Efficient tuning of optoelectronic properties of 1,6- and 1,7-disubstituted perylene diimides: agreement between theory and experiment.

In the literature, PDIs have been shown to demonstrate extensive applications in the area of organic electronics due to their ability to act as n-type semiconductors. PDIs have been applied in a wide range of electronic devices, including energy storage devices. To fit in these applications, we have modified the valine-terminated PDI core by substituting groups, viz. phenoxy, 4-methoxy phenoxy, and 3,4-dimethoxy phenoxy groups, at bay positions to fine-tune their HOMO-LUMO levels. In this paper, a series of conjugation-extended 1,7-, 1,6- and 1,6,7-regioisomers of Val-PDIs were synthesized, and 1,6,7-PDIs were removed by utilizing the Soxhlet extraction technique used for the first time. The 1,7- and 1,6-PDIs were separated by repeated crystallization and their structural characterization was performed using FTIR, ¹H NMR, 13C NMR, and HRMS. Further, the structures of as-synthesized PDIs were optimized by DFT calculations using the B3LYP approach with a 6-31+G(d,p) basis set, and the electronic transitions were visualized by analyzing natural transition orbitals (NTO). The photophysical properties of the highly soluble bay-substituted PDIs were evaluated using UV-Visible and fluorescence spectroscopic techniques in organic solvents ranging from non-polar to polar. Furthermore, their relative polarities in the ground vs. excited state were determined by employing the Lippert-Mataga relations. The electrochemical investigations of PDIs were done using cyclic voltammetry to evaluate their redox behavior. In addition to their unique structural relationship, 1,7- and 1,6-regioisomers revealed intriguing optoelectronic properties. Finally, symmetric supercapacitors (SSCs) were developed by exploiting the regioisomerically pure 1,7- and 1,6-disubstituted PDIs as electrode materials. The as-fabricated PDIs/GF electrodes were optimized in a two-electrode SC device given their electrochemical performance. Two of the PDIs, viz. M1 and D1, demonstrated good results of specific capacitances, i.e. 59.41 and 23.60 Fg-1 respectively, in the SSC devices. [ABSTRACT FROM AUTHOR]