Molecular Beam Studies on the Photodissociation Dynamicsof Aromatics and Biomolecules

• Main Authors: Chien-Ming Tseng, 曾建銘
• Other Authors: Yuan T. Lee
• Format: Others
• Language: en_US
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/11183719983930581762

博士 === 國立臺灣大學 === 化學研究所 === 96 === The photodissociation dynamics of aromatics and biomolecules have been investigated by multimass ion imaging technique. The photoisomerization and photodissociation mechanisms of aniline, 4-methylpyridine and phenol were studied. Various dissociation channels including the ground state dissociation with or without exit barrier and excited state dissociation along with N-H/O-H bond distance were observed. The “seven membered ring isomerization” of these aromatic molecules was discussed and compared with toluene. These series of studies established the basic understanding of aromatic molecules under UV irradiation. The suggestion of the deactivation from the optical bright state (π π* state) to the dark state ( repulsive πσ* state) through conical intersection has been made to explain the ultrafast decay pathway to dissipate the absorbed UV photon energy of aromatic and biomolecules. The results are the H-atom transfer (proton-electron concerted transfer) on the excited state or internal conversion to the ground state. The detail studies of photodissociation dynamics of phenol and 1-napthol was performed to test the idea in these chemical systems. By extending the research to biomolecules, the chromophores of amino acid tyrosine and tryptophan were studied. The p-methylphenol, p-ethylphenol, phenylethylamine and p-(2-aminoethyl)phenol reveal the affects of “floppy” side chain and different functional groups (e.g., amino and hydroxyl groups) on the photodissociation dynamics of these chromophores. Likewise, the studies of indole, 3-methyl-indole, tryptoamine and tryptophan are also the way to go deep into the photochemistry issue of amino acid gradually. The photodissociation dynamics of L-tryptophan in a molecular beam and its relevance to the origin of life on earth will be briefly discussed. The photodissociation of N-methyl-pyrrole, anisole and N-methylindole is the another illustration of the non-hydride heteroaromatic molecules with N-CH3/O-CH3 πσ* state. 7-azaindole, 2-aminopyridine and 8-Hydroxyquinoline were studied to clarify the repulsive N-H/O-H πσ* state which opens up a new aspect to describe the excited-state photophysics of DNA model compounds.