Tuning spectral properties of fullerenes by substitutional doping

We propose a substitutional doping approach to achieve tunable optical properties from fullerenes. Taking C₆₀ as an example and using time-dependent density functional theory, we compute the absorption spectra of heterofullerenes C_60-n-mN_nB_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 C59HN, we discuss the effect of organic functionalization, which is needed for device fabrication, on optical properties.