Luminol-specific extrinsic lyoluminescence of X-ray irradiated sodium chloride

Cathodic Electrogenerated Chemiluminescence of Luminol at Disposable Oxide-Covered Aluminum Electrodes

“…Luminol normally exhibits a strong CL only in alkaline solutions. − , The p K a1 and p K a2 of luminol are 6.2−6.7 and 15.1, respectively. , Hence, luminol CL is efficient only when its singly deprotonated form LH - prevails. The chemiluminescence pathway is usually started by a hydrogen atom abstraction (8) or by one-electron oxidation followed by a rapid deprotonation of the formed LH • radical (9) (p K a of LH • is 7.7): 16 where, Ox • is a one-electron oxidant.…”

“…If hydrogen peroxide, peroxydisulfate, or peroxydiphosphate ions are added to the solution, strongly oxidizing hydroxyl radicals (5c), sulfate radicals (6), or phosphate radicals (7) are rapidly produced: with second-order rate constants k 6 = 1.2 × 10 10 L mol -1 s -1 and k 7 = 1.8 × 10 8 L mol -1 s -1 − However, it is of greater interest that the ECL intensity is also very high in the absence of these compounds in air-saturated solutions (Figures and ). …”

“…Our system clearly differs from that of Yoshimi et al because, in our cells, hot or hydrated electrons are capable of difficult reductions not encountered in traditional electrochemistry in aqueous solutions. First, the reduction step of L •- radical by a hydrated electron ( E ° = −2.9 V vs SHE) 8 has a −Δ G of 3.8 eV and −Δ H slightly less being energy-sufficient as to result in a deprotonated luminol molecule in its first excited singlet state, L 2- *, which emits at 450 nm …”

“…Measurements were generally made through an interference filter having a transmission maximum of 450 nm and bandwidth ∼10 nm. The interference filter was originally selected by assuming that the luminol ECL emission maximum would be at 450 nm, the CL emission peak wavelength when luminol CL is induced by dichlorine radical ions in the presence of hydrated electrons in deoxygenated alkaline solution . Later, it was discovered that an interference filter with a transmission maximum of 420 nm would have yielded ∼2-fold ECL signal.…”

“…We have recently shown, in our lyoluminescence studies, that the generation of sulfate radical, phosphate radical, hydroxyl radical, − or dichlorine radical ion 3 in aqueous luminol solutions induces strong chemiluminescence (CL) of luminol. It has been also demonstrated that sulfate , and hydroxyl radicals can be cathodically generated at pulse-polarized oxide-covered aluminum electrodes in fully aqueous solution.…”