Theoretical and experimental study on the electronic structure of distyrylnaphthalene-based conjugated oligoelectrolytes

Abstract

In this study the UV–Vis absorption and fluorescence spectroscopy as well as theoretical calculations have been applied to describe electronic structure of the distyrylnaphthalene (DSNN) chromophore. In the theoretical description of the DSNN chromophore of the D-π-A-π-D scheme, the concept of the two valence bond state model for donor-acceptor substituted conjugated systems was adopted. Two mesomeric (resonance) structures were considered: the neutral (aromatic-like) one and charge-separated (quinoid-like) form and these structures were optimized with the use of semi-empirical PM3, PM6 and DFT methods. It has been suggested that the ground state geometry of DSNN chromophore is mainly dominated by the aromatic-like form, which is nonplanar and is characterized by the relatively large BLA parameter. The quinoid-like charge separated form, proposed in the applied two valence bond state model, was characterized by nearly zero value of the BLA parameter, the lowest transition energy and the large transition dipole moment value. The TD DFT geometry optimization of the first excited singlet state revealed that the S0→S1 excitation leads to the planarization of the DSNN backbone as well as to the quinoidation of the aromatic-like structure and confirmed the ICT for the relaxed first excited singlet state. The results obtained in this study are important for understanding of the properties of DSNN and are essential for rational design of the DSNN based conjugated electrolytes with pre-defined optical and conductive properties.