Three types of “Cool Light” • Fluorescence:higher energy radiation is absorbed by a species and stored • Phosphorescence:light is absorbed by a molecule which becomes excited to a higher singlet state. • Chemiluminescence:the energy required to emit light comes from the energetics of the chemical reaction.
Chemiluminescence • The non-thermal production of visible light by a chemical reaction. • Occurs when an energy releasing reaction produces a molecule in an electronically excited state, as that molecule returns to the ground state it releases its energy as a photon of light. • Rigid and Aromatic molecules
Glow Stick • Shows temperature dependence of chemical reaction involving chemiluminescence • Energy transfer between an intermediate formed in the reaction between phenyl oxalate ester and hydrogen peroxide
Excited State • The wavelength of light emitted by a molecule is related to the energy of its excited state. E=hc/λ h= Plank’s constant λ= wavelength of emitted light(m) c= speed of light E= energy difference between emissive excited state and ground state
Bioluminescence • The production of chemiluminescence by living organisms
Direct Chemiluminescence A*→ A + light • When the emissive excited state molecules are produced directly by the reaction mechanism
Sensitized Chemiluminescence A* + B → A + B* • When an acceptor molecule receives excitation energy from an excited state species, and releases the energy as a photon of light.
Applications • Latent fingerprints • Blood/fluid tests • Entertainment • DNA testing • Spectroscopy • Pharmaceutical Industry (analysis and quality control)
Oxidation of luminol 1st report of chemiluminescence from luminol was made by Albrecht in 1928
References • http://agrippina.bcs.deakin.edu.au/bcs_courses/forensic/Chemical%20Detective/index.htm • http://www.shsu.edu/%7Echm_tgc/JPPdir/JPP1999/ • http://www.shsu.edu/~chm_tgc/chemilumdir/chemiluminescence2.html • J. Org. Chem., Vol. 35, No. 7, 1970 • http://dsc.discovery.com/fansites/onthecase/toolbox/tool_01.html • http://www.deakin.edu.au/forensic/Chemical%20Detective/Luminol_test.htm • Shakhashiri, Bassam; Chemical Demonstrations. Vol. 1 The University Of Wisconsin Press, 1983