Light emitter

The fluorescence color converter technique [32] can, in principle, overcome much of this power loss by replacing the white light emitter with a blue-emitting organic stack, and the absorbing filters with green and red fluorescent dyes. Thus when a green pixel is desired, the OLED underneath is turned on and the blui... 

In a few cases chlorophyll catabolites which had undergone ring cleavage between positions 20 and 1 were isolated as naturally occurring light-emitter substances from dinoflagcllates.47... 

Because luciferyl adenylate emitted a red chemiluminescence in the presence of base, coinciding with the red fluorescence of 5,5-dimethyloxylucferin, the keto-form monoanion Cl in its excited state is considered to be the emitter of the red light. Thus, the emitter of the yellow-green light is probably the enol-form dianion C2 in its excited state, provided that the enolization takes place within the life-time of the excited state. Although the evidence had not been conclusive, especially on the chemical structures of the light emitters that emit two different colors, the mechanism shown in Fig. 1.12 was widely believed and cited until about 1990. 

According to Branchini et al. (2004), luciferase modulates the emission color by controlling the resonance-based charge delocalization of the anionic keto-form of oxyluciferin in the excited state. They proposed the structure C5 as the yellow-green light emitter, and the structure C6 as the red light emitter. 

It should be pointed out that the structure C5 (yellow-green emitter) is identical to the structure Cl that was previously assigned to the red light emitter. 

Fig. 3.3.4 Reaction mechanism of the coelenterazine bioluminescence showing two possible routes of peroxide decomposition, the dioxetanone pathway (upper route) and linear decomposition pathway (lower route). The Oplopborus bioluminescence takes place via the dioxetanone pathway. The light emitter is considered to be the amide-anion of coelenteramide (see Section 5.4).

Formation of the excited amide anion of coelenteramide as the light emitter in the luminescence reaction of coelenterazine was experimentally supported by the experiment of Hori et al. (1973a), in which 2-methyl analogue of coelenterazine was used as the model compound. The summary of their work is as follows In the presence of oxygen, la and lb in DMF emitted bright blue luminescence (Amax 480 and 470 nm, respectively), and produced the reaction products Ha and lib, respectively. The fluorescence emission of lib (Amax 470 nm) and that of the spent chemiluminescence reaction of lb, both in DMF plus a base (potassium r-butoxide), were identical to the chemiluminescence emission of lb in DMF. The fluorescence emission of Ha... 

The rate of protonation may vary according to the structure of the light-emitter and the environment around the light emitter. In the case of chemiluminescence reactions in solutions, the hydrophobicity, permittivity (dielectric constant) and protogenic nature of the solvent are important environmental factors. In the case of bioluminescence involving a luciferase or photoprotein, the protein environment surrounding the light-emitter will be a crucial factor. 

The light emitter in Latia luminescence. The purple protein is strongly fluorescent in red. Thus, at first glance, it would appear to be a most probable candidate for the light emitter or its precursor. However, this possibility was ruled out when we found that there is no way to relate the fluorescence of the purple protein to the bioluminescence spectrum. Thus, the luciferase must contain a chromophore that produces the light emitter. 

Fig. 8.9 Possible mechanisms of the bioluminescence reaction of dinoflagellate luciferin, based on the results of the model study (Stojanovic and Kishi, 1994b Stojanovic, 1995). The luciferin might react with molecular oxygen to form the luciferin radical cation and superoxide radical anion (A), and the latter deproto-nates the radical cation at C.132 to form (B). The collapse of the radical pair might yield the excited state of the peroxide (C). Alternatively, luciferin might be directly oxygenated to give C, and C rearranges to give the excited state of the hydrate (D) by the CIEEL mechanism. Both C and D can be the light emitter.

In bioluminescence and chemiluminescence reactions, light is emitted when the energy level of light emitter molecules falls from the excited state to the ground state. The quantum yield Q of the substance A is given by ... 

Goto, T., Iio, H., Inoue, S., and Kakoi, H. (1974). Squid luminescence I. Structure of Watasenia oxyluciferin, a possible light-emitter in the bioluminescence of Watasenia scintillans. Tetrahedron Lett., pp. 2321-2324. 

Hirano, T., etal. (1993). Structure elucidation of the light emitter in aequorin bioluminescence. Tennen Yuki Kagobutsu Toronkai Koen Yoshishu 35 551-558. 

Imai, Y., et al. (2001). Fluorescence properties of phenolate anions of coe-lenteramide analogues the light-emitter structure in aequorin bioluminescence. J. Photocbem. Photobiol., A Chemistry 146 95-107. 

Isobe, M., Uyakul, D., and Goto, T. (1987). Lampteromyces bioluminescence. I. Identification of riboflavin as the light emitter in mushroom Lampteromyces japonicus. J. Biolumin. Chemilumin. 1 181-188. 

Kuse, M., et al. (2001). 7,8-Dihydropterin-6-carboxylic acid as light emitter of luminous millipede, Luminodesmus sequoiae. Bioorg. Med. Chem. Lett. 11 1037-1040. 

Shimomura, O., and Johnson, F. FI. (1973c). Chemical nature of light emitter in bioluminescence of aequorin. Tetrahedron Lett., pp. 2963-2966. 

Shimomura, O., and Teranishi, K. (2000). Light-emitters involved in the luminescence of coelenterazine. Luminescence 15 51-58. 

---