Controlling the excited electronic states in luminescent systems remains a challenge in the development of fluorescent and phosphorescent dyes. Now, scientists in Japan have developed a unique organic fluorophore that changes its emission color without loss of efficiency when externally stimulated. The study published in the journal Angewandte Chemie explains this behavior by a simple phase transformation of the solid substance, which could be relevant for optoelectronic applications such as in smart OLEDs.