Thermochemically induced luminescence is generated in a fluorescent labeled organic compound containing a covalently bonded fluorescent label which is a polycyclic aromatic radical having at least three linearly fused benzene rings and capable of being excited to a fluorescent electronic excited state by energy transfer from an energy donor molecule or radical having an electronic excited state, by a process comprising generating an energy donor radical or molecule by a thermochemical reaction in the presence of the fluorescent label. The energy donor radical may be generated by a chemical reaction in the presence of the fluorescent labeled organic compound or the fluorescent labeled compound itself may be additionally labeled with a radica...