Investigation of structural and optical characteristics of regioisomerically pure 1,7-perylene diimide: Experimental and density functional approaches

Abstract

In this paper, our work is focused on the synthesis, separation, and characterization of regioisomerically pure bay-substituted perylene diimide (PDI) derivative. We have utilized soxhlet extraction for the first time to separate 1,6,7-tribromo regioisomer and unreacted perylene dianhydride from 1,6 and 1,7 dibromo regioisomers followed by their separation using repetitive recrystallization. The structure of regioisomerically pure 1,7- bis (di-methoxy phenoxy) PDI encapped with silatrane (1,7- PDIST) was characterized using spectroscopic techniques and the equilibrium geometry was determined using B3LYP and WB97XD hybrid functionals under Density Functional Theory (DFT) framework. Further, Natural Bond Orbital (NBO) analysis was performed on the optimized structure in order to gain an understanding of charge transfer within the molecule. 1,7-PDIST with di-methoxy phenoxy group at the core was synthesized to evaluate the effect of the electron donor group at the bay position on the photophysical properties of PDI. The optical properties of the dye were evaluated experimentally and the results were corroborated by DFT calculation which demonstrated the significant effect of the dimethoxy phenoxy group at the bay position is due to the electron-donating nature of the group. Imidization via the silatrane can work as an anchoring group making PDI derivatives suitable candidates for organic electronic applications. Additionally, the solubility, optical and thermal features of dye have been discussed in detail. The dye was utilized in a dye sensitized solar cell (DSSC) which exhibited typical on-off photosensitive response in the transient current analysis.

Keywords

• Organic electronics
• n-type symmetrical PDIs
• Silatrane
• Fluorescence
• DFT
• Bay substituted PDIs