Theoretical Investigations On The Red Organic Light-Emitting Materials

For full-color displays, three primary colors, i.e., blue, green, and red light-emitting materials are required. Green and blue light-emitting materials have al-ready met the requirements for commercial application. However, the red light-emitting materials with high brightness and efficiency are scarce. Nowadays, the rapid developments of science and technology have greatly contributed to the devel-opment of computational chemistry. Theoretical calculations show that by chemical modification the physical properties of materials could greatly be improved.In this paper, we systematically investigated three types of red emitting materials, including porphyrin relatives with through-bond energy transfer character, oligomer with electron-deficient group, phenylamine substitued Ir compounds, by quantum chemistry methods, namely, DFT, TDDFT, TDHF, CIS methods. We systematically investigated the ground state and lowest excited state conformations, frontier molecu-lar orbital, ionization potential (IP), electronic affinities (EA), reorganization ener-gies(λ), absorption and emission spectra. The theoretical study is intended to establish the structure-photophysical property relationship for designing efficient red emitters for OLEDs. The following is the main results:1. A series of porphyrin relatives with through-bond energy transfer character is investigated. The calculated results show that the TB energy transfer character has been detected in some extent by the analyses of electronic structure, frontier molecu-lar orbital and electronic spectra. Moreover, the reasons for their high efficiency as red emitting materials have been revealed by the investigations of the ionization po- tential (IP), electron affinity (EA), reorganization energy (λ), and exciton binding en-ergy (Eb). After introducing the 2-[thiophen-2-yl]thiophene to porphyrin-ring, the electronic injection and transfer abilities of porphyrin relatives are greatly enhanced. 5?10?15?20-tetra(carbazole)porphyrin(TCP) and Zn-5?10?15?20-tetra(carbazole) or-phyrin (ZCP) have faster carrier injection and transport rate, better carrier transport balance, and relatively smaller exciton binding energy than experimental sythesized molecules, rendering great potential of these red emitting materials with high fluores-cence quantum yield in the development of red OLEDs.2. A series of fluorene-based oligomers containing 2-pyran-4-ylidene malononitrile (PM) unit is investigated. The calculated results the electronic structure and photoproperties have been greatly improved by PM unit. It is found that the in-troduction of thiophene and 2-methoxyphenol in this type of copolymers have low-ered the LUMO energy, lifted the HOMO energies, and narrowed HOMO-LUMO gaps. Furthermore, Among these compounds, {2-[2-{2-[5-(9H-Fluoren-3-yl)- thio-phen-2-yl]-vinyl}-6-(2-thiophen-2-yl-vinyl)-pyran-4-ylidene]-malononitrile}n has de-creased IP, increased EA, and decreasedλhole values, suggesting that it is a excellent red emitting materials with high charge injection and transportation.The effect of phenylamine chromophore on the structure, optical properties, charge injection as well as charge transport features of a series of iridium(III) com-plexes is investigated. Our calculation results indicate that the hole injection ability have been greatly altered by the aromatic amine units. By introducing the diphenyl-amine unit, the contribution of 5d orbital from Ir center to the HOMO of both the ground and triplet states is decreased. From the consideration of IP, EA,λ, the pa-ra-substituted derivative Ir-(g1')3 where g1'=N-(3-(2,3-dihydro-2-methylisoquinolin-1- yl)-4-methylphenyl)-N-phenyl benzenamine has great potential to serve as a high performance red triplet emitter.