Structural, electronic, and optical properties of doubly ortho-linked quinoxaline/diphenylfluorene hybrids

Abstract

The optical and electronic properties of spiro-fluorene-dibenzosuberene[d](1,4-bis(4-t-butylphenyl)quinoxaline) 1a, spiro-fluorene-dibenzosuberene[d](1,4-bis(4-methoxyphenyl)quinoxaline) 1b, spiro-fluorene-dibenzosuberene[d](1-(4-(N,N-diphenylamino)-phenyl)-quinoxaline) 1c, spiro-fluorene-dibenzosuberene[d](1,4-bis(methylphenylamino)quinoxaline) 1d, spiro-fluorene-dibenzosuberene[d](1,4-bis(methyl-(4-methylphenyl)amino)quinoxaline) 1e, spiro-fluorene-dibenzosuberene[d](1,4-bis(methyl-(4-methoxyphenyl)amino)quinoxaline) 1f, 5,8-bis-(4-methoxy-phenyl)-2,3-diphenyl-quinoxaline 1, and N,N,N',N'-tetraphenyl- 5h-dibenzo[a,d]cycloheptene-3,7-diamine 2 were investigated theoretically in this paper. The doubly ortho-linked quinoxaline/diphenylfluorene hybrids 1a–1f show great potential as bipolar materials for the design of optimized organic light-emitting diodes (OLEDs). Density functional theory (DFT) and ab initio HF were employed to study the geometric and electronic structures of these molecules in the ground state, and ab initio CIS were used to investigate the lowest singlet excited states. The radiative lifetime (τ) and the maximal absorption/emission wavelength of these molecules were calculated within time-dependent DFT (TDDFT). The results show that the LUMO energies of the bipolar molecules 1a–1d are all lower than those of 1 and 2, consequently, the electron-accepting abilities of 1a–1d are greatly improved. The HOMO energies of 1c–1f are all higher than those of 1 and 2, suggesting that the hole-creating abilities of 1c–1f become better. Also, the results reveal that the HOMO and LUMO energies, energy gaps, IP, EA, as well as the maximal absorption/emission spectra can be tuned feasibly by changing the C5- and C8-substituents in the quinoxaline backbone of these molecules. As expected, these materials show different emission spectra varying from 436.11 to 715.47 nm. Copyright © 2010 John Wiley & Sons, Ltd.