Simple aggregations of phosphorus-containing compounds have been investigated for the first time. The aggregators studied are O-alkyl O-4-nitrophenyl methylphosphonates (1-n and 2), 4-nitrophenyl alkylphenylphosphinates (3-n), and O-n-octyl O-4-nitrophenyl phenylphosphonate (4). Their aggregating tendencies have been evaluated by measuring their critical aggregate concentrations (CAgC's) in dioxane−H2O binary mixtures of graded compositions. Structural effects on aggregating tendencies have been discussed.
Aggregation of some sulfur-containing compounds has been studied. The aggregators studied are p-nitrophenyl esters of butylsulfonate (S-4), octylsulfonate (S-8), dodecylsulfonate (S-12), and hexadecylsulfonate (S-16). Their aggregating tendencies have been evaluated by measuring their critical aggregate concentrations (CAgCs) in dioxane−H2O binary mixtures of graded compositions. Our results indicate that the sulfonates, just like the carboxylates or phosphonates, can also be used as kinetic probes for evaluating CAgC values. If the above-mentioned three types of compounds bearing the same number of methylene groups in their chains are compared, then the order of increasing aggregating tendency appears to be phosphonate < sulfonate and carboxylate.
Electron-transfer fluorescence quenching processes in coaggre-gates between excited N-alkylcarbazoles as electron donors and 2,4-dinitrophenyl carboxylates or pentafluorophenyl carboxylates as acceptors Hydrophobic-lipophilic interaction ( HLI) , together with other foxes, can lead to the foxmation of agregatea ( Ag ' s ) , miceUes, and living cells from organic molecules in solvents with solvent aggregating power ( SW) . ' ~g ' s of electrically neutraI organic moleculeS are f o d almost solely by HLI . Molecular assemblies such as aggregates, vesicles, and mimlles are b e i i explored as artificial model systems for photophysical and photochemical studies. ' ' It has been reported that aggregation, ooaggregation, and self-coiling of organic molecules may facilitate excimer fomation energy transfer, lo or elec,tron transfer. 1 Photoinitiated electron transfer and related phenomena play an important role in life processes such as metabolism, photosynthesis, etc . , thus many researchers have looked for ways to study the basic chemistry of these processes in simplified model systems. It is well known that the eftecta of medium, polarity, sluface charge ofthe micelle,"and nature ofthe head gmup of the s u r i a~t a n , '~' *~~ as welt as chain-length of the *I group, 13a*15 all have important intluences on the behavior of photoinduced electron &er between the donor and the acceptor in solution. On the basis of our previous studies of hydrophobic acceleration of electron-transfer processes between carbon-containing compounds and pnitmphenyl carb~xylates,"*~~ we have now extended our research to those between nitrogen-containing hetemcyclic donors and fluorine-containing acceptors.In the present study, N-alkylcarbazoles ( 1-n ) with different chain-lengths ( n = 4, 8 , 12, 16) were used as the electron donor and fluorescence probe, and 2,4-dinitrophenyl carboxylates (2n ) or pentafluomphenyl carboxylates (3-12) as the acceptor and quencher.We report some novel results of electron-transfer fluorescence quenching facilitated by HLI between excited I-n and 2-n or 3-n in DX-bO system at low concentrations (-1a6M).There are three possible pathways leading to the fluorescence quenching of the excited-state fluorescence probe , namely, photoinitiated electron transfer, singletsinglet energy transfer, and triplet-triplet energy trans-F in (donodrs) 2n (acceptors) n = 4, 8, 12, 16 n = 4, a, 12, 16 3n (acceptors) n = 4, a, 12, 16 Experimental column chromatography was performed on silica gel with petroleum ether-ethyl acetate as the eluent. Reagents and the prepwatwn ofthe target compoundr Appuratw 'H NMR spectra were obtained at 90 MHz on a Varian FX-9OQ spectrometer with TMS as the internal standard and. I9F NMR on a Varian EM
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