Nonradiative decay route of cinnamate derivatives studied by frequency and time domain laser spectroscopy in the gas phase, matrix isolation FTIR spectroscopy and quantum chemical calculations
Ebata, Takayuki
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https://hdl.handle.net/2142/97182
Description
Title
Nonradiative decay route of cinnamate derivatives studied by frequency and time domain laser spectroscopy in the gas phase, matrix isolation FTIR spectroscopy and quantum chemical calculations
Author(s)
Ebata, Takayuki
Issue Date
2017-06-20
Keyword(s)
Multiple potential energy surfaces
Abstract
The nonraddiative dececy route involving trans $rightarrow$ cis photo-isomerization from the S$_1$ ($pi$$pi$*) state has been investigated for several trans-cinnamate derivatives, which are known as sunscreen reagents. We examined two types of substitution effects._x000d_
_x000d_
One is structural isomer such as ortho-, meta-, and para-hydroxy-methylcinnmate (o-, m-, p-HMC). The S$_1$ lifetime of p-HMC is less than 8 ps at zero-point level, and it undergoes rapid S$_1$ $rightarrow$ $^1$n$pi$* $rightarrow$ T$_1$ decay via multiple conical intersections. Finally, the trans $rightarrow$ cis isomerization proceeds in the T$_1$ state. On the other hand, both o- and m-HMC show very slow decay. Their S$_1$ lifetimes are in the order of 100 ps even at the excess energy of 2000-3000 wn. _x000d_
_x000d_
The other is the effect of the complexity of ester group in para-subsitituted species, such as para-methoxy-methyl, -ethyl and -2ethylhexyl cinnamate (p-MMC, p-MEC, p-M2EHC). p-MMC and p-MEC show sharp S$_0$ $rightarrow$ S$_1$ ($pi$$pi$*) vibronic bands, while p-M2EHC shows only broad structureless feature even under the jet-cooled condition. In addition, we found that the S$_0$ $rightarrow$ $^1$n$pi$* absorption appears at 1000 wn below the S$_0$ $rightarrow$ S$_1$ ($pi$$pi$*) transition in p-MEC and p-M2EHC, but not in p-MMC. Thus, the complexity of the ester group is very important for the appearance of the $^1$n$pi$* state.
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