“Push–pull” 1,8-naphthalic anhydride with multiple triphenylamine groups as electron donor

• Three new naphthalic anhydride compounds with linear triphenylamino oligomer were prepared.
• The enhanced electron donating ability of the donor leads to excited state changes from ICT state to electron transfer.
• Theoretical calculation reveals that a higher ICT states may responsible for the weak emission of 3.

In this paper, the “push–pull” molecules consisting of different number of triphenylamino groups and 1,8-naphthalic anhydride ring were designed and synthesized. The UV–vis absorption and emission spectra of these compounds were recorded. Along with the increase on the number of the electron donating triphenylamino groups, both the absorption and emission bands show significant red shift. More importantly, the fluorescence quantum yields drop sharply along with the increase on the number of triphenylamino groups. The molecular structure, the frontier molecular orbital energies and the energy gaps between the highest occupied molecular orbital (HOMO) and the lowest un-occupied molecular orbital (LUMO) were calculated with DFT method. The calculated results indicate that the connection of more electron donating triphenylamino groups in molecule caused a change for the first excited state from an intramolecular charge transfer (ICT) state to an intramolecular electron transfer state (ET). This change on the first excited state has led to the fluorescence quenching.