10.1021/jp3095787.s004
Françisco M. Raymo
Computational Insights
on the Isomerization of Photochromic
Oxazines
2012
American Chemical Society
photochromic
MPW 1PW calculations
compound
M 062X calculations
triplet
opening
relaxation
oxazine ring
isomer
oxazine ring dictates
ground state
surface
B 3LYP calculations
member
excitation
photoinduced
data
isomerization
spectra
model
2012-12-06 00:00:00
article
https://acs.figshare.com/articles/Computational_Insights_on_the_Isomerization_of_Photochromic_Oxazines/2463319
We investigated the isomerization of the simplest member
of a family
of photochromic oxazines with the aid of density functional theory,
using three different functionals. Specifically, we simulated the
thermal interconversion of the two enantiomers, associated with this
compound, and established that the opening of the oxazine ring dictates
the rate of the overall degenerate process. The M062X functional provides
the best match to experimental data, whereas B3LYP calculations fail
to model accurately the ground-state potential-energy surface of this
system. In addition, we also modeled the absorption spectra of this
compound and its photogenerated isomer with time-dependent calculations.
The resulting data support the original assignment of the experimental
spectra and confirm that the oxazine ring opens upon excitation. The
MPW1PW91 functional provides the best match to experimental data,
whereas M062X calculations fail to model accurately the spectroscopic
parameters of this particular system. Furthermore, the MPW1PW91 calculations
demonstrate that the photoinduced opening of the oxazine ring occurs
along the potential-energy surface of the first triplet excited state.
Indeed, the photoinduced isomerization appears to involve: (1) the
initial excitation of one isomer to the second singlet excited state,
(2) its thermal relaxation to the first triplet excited state, (3)
its ring opening to produce the other isomer, and (4) the thermal
relaxation of the product to the ground state. Thus, our calculations
provide valuable information on the elementary steps governing the
isomerization of this particular photochromic compound in the ground
state and upon excitation. These useful mechanistic insights can guide
the design of novel members of this family of photoresponsive compounds
with specific properties.