title: On the mechanism of intramolecular sensitization of photocleavage of the 2-(2-nitrophenyl)propoxycarbonyl (NPPOC) protecting group.
abstract: A spectroscopic study of a variety of covalently linked thioxanthone(TX)-linker-2-(2-nitrophenyl)propoxycarbonyl(NPPOC)-substrate conjugates is presented. Herein, the TX chromophore functions as an intramolecular sensitizer to the NPPOC moiety, a photolabile protecting group used in photolithographic DNA chip synthesis. The rate of electronic energy transfer between TX and NPPOC was quantified by means of stationary fluorescence as well as nanosecond and femtosecond time-resolved laser spectroscopy. A dual mechanism of triplet-triplet energy transfer has been observed comprising a slower mechanism involving the T1(pipi*) state of TX with linker-length-dependent time constants longer than 20 ns and a fast mechanism with linker-length-dependent time constants shorter than 3 ns. Evidence is provided that the latter mechanism is due to energy transfer from the T2(npi*) state which is in fast equilibrium with the fluorescent S1(pipi*) state. In the case of direct linkage between the aromatic rings of TX and NPPOC, the spectroscopic properties are indicative of one united chromophore which, however, still shows the typical NPPOC cleavage reaction triggered by intramolecular hydrogen atom transfer to the nitro group.
authors: Contribution from the Fachbereich Chemie, Universität Konstanz, 78465 Konstanz, Germany.
authors: Dominik
authors: D
authors: Wöll
authors: Stefan
authors: S
authors: Laimgruber
authors: Marina
authors: M
authors: Galetskaya
authors: Julia
authors: J
authors: Smirnova
authors: Wolfgang
authors: W
authors: Pfleiderer
authors: Björn
authors: B
authors: Heinz
authors: Peter
authors: P
authors: Gilch
authors: Ulrich E
authors: UE
authors: Steiner
mesh_terms: D002264:Carboxylic Acids / Q000737:chemistry*; D004735:Energy Transfer; D004952:Esters / Q000737:chemistry; D007700:Kinetics; D009578:Nitrobenzenes / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D010782:Photolysis; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D013892:Thioxanthenes / Q000737:chemistry; D013936:Thymidine / Q000031:analogs & derivatives / Q000737:chemistry; D044004:Xanthones / Q000737:chemistry*
chemical_list: C430114:2-nitrophenylpropyloxycarbonyl chloride; D002264:Carboxylic Acids; D004952:Esters; D009578:Nitrobenzenes; D013892:Thioxanthenes; D044004:Xanthones; C484911:thioxanthone; D010100:Oxygen; D013936:Thymidine