title: Excited-state double proton transfer of 7-azaindole dimers in a low-temperature organic glass.
abstract: The excited-state double proton transfer of model DNA base pairs, 7-azaindole (7AI) dimers, is explored in a low-temperature organic glass of n-dodecane using picosecond time-resolved fluorescence spectroscopy. Reaction mechanisms are found to depend on the conformations of 7AI dimers at the moment of excitation; whereas planar conformers tautomerize rapidly (<10 ps), twisted conformers undergo double proton transfer to form tautomeric dimers on the time scale of 250 ps at 8 K. The proton transfer is found to consist of two orthogonal steps: precursor-configurational optimization and intrinsic proton transfer via tunneling. The rate is almost isotope independent at cryogenic temperatures because configurational optimization is the rate-determining step of the overall proton transfer. This optimization is assisted by lattice vibrations below 150 K or by librational motions above 150 K.
authors.affiliation: School of Chemistry, Seoul National University, Seoul, Korea.
authors.forename: Hyeongtaek
authors.initials: H
authors.lastname: Lim
authors.forename: Sun-Young
authors.initials: SY
authors.lastname: Park
authors.forename: Du-Jeon
authors.initials: DJ
authors.lastname: Jang
mesh_terms: D000473:Alkanes / Q000737:chemistry; D020029:Base Pairing; D003080:Cold Temperature; D019281:Dimerization; D005898:Glass; D006860:Hydrogen Bonding; D007211:Indoles / Q000737:chemistry* / Q000378:metabolism; D007536:Isomerism; D007700:Kinetics; D008027:Light; D008956:Models, Chemical; D018716:Molecular Mimicry; D055668:Photochemical Processes / Q000528:radiation effects; D011522:Protons; D013050:Spectrometry, Fluorescence
chemical_list: C023422:7-azaindole dimer; D000473:Alkanes; D007211:Indoles; D011522:Protons; C007548:n-dodecane