Theoretical Investigations On The Multifunctional Organic Light-Emitting Materials

In the past decade, organic electroluminescent materials have become a fascinating field in the world for their wide range of applications, such as industrial production, military affairs, and medical treatment, etc. Organic electroluminescent devices have such advantages as low-voltage driving, high luminosity, high efficiency, low cost and large-area color display which can be realized. Thus there has been great interest in investigating organic electroluminescent materials and devices.In this paper, from the point of view of the molecular design, we systematically studied the molecules with the basic framework including boron and nitrogen atoms by DFT, TDDFT, HF, and CIS quantum-chemical methods and obtained the properties of the ground state and the lowest excited state conformations, HOMOs, LUMOs, energy gaps, ionization potentials, electronic affinities, reorganization energies, absorption and emission spectra. The theoretical studies show that the electronic and optical properties of the light-emitting materials can be greatly modulated and improved by modifying chemical structures. Also, it is anticipated that it can help to understand the microcosmic electroluminescent mechanism and contribute to orientate the synthesis and design of the novel light-emitting materials by exploring the structure-property relations.The following is the main results:1. Three molecules, which have the same carbazolyl donor and B(mesityl)2 acceptor group as well as differentπ-conjugated bridges, have been chosen as the objects. The optical and electronic properties of these compounds are closely related to theirπ-conjugated bridge. The results show that these compounds show great potential for application in OLEDs as hole and electron transport/injection blue or green materials.2. Seven compounds, which are the four-coordinate boron complexes containing the mixed phenol-pyridyl group, have been studied by theoretical calculation. It can be obtained a wide variety of useful OLEDs via tuning the substitution. The results show that the boron atom mainly plays the role of a stent or bridge in the studied polydentate chelating ligands. Compounds 1-5, and 6 and 7 can be used as bifunctional (emitter, electron-transport) and tri-functional (emitter, electron-transport, and hole-transport) molecules in OLEDs, respectively. The calculated emission spectra of the seven studied molecules can almost cover the full UV-vis range (from 447.4 to 649.3 nm). They have excellent properties as multifunctional OLEDs.3. A series of triphenyl amino-based compounds were calculated, including new designed two molecules. The results show that they can function as charge transport materials and emitters with high efficiency and stability. Compounds 1 and 2 have improved electroluminescent properties under keeping the emission wavelength in blue region and unchanged molecular shape and weight in contrast to BNPB and NPB. We hope that our theoretical study can shine some light on the fabricating and designing bifunctional and multifunctional OLEDs with excellent properties.4. A series of dipolar amine- and trivalent boron-based bifunctional or multifunctional compounds has been studied by theoretical calculation. The introduction of thiophene group, anthracene group, and N=N inπ-conjugated bridge enhance the ability of the electron injection, and make the HOMO-LUMO gaps become narrow, resulting the spectra red-shifted. Compounds 1-4 can be used as blue or green OLEDs with the ability of both hole and electron transport/injection. Compounds 5 and 6 can be used as ET and HT materials, respectively.