Structural and photophysical characterization of the small ultra-red fluorescent protein oleh Atanu Maiti, Cosmo Z. Buffalo, Saumya Saurabh, Felipe Montecinos-Franjola, Justin S. Hachey, William J. Conlon, Geraldine N. Tran, Bakar Hassan, Kylie J. Walters, Mikhail Drobizhev, W. E. Moerner, Partho Ghosh, Hiroshi Matsuo, Roger Y. Tsien, John Y. Lin, Erik A. Rodriguez