Theoretical design of blue emitting materials based on symmetric and asymmetric spirosilabifluorene derivatives

Abstract

Equilibrium ground state geometry configurations and their relevant electronic properties of four experimentally reported asymmetric spirosilabifluorene derivatives are calculated by the HF(DFT)/6-31G(d) method. Their excited state geometries are investigated using the CIS/6-31G(d) method. The absorption and emission spectra are evaluated using the TD-B3LYP/6-31G(d) and TD-PBE0/6-31+G(d) levels both in gas phase and CHCl3 solvent. Our results show an excellent agreement with the experimental data on their optical properties. To predict the substitution effect, the H/R (R = –NO2, –CN, –NH2 and –OCH3) substituted symmetric and asymmetric spirosilabifluorene derivatives are also investigated, and the optical properties of H/R substituted derivatives are predicted in gas phase and CHCl3 solvent. In comparison with the parent compound, significant red-shift is predicted for the emission spectra of the di-substituted symmetric derivatives with –NH2 (96 nm), –OCH3 (61 nm) and the push–pull (containing both –NH2 and –NO2) derivative (56 nm). It is found that the performance and the optical properties of these derivatives can be improved by adding push–pull substitutents. The largest change in the electronic and optical properties of this system can be obtained upon symmetric di-substitution among mono-, di-, tri- and tetra-substitutions.