A comparative study on the optical properties of indenofluorene and indenopyrazine

As a core structure for a new functional dye which can be used as materials for electronic devices such as field-effect transistors or light-emitting diodes, indenofluorene and indenopyrazine have been studied. CIS/6-31G* level was applied to optimize the geometry of the first excited state used to calculate the emission spectrum. Their UV absorption and PL emission spectra were calculated by using time-dependent density functional theory (TDDFT) method at B3LYP/6-31G* level. The influence of THF solvent was considered using polarized continuum model TDDFT (PCM-TDDFT) method as well. PCM-TDDFT results are red-shifted by about 10 nm in comparison to the corresponding predicted absorption and emission maximum in vacuum. In PCM-TDDFT results, the absorption maxima of indenopyrazine were red-shifted by about 25 nm compared to those of indenofluorene. This spectral shift, induced by the nitrogen atoms in the pyrazine ring of indenopyrazine, are explained by the analysis of electronic structures of indenofluorene and indenopyrazine and the atomic contributions of the pyrazine nitrogen atoms to the frontier molecular orbital of indenopyrazine.