1448895-06-4Relevant academic research and scientific papers
Syntheses of donor-acceptor-functionalized dihydroazulenes
Broman, Soren Lindbaek,Jevric, Martyn,Bond, Andrew D.,Nielsen, Mogens Brondsted
, p. 41 - 64 (2014/01/17)
The dihydroazulene (DHA)/vinylheptafulvene (VHF) photo/thermoswitch has been of interest for use in molecular electronics and advanced materials. The switching between the two isomers has previously been found to depend strongly on the presence of donor a
Linear free-energy correlations for the vinylheptafulvene ring closure: A probe for Hammett σ values
Broman, Soren Lindbaek,Jevric, Martyn,Nielsen, Mogens Brondsted
supporting information, p. 9542 - 9548 (2013/07/26)
Linear free-energy relationships, like Hammett correlations, are fundamental in physical organic chemistry for the elucidation of reaction mechanisms. In this work, we show that Hammett correlations exist for the ring closure of six different model systems of vinylheptafulvenes (VHFs) to their corresponding dihydroazulenes (DHAs). These first-order reactions were easily followed by UV/Vis absorption spectroscopy on account of the significantly different absorption characteristics between VHFs and DHAs. Opposing effects displayed by substituent groups at two different positions are conveniently accounted for by simply subtracting the two Hammett σ values of each group. The linear correlations readily allow us to obtain unknown and approximate Hammett σ values for previously uninvestigated substituents. We also show that they can provide alternative values to the standard ones. We present values for a variety of substituent groups ranging from alkynes, sulfones, sulfoxides, and different heteroaromatics. The electronic effects exerted by substituent groups on VHFs are also reflected in their absorption maxima. Thus, we have established an empirical relationship between the absorption maximum of the VHF and the Hammett σ values of its substituents. This fine-tuning of electronic properties is particularly important for the ongoing efforts of using the DHA/VHF molecular switch in molecular electronics devices. The value of Hammett: The rate of vinylheptafulvene (VHF) ring closure to a dihydroazulene (DHA) obeys the Hammett correlation: electron-donating groups in the seven-membered ring enhance the ring closure, whereas such groups at the dicyanoethylene unit retard it (see figure). When substituents are present at both these positions, a Hammett correlation is obtained based on the difference in Hammett substituent values. Copyright
