Tuning spectral properties of fullerenes by substitutional doping

We propose a substitutional doping approach to achieve tunable optical properties from fullerenes. Taking ${\mathrm{C}}_{60}$ as an example and using time-dependent density functional theory, we compute the absorption spectra of heterofullerenes ${\mathrm{C}}_{60-n-m}{\mathrm{N}}_n{\mathrm{B}}_m,$ and demonstrate that their optical gaps and first triplet energies can be tuned from the near-infrared up to the ultraviolet by tailoring the dopant numbers n and m. This is supported by experiment and suggests heterofullerenes as single-molecule fluorescent probes and as building blocks for the bottom-up assembly of tunable luminescent devices. For the example of ${\mathrm{C}}_{59}\mathrm{HN},$ we discuss the effect of organic functionalization, which is needed for device fabrication, on optical properties.