implication of triplet energy in multiple-cyclic aromatic compounds

Effects of carbazolyl and diphenylamino substituents bearing methoxy groups on the performance of hole-transporting materials in OLEDs

Newly designed and synthesized derivatives of pentaphenylbenzene with methoxy-substituted carbazolyl or diphenylamino moieties were investigated to estimate their applicability as hole transport materials. Both the compounds exhibit high thermal stability. The intramolecular charge transfer is blocked for the film of the compound containing diphenylamino groups. The intermolecular charge transfer is induced in the film of carbazolyl-containing compound. The derivative of pentaphenylbenzene and diphenylamine exhibits higher hole drift mobility (2.4·10-3 cm2/V·s at the electric field of 5.5·105 V/cm) and by 0.1 eV lower ionization potential than the carbazolyl-containing compound. Both the compounds were utilized as hole-transporting materials in a series of organic light emitting diodes (OLEDs) based on of thermally activated delayed fluorescence. With the maximum values of external quantum efficiency of 25.9 % and power efficiency of 43.4 lm/W, OLEDs containing the layers of the synthesized compounds outperformed the device based on TCTA by 4 %, without the change in spectral properties. Variable angle spectroscopic ellipsometry revealed the moderate average roughness of the films of the compound deposited by the thermal vacuum evaporation technique with an arithmetic mean deviation of not more than 0.8 nm. The prominent hole transport characteristics of the compounds make them good candidates for utilization in optoelectronic devices.

Unveiling two antiaromatic s-indacenodicarbazole isomers with tuneable paratropicity

Linear and curved antiaromatic s-indacenodicarbazole isomers were synthesized and characterized to show tuneable strength of s-indacene paratropicity, as analyzed by NICS(1)zz and ACID (ring-current) calculations. The curved isomer showed a...

Rational designs of structurally similar TADF and HLCT emitters with benzo- or naphtho-carbazole units as electron donors

Structurally similar D–A type molecules with the combination of benzo- or naphtho-carbazole units as electron donors and tunable electron acceptors with different electron-withdrawing ability are designed to realize HLCT and TADF emissions.

Relating molecular descriptors to frontier orbital energy levels, singlet and triplet excited states of fused tricyclics using machine learning

Fused tricyclic organic compounds are an important class of organic electronic materials. In designing molecules for organic electronics, knowing what chemical structure that be used to tune the molecular property is one of the keys that can help to improve the material performance. In this research, we applied machine learning and data analytic approaches in addressing this problem. The energy states (Lowest Unoccupied Molecular Orbital (HOMO), Highest Occupied Molecular Orbitals (LUMO), singlet (E_s) and triplet (E_T) energy) of more than 10 thousand fused tricyclics are calculated. Corresponding descriptors are also generated. We find that the Coulomb matrix is a poorer descriptor than high-level descriptors in a multilayer perceptron neural network. Correlations as high as 0.95 is obtained using a multilayer perceptron neural network with Mean Absolute Error as low as 0.08 eV. The descriptors that are important in tuning the energy levels are revealed using the Random Forest algorithm. Correlations of such descriptors are also plotted. We found that the higher the number of tertiary amines, the deeper are the HOMO and LUMO levels. The presence of NN in the aromatic rings can be used to tune the E_S. However, there is no single dominant descriptor that can be correlated with the E_T. A collection of descriptors is found to give a far better correlation with E_T. This research demonstrated that machine learning and data analytics in guiding how certain chemical substructures correlate with the molecule energy states.

The impact of phenyl–phenyl linkage on the thermodynamic, optical and morphological behavior of carbazol derivatives

The impact of structural differentiation between phenylcarbazoles (PhC, mCP, CBP, TCB) and phenylamines (TPA, BDB, TPB, TDAB) on the phase equilibria, optical spectrum, band gap, and thin-film morphology is evaluated and discussed. The carbazolyl units lead to a lower electronic conjugation contributing to a wide band gap when compared with the diphenylamine analogs. The fusion and sublimation equilibria indicate that entropic contribution is the key factor for the distinguished melting behavior and solid-phase volatility between phenylcarbazole derivatives and phenylamine analogs. The molecular differentiation between the two classes of compounds is not reflected in the crystal packing and intermolecular interactions. However, compared with the diphenylamino groups, the incorporation of carbazolyl moieties contributes to a less flexible molecule. Moreover, the results evidence that intermolecular bonding disruption along the fusion transition is more extensive for phenylamine derivatives. Due to the asymmetric nonplanar structure, mCP is characterized by a ratio of {T_g/T_m ≈ 3/4} while the more symmetric CBP and TCB molecules display ratios closer to {T_g/T_m ≈ 2/3}. Vapor-deposited thin films of mCP, CBP, and TCB are amorphous and their morphology is highly dependent on the substrate roughness. The lower flexibility of nonplanar phenylcarbazoles induces the formation of a glassy state due to the harder packing mechanism leading to the lower ability of the crystallization process.

The phenyl–phenyl linkage in N-phenylcarbazoles contributes to several optical, structural, thermodynamic and morphological changes.

Molecular engineering of pyrene carbazole dyes with a single bond and double bond as the mode of linkage

Both carbazole and pyrene are electron-rich aromatic systems and are expected to be potential donors when used in push–pull dye architecture in the field of DSSC.

Synthesis, Anti-Cancer and Anti-Migratory Evaluation of 3,6-Dibromocarbazole and 5-Bromoindole Derivatives

In this study, a new series of N-alkyl-3,6-dibromocarbazole and N-alkyl-5-bromoindole derivatives have been synthesized and evaluated in vitro as anti-cancer and anti-migration agents. Cytotoxic and anti-migratory effects of these compounds were evaluated in MCF-7 and MDA-MB-231 breast cancer cell lines and an insight on the structure-activity relationship was developed. Preliminary investigations of their anti-cancer activity demonstrated that several compounds have moderate antiproliferative effects on cancer cell lines with GI50 values in the range of 4.7-32.2 µM. Moreover, carbazole derivatives 10, 14, 15, 23, and 24 inhibit migration activity of metastatic cell line MDA-MB-231 in the range of 18-20%. The effect of compounds 10, 14, and 15 in extension of invadopodia and filopodia was evaluated by fluorescence microscopy and results demonstrated a reduction in actin-based cell extensions by compounds 10 and 15.

Effect of Exocyclic Substituents and π-System Length on the Electronic Structure of Chichibabin Diradical(oid)s

The ground state (GS) of Chichibabin's polycyclic hydrocarbons (CPHs) can be singlet [open- or closed-shell (OSS or CS)] or triplet (T), depending on the elongation of the π-system and the exocyclic substituents. CPHs with either a small singlet-triplet energy gap (ΔE ST) or even a triplet GS have potential applications in optoelectronics. To analyze the effect of the size and exocyclic substituents on the nature of the GS of CPHs, we have selected a number of them with different substituents in the exocyclic carbon atoms and different ring chain lengths. The OPBE/cc-pVTZ level of theory was used for the optimization of the systems. The aromaticity of the resulting electronic structures was evaluated with HOMA, NICS, FLU, PDI, Iring, and MCI aromaticity indices. Our results show that the shortest π-systems (one or two rings) have a singlet GS. However, systems with three to five rings favor OSS GSs. Electron-withdrawing groups (EWGs) and aromatic substituents in the exocyclic carbons tend to stabilize the OSS and T states, whereas electron-donating groups slightly destabilize them. For CS, OSS, and T states, aromaticity measures indicate a gain of aromaticity of the 6-membered rings of the CPHs with the increase in their size and when CPHs incorporate EWGs or aromatic substituents. In general, the CPHs analyzed present small singlet-triplet energy gaps, and in particular, the ones containing EWGs or aromatic substituents present the smallest singlet-triplet energy gaps.

Impact of heteroatoms (S, Se, and Te) on the aromaticity of heterocirculenes

Computations reveal the structural and energetic aspects of aromaticity in heterocirculenes.