Photooxidation of 9,10-diethoxyanthracene: mechanistic dichotomies between homogeneous solution and reverse micelle photoprocesses

Abstract

. Can. J. Chem. 68,612 (1990). We have compared the photooxidation of the title compound, DEA, by diphenyliodonium salts in homogeneous acetonitile (AN) and in heptane/AOT/water reverse micelle solutions. The reaction is efficient, which we attribute to rapid (ca. 10 ps) deethylation of the DEA radical cation, initially formed by photoinduced electron transfer. In AN, the electron transfer occurs from singlet excited DEA, but in reverse micelles it is gated by intersystem crossing to triplet DEA. Under these conditions, DEA fluorescence quenching by the iodonium cation may still be observed; we infer operation of the external heavy atom effect as the primary mechanism.Key words: anthracene, electron transfer, reverse rnicelle, photochemistry, picosecond.

Activation of the sol–gel process by visible light-emitting diodes (LEDs) for the synthesis of inorganic films

“…We postulate that the formation rate of H + PF 6 À superacids and its final concentration are the major parameters controlling the sol-gel process efficiency. 16,17 A slow and limited photogeneration of acid is fully consistent with the partial hydrolysis of the SiOCH 3 functions and the limited Si-O-Si network detected using RT-FTIR spectroscopy. The decrease of its maximum absorption at 520 nm (basic form), in a region sufficiently distinct from the PS absorption range, serves to monitor the extent of photoacids generated upon UV irradiation.…”

“…9 However, most aforementioned PAGs only exhibit absorption bands confined to the short wavelength region of the UV spectrum (o300 nm), without overlapping with the LED emission spectrum spanning 380-420 nm. In cationic photopolymerization of epoxy or vinyl ether monomers, an absorption shift towards the visible range has been achieved thanks to additional long-wavelength photosensitizers (PSs), such as thioxanthone derivatives, [11][12][13] electron-rich polynuclear aromatic compounds [14][15][16][17][18] and curcumin. In cationic photopolymerization of epoxy or vinyl ether monomers, an absorption shift towards the visible range has been achieved thanks to additional long-wavelength photosensitizers (PSs), such as thioxanthone derivatives, [11][12][13] electron-rich polynuclear aromatic compounds [14][15][16][17][18] and curcumin.…”

“…In cationic photopolymerization of epoxy or vinyl ether monomers, an absorption shift towards the visible range has been achieved thanks to additional long-wavelength photosensitizers (PSs), such as thioxanthone derivatives, [11][12][13] electron-rich polynuclear aromatic compounds [14][15][16][17][18] and curcumin. [10][11][12][13][14][15][16][17][18][19] In most cases, protonic acids (H + X À ) recognized as the main initiating species are released by the interaction of PS + with hydrogen donors (DH) or other photolytic radical species. This well-known mechanism proceeds by electron transfer photosensitization, as described in Scheme 1.…”

“…19 These conventional PSs with different absorption and photophysical properties allowed the efficient decomposition of PAGs upon irradiation around their maximum absorption wavelength (l max ). [11][12][13][14][15][16][17][18] The yield and generation kinetics of photoacids are greatly affected by the light absorption capability of the employed PS, deactivation of the excited 1,3 PS* such as the quantum yield of fluorescence (f f ) and phosphorescence (f p ), 10,11 driving force of electron transfer (ÀDG et ) [11][12][13][14][15][16][17][18] and the rate constants of forward and back electron transfer (BET), 12,13,16,17 and so on. PSs are responsible for absorbing light energy and generating the excited species in the singlet or triplet state 1,3 PS*.…”

“…10 In order to match the spectral emission of visible LEDs, these photoinitiating systems need modification. In cationic photopolymerization of epoxy or vinyl ether monomers, an absorption shift towards the visible range has been achieved thanks to additional long-wavelength photosensitizers (PSs), such as thioxanthone derivatives, [11][12][13] electron-rich polynuclear aromatic compounds [14][15][16][17][18] and curcumin. 19 These conventional PSs with different absorption and photophysical properties allowed the efficient decomposition of PAGs upon irradiation around their maximum absorption wavelength (l max ).…”