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The control of the doping ratio of a blue‐emitting matrix by an orange emitter with high accuracy still remains very challenging in the development of reproducible white organic light‐emitting diodes (WOLEDs). In this work, the development of an organophosphorus dopant that presents a high doping rate in order to reach white emission is reported. The increase of the doping rate has a small impact on the CIE co‐ordinates and on the EQE. These results are very appealing towards the development of “easy‐to‐make” WOLEDS.

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Keeping in view the possible applications of singlet open-shell molecules as semiconductors, non-classical derivatives of the heterocyclic rings benzobis(thiadiazole) (BBT) and its positional isomer thiadiazolothienopyrazine (TTP) are characterized using DFT methodologies. M06-2X, B3LYP and BHandHLYP functionals were used to optimize the geometries and estimate the vertical transition energies. It is observed that unlike the BHandHLYP functional (50% exchange), which gives rise to spin-contaminated solutions for all molecules in the series, M06-2X (54% exchange) affords a wavefunction either with no instability or negligible instability for most of the molecules. The results are compared with the earlier reported experimental data and those obtained herein using the spin-flip (SF)-5050 method. It is found that B3LYP does not fare well while on the other hand the M06-2X and SF-50-50 are in good agreement with the experimental results. It is seen that M06-2X TD-DFT for the molecules can be carried out without major spin contamination and also that the more time-consuming CI can be avoided for the calculation of transition energies. The biradical nature of the molecules is estimated by the singlet-triplet gap. Intramolecular charge transfer is calculated. It is found that the ring substituents donate charge in the ground state, creating a zwitterionic structure. Thus the substituents play an interesting dual role, decreasing the stability of the molecule by increasing the biradical character (small HOMO-LUMO gap), and stabilization of this ground state by intramolecular charge transfer.

Main factors responsible for the red to near infrared (NIR) absorption of the benzobis(1,2,5‐thiadiazole) (BBT) derivatives have been investigated using high level computational studies. These molecules with NIR emission are of importance due to the recent reports of possible role in NIR organic light emitting diodes (OLED) development. The electronic structure has been determined using closed‐shell/open‐shell DFT methods (B3LYP and BHandHLYP). The wavefunction stabilities of these BBT derivatives have been tested. We notice that using the BHandHLYP functional, the wave function becomes instable though large HOMO–LUMO gaps (HLG) are obtained. On the other hand a stable wavefunction is obtained using the B3LYP functional but the HLG is small. The B3LYP HLG is in good agreement with the available experimental data. Nevertheless results from both functionals indicate a possible LUMO occupation/biradicaloid character (BRC). We calculated the BRC for all the molecules using different methods and observed that these molecules have a large BRC which correlates well with excitation energies. Larger the BRC smaller the excitation energy. Charge transfer based on Mulliken charges of both ground and excited state are obtained from high level SAC/SAC‐CI studies. We carried out the VB studies of the unsubstituted BBT to predict the relative weights of the individual Lewis structures to the resonance picture. It is concluded that a more general description which include the zwitterionic and biradical structures are necessary for these molecules and not just simple donor–acceptor–donor (D–A–D) structures as suggested in the literature. Copyright © 2011 John Wiley & Sons, Ltd.

A simple two-step design strategy has been developed for the synthesis of a large variety of a new class of tyrosine-based aromatic (Ph or Pyr) bridged cyclodepsipeptides (tyrosinophanes). The design is flexible with respect to the size of the ring and the nature of the bridging unit and permits the incorporation of a variety of amino acid residues inside or outside or both inside and outside the ring as illustrated here with the preparation of tyrosine-based macrocycles with aromatic (Ph or Pyr), cage-like alicyclic (adamantane) or simple polymethylene bridging units in ring sizes varying from 26-membered to 78-membered and containing leucine residues as part of the ring or as pendants on the exterior or both inside and outside the macrocyclic ring. (1)H NMR, FT-IR, and CD studies have indicated open-ring structures for these macrocycles. A noteworthy feature of the strategy is the formation of the 1 + 1 + 1 + 1 catenane arising from the interlocking of sebacoyl-bridged tyrosine rings. The potential of tyrosinophanes to serve as simple aromatic hosts in the study of pi-cation type interactions was illustrated with Pyr-bridged macrocycles (6b-8b) using N-methylacridinium hexafluorophosphate as the pyridinium guest. The K(assoc) value with 6b was found to be 8.95 x 10(3) M(-)(1).

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