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Riboflavin-induced Type 1 photo-oxidation of tryptophan using a high intensity 365 nm light emitting diode
摘要： The mechanism of photo-oxidation of tryptophan (Trp) sensitized by riboflavin (RF) was examined employing high concentrations of Trp and RF, with a high intensity 365 nm light emitting diode (LED) source under N2, 20% and 100% O2 atmospheres. Dimerization of Trp was a major pathway under the N2 atmosphere, though this occurred with a low yield (DφTrp = 5.9 x 10-3), probably as a result of extensive back electron transfer reactions between RF●- and Trp(H)●+. The presence of O2 decreased the extent of this back electron transfer reaction, and the extent of Trp dimerization. This difference is attributed to the formation of O2●- (generated via electron transfer from RF●- to O2) which reacts rapidly with Trp● leading to extensive consumption of the parent amino acid and formation of peroxides and multiple other oxygenated products (N-formylkynurenine, alcohols, diols) of Trp, as detected by LC-MS. Thus, it appears that the first step of the Type 1 mechanism of Trp photo-oxidation, induced by this high intensity 365 nm light source, is an electron transfer reaction between the amino acid and 3RF, with the presence of O2 modulating the subsequent reactions and the products formed, as a result of O2●- formation. These data have potential biological significance as LED systems and RF-based treatments have been proposed for the treatment of pathological myopia and keratitis.
关键词： type 1/type 2 mechanisms,dimers,LED,N-formylkynurenine,trimers,riboflavin,photo-oxidation,electron transfer,photobleaching,tryptophan,triplet excited state
更新于2025-09-23 15:21:21
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Dual nature of exciplexes: exciplex-forming properties of carbazole and fluorene hybrid trimers
摘要： Two exciplexes were detected for the first time for the known exciplex-forming system consisting of electron donating 1,3-bis-(N-carbazolyl)benzene and electron accepting 2,4,6-tris[3-(diphenyl-phosphinyl)phenyl]-1,3,5-triazine. Exploiting thermal treatment, sky-blue (high-energy) and orange (low-energy) exciplexes were observed for a solid-state mixture of the compounds under electrical excitation. Similarly, stable high-energy and low-energy exciplexes were observed for new exciplex-forming systems consisting of 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine and one of four selected carbazole and fluorene hybrid trimers as donors. The high-energy exciplexes were observed when there was a small energy barrier between the locally excited state and the high-energy exciplex state. A large energy barrier between the locally excited state and the low-energy exciplex state was the reason that the dual nature of exciplexes was not discovered yet. Emission of both exciplexes was observed in electroluminescence spectra of exciplex-interface based devices using developed exiplex-forming systems as emitters. Observed under optical and electrical excitations, the low-energy exciplexes were separated using thermal treatment of the studied exciplex-forming systems. The exciplex-forming system consisting of 2,4,6-tris[3-(diphenylphosphinyl)phenyl]-1,3,5-triazine and 3,6-di(9-carbazolyl)-9-(2-ethylhexyl)carbazole, which exhibits thermally activated delayed fluorescence, showed the best performance in organic light-emitting diodes (OLEDs) based on interface and volume exciplex emitters. The best device showed maximum external quantum and maximum current efficiencies of 18% and 54 cd A?1 respectively. Additionally, white OLEDs were fabricated exploiting sky-blue and orange emissions from a single exciplex-forming system. Our findings provide evidence of the dual nature of exciplexes and pave the way towards design of new exciplex-forming systems with high photoluminescence quantum yields and efficient exciplex-based devices.
关键词： OLEDs,fluorene,exciplexes,hybrid trimers,thermally activated delayed fluorescence,carbazole
更新于2025-09-19 17:15:36