Theoretical investigations on the modulation of the polymer electronic and optical properties by introduction of phenoxazine

The color purity and efficiency of polyfluorene-based blue-emitting polymers is often compromised by long wavelengths, green emission bands and the charge injection difficulties. The incorporation of the phenoxazine units has been proved to significantly enhance the hole injection and charge carrier balance and at the same time efficiently suppress the keto defect emission. In this contribution, we apply quantum-chemical techniques to investigate poly(10-methylphenoxazine-3,7-diyl) (PPOZ) and its fluorene copolymer poly[(10-methylphenoxazine-3,7-diyl)-alt-2,7-(9,9-dimethyl-fluorene)] (PFPOZ), and gain a detailed understanding the influence of phenoxazine units on the electronic and optical properties of fluorene derivatives. The outcomes show that the highly non-planar conformation of phenoxazine ring in the ground state preclude sufficiently close intermolecular interactions essential to forming aggregates or excimers. Furthermore, the HOMO energies lift about 0.6 eV and thus the IPs decrease about 0.6 eV in PFPOZ, suggesting the significant improved hole-accepting and transporting abilities, due to the electron-donating properties of phenoxazine ring, which results in the enhanced performances in both efficiency and brightness compared with pristine polyfluorene.