Hannover 2010 – scientific programme
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MO: Fachverband Molekülphysik
MO 1: Electronic spectroscopy I
MO 1.4: Talk
Monday, March 8, 2010, 15:00–15:15, F 102
Electronic spectra of 9H-substituted adenine: inductive and mesomeric effects cause a different geometry in the excited state — •Gernot Engler1, Kai Seefeld1, Oliver Grotkopp2, Jörg Tatchen3, Thomas J. J. Müller2, and Karl Kleinermanns1 — 1Institute for physical chemistry, Heinrich-Heine-University, Düsseldorf, Germany — 2Institute for organic chemistry, Heinrich-Heine-University, Düsseldorf, Germany — 3Institute for theoretical chemistry, Heinrich-Heine-University, Düsseldorf, Germany
We investigated the adenine derivatives methyl-, ethyl, butyl- and acetyladenine substituted at the 9H-position by expansion of the laser desorbed molecules in a supersonic jet following by UV excitation (REMPI). The spectra of the alkyl substituted adenines break off after a few 100 cm−1 while the acetyladenine spectrum extends up to 1000 cm−1. Furthermore the acetyladenine spectrum shows a bathochromic shift of about 1500 cm−1 in comparison to the alkyl substituted adenine. TD-DFT/BH-LYP calculations reveal a non-planar geometry for the alkyl substituted adenine in the electronically excited Lb state similar to the geometry of 9H-adenine, but a planar structure for acetyladenine. This may be the reason for the short spectra of the alkyl derivatives, because it is known that puckering of the six membered ring of 9H-adenine causes a fast relaxation pathway to the electronic ground state [1-3]. Furtheron the calculations show interaction of the π-orbitals at the carbonyl group with the ring system. This causes an enlargement of the conjugated π-orbital system which is reflected in the red shift of the acetyladenine spectrum.
C. M. Marian, J. Chem. Phys., 2005, 122, 104314
[2] L. Serrano-Andrés, M. Merchán, A. C. Borin, J. Am. Chem. Soc., 2008,
130 (8), 2473
[3] E. Fabiano, W. Thiel, J. Phys. Chem. A, 2008, 112 (30), 6859