Theoretical Investigations On The Organic Oligomer And Metal Complexes Light-Emitting Materials

Recently, researchers focus on developing and designing new luminescent devices with high efficiency, high stability and high brightness. Electroluminescent materials, especially transition metal complexes, have been used in almost all fields, e.g. industrial production, military affairs and medical treatment, due to their merits of high efficiency of luminescence, high stability, long luminescent lifetime, single color and high brightness, etc.In this paper, from the point of view of the molecular design, DFT, HF, CIS and TDDFT have been employed to investigate the optical and electronic properties of a series of organic oligomers and metal complexes. The aim is providing structure-property relations in electroluminescent materials and orientating the synthesis and design of novel light-emitting materials.The main results are summarized here:1. A series of arene/fluoroarene-thiophene co-oligomers has been investigated. The fluorophenyl-substitution in the oligomer resulted in decreased LUMO energies, and then greatly improved the electron-injection ability. The optical and electronic property of the oligomers is influenced by the sequential variation of arene-thiophene fragment positioning and thiophene core. The rational structural tunings greatly improve the optoelectronic property in the oligomers.2. Investigation on oligofluorenylthiophenes and fluoroarene-thiophene has been performed. With the thiophene chain length increasing, charge injection and transport balance are improved in the oligomers. The studied oligomers, particularly the designed molecule, can be used in OLEDs as excellent ambipolar materials.3. A series of spirobifluorene derivatives have been investigated. By the rational introduction of electron-donating and electron-accepting moieties, charge injection and transport balance are improved and blue-light-emitting materials have been obtained.4. Investigation on the chalcogen-bridged mercury compounds has been performed. The large metal composition in the frontier molecular orbitals can bring about high quantum efficiency. The conjugation extent increases in the metal complexes and the absorption and emission spectra exhibit red shifts. The much smallerλhole andλelectron of 6h leads to the improved hole and electron transfer rate.5. The investigation of the doubly ortho-linked quinoxaline/diphenylfluorene hybrids has been performed. The molecules 1b-1d show excellent HT (hole-transport) and ET (electron-transport) abilities and charge injection property. The studied materials show different emission colors varying from 436.11 to 715.47 nm.6. We have investigated theoretically a series of IrIII complexes with various main group substituents on the phenyl moiety of ppy. A new method toward the switch of charge-transfer character and emission color tuning of IrIII complexes via the facile variation of electron-withdrawing moieties is demonstrated. Improved optical and electronic properties, e.g. good charge transfer balance performance of these complexes were harvested.7. Theoretical investigation on the four Pt(II) and Ir(III) complexes was performed. The increase in the number of TPA in molecules increases the conjugated extent and thereby leads to red-shifts in absorption and emission spectra. Pt-a, Pt-b and Ir-b have nice hole-transporting property and Ir-a has good ambipolar charge-transfer ability, which can serve as powerful candidates for OLEDs.