Evidence for Two Forms, Double Hydrogen Tunneling, and Proximity of Excited States in Bridge-Substituted Porphycenes: Supersonic Jet Studies

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• 作者：Alexander Vdovin ; Jerzy Sepio//pubs.acs.org/images/entities/lstrok.gif" border="0"> ; Natalia Urba//pubs.acs.org/images/entities/nacute.gif" border="0">ska ; Marek Pietrasz
• 刊名：Journal of the American Chemical Society
• 出版年：2006
• 出版时间：March 1, 2006
• 年：2006
• 卷：128
• 期：8
• 页码：2577 - 2586
• 全文大小：164K
• 年卷期：v.128,no.8(March 1, 2006)
• ISSN：1520-5126

文摘

Laser-induced fluorescence and dispersed fluorescence spectra measured in supersonic jetsfor 9,10,19,20-tetra-n-methylporphycene and 9,10,19,20-tetra-n-propylporphycene reveal, for both compounds, the presence of two different species which are assigned to trans and cis tautomeric forms. Doubletsplitting of lines is observed, disappearing upon deuteration of the inner nitrogen atoms. This finding isinterpreted as an indication of double hydrogen tunneling. The values of tunneling splitting are obtained forboth ground and lowest singlet excited states. The splitting is similar for cis and trans forms, and the barrierfor tautomerization is larger in the excited state. Due to the coupling of hydrogen motion with rotation ofalkyl substituents, tautomerization occurs in an asymmetric double minimum potential, with the ordering ofenergy minima reversed upon excitation. The second singlet excited state is found to lie very close to S₁,thus facilitating an efficient radiationless depopulation.