Effect of the position of substitution on the electronic properties of nitrophenyl derivatives of fulleropyrrolidines: Fundamental understanding toward raising LUMO energy of fullerene electron-acceptor

A series of substituted para-, meta- and ortho-nitrophenyl derivatives of fulleropyrrolidine were synthesized to investigate the effects of the position of substitution on electronic properties by using steady-state absorption and fluorescence spectra, combined with DFT calculations. The results confirmed that the position of substitution has little effect on absorption and fluorescence spectra, whereas a significant effect was observed on their LUMO energy levels. The theoretical calculations revealed that the LUMO energy of the ortho-nitrophenyl substituted derivative was increased 0.1 eV above those of para- and meta-substitution. The prominent effect of ortho-substitution was attributed to the through-space orbital interaction between spatially closed electron-withdrawing nitro group and fullerene cage. These findings could provide fundamental insights in raising LUMO levels of C60-based electron acceptor materials and an alternative strategy to increase open circuit voltage Voc in polymer solar cells.

Graphical abstractThe through-space orbital interaction between spatially closed ortho-nitrophenyl substituent and fullerene cage efficiently raised the LUMO energy level of fullerene electron-acceptor.Figure optionsDownload full-size imageDownload as PowerPoint slide