Spiropyrans and spirooxazines 6. the spectral and kinetic properties of 5-(4,5-diphenyl-1,3-oxazol-2-yl)-substituted spironaphthopyrans: An experimental and theoretical study

Article abstract of DOI:10.1007/s11172-011-0072-4

The spectral and kinetic properties of 5-(4,5-diphenyl-1,3-oxazol-2-yl) spiro[indoline-naphthopyran] derivatives were studied by experimental and theoretical methods. The additional long-wavelength maximum in the absorption spectra of compounds studied is due to the introduction of a diphenyloxazole fragment and corresponds to a π-π*electronic transition with a partial charge transfer character. Substituents have little effect on the kinetic parameters of the spironaphthopyrans studied.

Full text of DOI:10.1007/s11172-011-0072-4

Russian Chemical Bulletin, International Edition, Vol. 60, No. 3, pp. 456—464, March, 2011
456
Spiropyrans and spirooxazines
6. The spectral and kinetic properties of
5ꢀ(4,5ꢀdiphenylꢀ1,3ꢀoxazolꢀ2ꢀyl)ꢀsubstituted spironaphthopyrans:
an experimental and theoretical study
A. V. Chernyshev,a I. V. Dorogan,a N. A. Voloshin,b A. V. Metelitsa,a and V. I. Minkina
aInstitute of Physical and Organic Chemistry, Southern Federal University,
194/2 prosp. Stachki, 344090 Rostov on Don, Russian Federation.
Eꢀmail: anatoly@ipoc.rsu.ru
bSouthern Research Center of the Russian Academy of Sciences,
41 ul. Chekhova, 344006 Rostov on Don, Russian Federation
Fax: +7 (863 2) 43 4667. Eꢀmail: photo@ipoc.rsu.ru
The spectral and kinetic properties of 5ꢀ(4,5ꢀdiphenylꢀ1,3ꢀoxazolꢀ2ꢀyl)spiro[indolineꢀnaphꢀ
thopyran] derivatives were studied by experimental and theoretical methods. The additional
longꢀwavelength maximum in the absorption spectra of compounds studied is due to the introꢀ
duction of a diphenyloxazole fragment and corresponds to a π—π* electronic transition with
a partial charge transfer character. Substituents have little effect on the kinetic parameters of
the spironaphthopyrans studied.
Key words: spiropyrans, photochromism, quantum chemical calculations, density funcꢀ
tional theory, timeꢀdependent density functional theory, PBE0 and B3LYP functionals.
Scheme 1
The synthesis and investigations of new photochromic
compounds to design polyfunctional materials for molecꢀ
ular electronics and chemical sensors is a key problem in
modern chemistry. Among wellꢀknown classes of photoꢀ
chromic compounds, spiropyrans occupy a special posiꢀ
tion because they can vary their spectral and kinetic propꢀ
erties in a rather wide range depending on the molecular
structure and can fairly easily be synthesized.2—4
Photochromic transformations of spironaphthopyrans
(SNPs) (Scheme 1) are due to thermally and photochemꢀ
ically reversible heterolytic dissociation of the CSp—O
bond in the cyclic isomer A followed by cis—transꢀisomerꢀ
ization to the metastable merocyanine form B.2,3
By introducing various functional fragments into spiroꢀ
pyran molecules one can obtain polyfunctional molecular
systems that exhibit not only photochromic, but also phoꢀ
toswitchable magnetic,5 complexꢀforming,6—9 and fluoꢀ
rescence9—12 properties. Earlier,13 we have reported the
synthesis of a photochromic 5ꢀ(4,5ꢀdiphenylꢀ1,3ꢀoxazolꢀ
2ꢀyl)substituted spiro[indolineꢀnaphthopyran] whose meroꢀ
cyanine form is involved in reversible complexation with
divalent heavy metal cations owing to participation of doꢀ
nor atoms of the 4,5ꢀdiphenylꢀ1,3ꢀoxazole fragment in
ion coordination. It was established that this fragment in
the SNP structure is responsible for the appearance of an
R1 = H (1, 2), Cl (3), OMe (4)
R2 = H (1),
(2—4)
additional longꢀwavelength band in the absorption specꢀ
trum. However, no detailed studies to elucidate the nature
of electronic transitions determining the spectral properꢀ
ties of such compounds were carried out. In addition, it is
For Part 5, see Ref. 1.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 447—454, March, 2011.
1066ꢀ5285/11/6003ꢀ456 © 2011 Springer Science+Business Media, Inc.

5ꢀDiphenyloxazolyl spironaphthopyrans
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
457
TD PBE0/6ꢀ311G* and TD B3LYP/6ꢀ311G*//PBE0/6ꢀ311G*
methods.
The energies of the first singlet electronic transitions of meroꢀ
cyanines were corrected using a linear dependence17
interesting to investigate how the additional substituent in
the indoline fragment of the molecule influences the specꢀ
tral and kinetic properties of SNPs.
Experimental
ΔEcorr = –0.0963 + 0.9321ΔEcalc
,
where ΔEcalc is the energy of the first singlet transition of meroꢀ
cyanine obtained from TD B3LYP/6ꢀ311G* calculations for
a solution in ethanol (ε = 24.55). Making use of this correlation
in the TD B3LYP/6ꢀ311G*//PBE0/6ꢀ311G* calculations for
a solution in acetone seems to be quite correct because the diꢀ
electric constants of acetone and ethanol are close and the geoꢀ
metric parameters of the systems in question computed using the
PBE0 and B3LYP functionals18—20 and the same basis set differ
insignificantly.
Compounds 1—4 were synthesized according to the known
procedures.13,14 Solutions were prepared using toluene and aceꢀ
tone (Aldrich, both of "spectroscopic" grade) as solvents.
Electronic absorption spectra and the kinetics of thermal
recyclization of compounds 1—4 were recorded on an Agilent
8453 spectrophotometer equipped with a thermostatting accesꢀ
sory. Solutions were irradiated with a filtered light from a highꢀ
pressure mercury lamp on a Newport 66902 equipment. Monoꢀ
chromatic radiation was cut with interference filters (λ = 365 nm).
The optical radiation power was measured by a Newport Power
Meter 2903ꢀC photoreceiver.
All calculations were carried out using the GAUSSIANꢀ03
program.21
Results and Discussion
Calculation Procedure
Spectral properties. In the solutions in toluene and
acetone, the proportion of the cyclic SNP isomers A (see
Scheme 1) is almost 100%, as indicated by the lack of
noticeable absorption in the visible region characteristic
of the acyclic merocyanine structures B.2,3 The cyclic form
1 in toluene is characterized by a structured absorption
band with maxima at 348 and 361 nm (ε = 4710 and
4360 L mol–1 cm–1, respectively). The absorption bands
of 5ꢀdiphenyloxazoleꢀsubstituted compounds 2—4 have
maxima at about 340 nm; however, the heterocyclic subꢀ
stituents cause the appearance of an additional longꢀwaveꢀ
length band in the region 370—400 nm (Table 1). On
going from toluene to acetone, the absorption bands unꢀ
Geometry optimization for the systems corresponding to the
stationary points on the groundꢀstate potential energy surfaces
(PESs) of the systems under study was performed within the
framework of the density functional theory (DFT) using the
PBE0 hybrid functional15 and the 6ꢀ311G* basis set. The search
for transition states was done by the synchronous transit method
(QST3). The nature of the stationary points was determined
based on the results of vibrational frequency calculations (force
constant matrix). The solvent effect was included within the
framework of the CPCM model.16 The dielectric constant of the
medium was set equal to that of acetone (ε = 20.7).
The optimized geometric parameters of the structures correꢀ
sponding to minima on the PES were used in the timeꢀdepenꢀ
dent DFT calculations of absorption spectra in acetone by the
Table 1. Spectral properties of SNPs 1—4* in solutions in toluene and acetone
SNP Isomer
Toluene
Acetone
abs
max
ex flu
flu
max
ex ph
ph
max
abs
max
ex flu
flu
λ
max
λ
(λ
)
λ
(λ
)
λ
λ
(λ )
max
max
max
(ε•103/L mol–1 cm–1
)
(ε•103/L mol–1 cm–1
)
1
2
3
4
A
300 (9.52), 313 (7.79),
348 (4.71), 361 (4.36)
562
304 (25.62), 342 (19.66),
380** (8.30), 395** (5.90)
596
—
—
—
—
—
346 (4.20), 359 (4.00)
—
—
B
A
558
600
—
396
562
560 600
380 410
398, 404 420, 432**
574, 625, 338 (19.10), 375 (6.30),
680**
—
392 (4.60)
588
B
A
590 618
—
580 620
306 (30.67), 342 (23.13),
380 (8.63), 396 (6.12)
385, 393 410, 430, 385, 393 580, 630, 337 (21.90), 380 (6.38), 381, 426
450**
685**
—
400 (3.84)
595
400
590 625
B
A
—
309 (33.70), 341 (24.40),
380 (9.40), 397 (6.50)
385, 400 410**, 430, 370, 400 577, 630, 334 (21.28), 378** (6.77), 398, 432,
465
690
—
394 (5.02)
602
408 463**
590 630
B
—
ex
ex ph
* Absorption at 293 K, luminescence at 77 K (glassꢀforming mixture toluene—ethanol—Et2O); λ abs, (λ
)
flu, λ flu, (λ
)
max
max
max
max
and λ ph (nm) are the wavelengths of maxima in the absorption spectrum, fluorescence excitation spectrum, fluorescence spectrum,
max
phosphorescence excitation spectrum, and phosphorescence spectrum, respectively.
** Shoulder.

458
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
Chernyshev et al.
A
dergo a small hypsochromic shift. The fluorescence maxiꢀ
ma of spirocyclic isomers lie at 420—430 nm. As the soluꢀ
tion temperature decreases to 77 K, the fluorescence inꢀ
tensity considerably increases and phosphorescence charꢀ
acterized by a structured band with maxima at 580 and
630 nm appears. Unlike compounds 2A—4A, the unsubꢀ
stituted SNP 1A emits no luminescence (see Table 1).
At room temperature, the compounds under study exꢀ
hibit no photochromism. A decrease in temperature of
SNP solutions allows one to disclose their photochromic
properties, which are not observed under steadyꢀstate irraꢀ
diation at 293 K owing to high rate of the reverse thermal
recyclization B → A. UV irradiation of colorless SNP soꢀ
lutions at T < 273 K is followed by their coloration. In the
electronic absorption spectra, this is accompanied by the
appearance of longꢀwavelength absorption bands with
maxima in the region 562—602 nm (see Table 1, Fig. 1).
This absorption is characteristic of the acyclic merocyaꢀ
nine structures B.2,3
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
350 400
450
500
550
600
650 λ/nm
Fig. 1. Absorption spectra of compound 3 in acetone obtained
upon irradiation at λ = 365 nm; the spectra were acquired with
2 s intervals, C(3) = 9.5•10–5 mol L–1, T = 259 K.
The introduction of a diphenyloxazolyl substituent
(SNPs 2—4) causes a bathochromic shift of absorption
maxima of the merocyanine forms B (see Table 1) relative
to the bands in the spectrum of unsubstituted SNP 1. The
merocyanine forms B of the SNPs 1—4 emit bright fluoresꢀ
cence in the region 550—720 nm; maxima of the fluorescence
1.439
1.335
1.450
1.493
1.462
1.574
1.388
1.424
1.336
1.568
O
N
1.345
1.449
1.470
1.498
23.42
1.346
1.458
1.299
O
31.74
1.421
1.384
O
1.355
1.37N9
1.366
N
1.373
1A
C
2A
1.438
1.575
1.440
1.460
1.334
1.492
1.334
1.450
1.423
Cl
O
1.450
1.388
1.492
1.388
O
1.463
N
N
1.344
O 1.346
O
1.424
25.80
1.458
1.299
N
O1.346
1.346
1.459
O
1.366
31.05
31.91
1.299
N
1.379
1.366
1.379
1.373
1.372
3A
4A
Fig. 2. Geometric parameters of spironaphthopyrans 1A—4A in solution in acetone obtained from PBE0/6ꢀ311G* calculations. Here
and in Figs 3 and 8 shown are the bond lengths (Å) and dihedral angles (deg).

5ꢀDiphenyloxazolyl spironaphthopyrans
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
459
Table 2. Excitation energies Ecalc (eV) and oscillator strengths f
of the first four singlet transitions of the spirocyclic forms of the
spironaphthopyran derivatives 1A—4A in solution in acetone:
results of TD PBE0/6ꢀ311G** calculations and experimenꢀ
tal values
bands of the isomers 2B—4B undergo a bathochromic
shift relative to the spectrum of compound 1B (see Table 1).
To elucidate the nature of the electronic transitions
responsible for maxima in the absorption spectra of SNPs
and their open forms, we calculated the excitation enerꢀ
gies within the framework of the TD DFT approach. The
results obtained are listed in Tables 2 and 3.
SNP
Transition
TD PBE0/6ꢀ311G*
calculations
Experiꢀ
ment,
The calculated structures of the cyclic and open SNP
isomers are presented in Figs 2 and 3.
f
Ecalc
Eobs
From the results of calculations it follows that the
absorption spectra of the compounds under study strongꢀ
ly depend on the substituents in the indoline and
naphthopyran fragments. In particular, for the unsubstiꢀ
tuted SNP the strongest absorption band corresponds
to the π—π*ꢀtransition S0 → S2 (major contribution
from HOMOꢀ1 → LUMO) localized on the naphthopyrꢀ
an fragment. The first singlet transition corresponds
to a weak band (HOMO → LUMO) characterizing
charge transfer from the indoline to the naphthopyran
fragment.
The introduction of the diphenyloxazolyl substituent
into the naphthopyran fragment causes the appearance of
an additional maximum on the longꢀwavelength absorpꢀ
tion band. Strong second and third singlet transitions
(HOMOꢀ2 → LUMO and HOMOꢀ1 → LUMO, respecꢀ
1A
S0 → S1
S0 → S2
S0 → S3
S0 → S4
0.092
0.154
0.021
0.036
3.490
3.746
4.337
4.565
3.454
3.584
—
—
2A
S0 → S1
S0 → S2
S0 → S3
S0 → S4
0.018
0.125
0.483
0.020
3.333
3.364
3.486
3.890
3.163
3.307
3.669
—
3A
S0 → S1
S0 → S2
S0 → S3
S0 → S4
0.131
0.021
0.472
0.173
3.369
3.409
3.478
3.900
3.100
3.263
3.473
3.680
4A
S0 → S1
S0 → S2
S0 → S3
S0 → S4
0.004
0.130
0.485
0.006
3.029
3.366
3.500
3.567
3.147
3.280
3.473
3.713
1.392
1.472
1.400
1.384
1.456
1.301
1.356
1.234
N
1.419
1.344
1.389
1.382
1.379
2.063O
1.466
1.471
1.457
N
1.358
1.438
2.698
1.402
O
1.364
1.374
N
1.347
2.069
1.240
O
1TTC
2TTC
C
1.390
Cl
1.394
1.402
1.381
1.398
1.474
1.471
1.344
1.359
1.352
1.456
1.301
1.456
1.302
1.234
1.235
2.054
1.386
1.344
N
N
2.701O
N
1.379
O
1.379
2.701 O
N
2.697
1.374
O
1.374
3TTC
4TTC
Fig. 3. Geometric parameters of the merocyanine forms 1TTC, 2TTC, 3TTC, and 4TTC in solution in acetone obtained from
PBE0/6ꢀ311G* calculations.

460
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Chernyshev et al.
Table 3. Excitation energies Ecalc (eV) and oscillator strengths f of the first four singlet transitions of the merocyanines
1TTC—4TTC in solution in acetone calculated by the TD PBE0/6ꢀ311G** and TD B3LYP/6ꢀ311G*//PBE0/6ꢀ311G*
methods, excitation energies of the first singlet transitions obtained from TD B3LYP/6ꢀ311G*//PBE0/6ꢀ311G* calculaꢀ
tions with inclusion of linear correction Ecorr (eV), and the observed excitation energies Eobs (eV)
SNP
Transition
Calculations
Experiꢀ
ment,
TD PBE0/6ꢀ311G*
TD B3LYP/6ꢀ311G*//PBE0/6ꢀ311G*
f
Ecalc
f
Ecalc
Ecorr
Eobs
1TTC
2TTC
3TTC
4TTC
S0 → S1
S0 → S2
S0 → S3
S0 → S4
0.936
0.000
0.101
0.132
2.660
3.002
3.446
3.918
0.908
0.000
0.090
0.114
2.610
2.905
3.311
3.799
2.336
2.206
S0 → S1
S0 → S2
S0 → S3
S0 → S4
0.787
0.286
0.002
0.306
2.474
2.820
3.003
3.424
0.682
0.318
0.002
0.283
2.402
2.684
2.889
3.290
2.142
2.125
2.102
2.109
2.084
2.060
S0 → S1
S0 → S2
S0 → S3
S0 → S4
0.805
0.322
0.003
0.316
2.461
2.779
2.992
3.446
0.674
0.383
0.003
0.288
2.384
2.648
2.880
3.312
S0 → S1
S0 → S2
S0 → S3
S0 → S4
0.908
0.2432
0.003
0.268
2.425
2.827
3.014
3.349
0.836
0.238
0.002
0.256
2.359
2.684
2.898
3.210
TTC is the transꢀtransꢀcisꢀisomer.
tively) are of π—π* character with partial redistribution of
the electron density from the phenyl rings of the substituꢀ
ent to the naphthopyran fragment (Fig. 4). In this case,
the first singlet transition (HOMO → LUMO) is of the
same character as for the unsubstituted compound. In adꢀ
dition to these changes, the absorption bands of the diꢀ
phenyloxazolyl derivatives undergo a bathochromic shift
compared to the spectrum of the unsubstituted compound;
this agrees with the experimental data.
a significant decrease in the intensity of the second singlet
transition (HOMOꢀ1 → LUMO). This is due to invesrion
of the HOMO and HOMOꢀ1 states of compound 3A comꢀ
pared to the unsubstituted structure 2A. The shape of the
HOMO for 3A almost matches that of the HOMOꢀ1 for
2A. Thus, the strongest longꢀwavelength bands correspond
to the transitions S0 → S1 (HOMOꢀ2 → LUMO) and
S0 → S3 (HOMO → LUMO).
An additional electronꢀdonating substituent OMe inꢀ
troduced into the indoline fragment of molecule 4A influꢀ
ences the spectrum oppositely. By and large, the nature of
An additional electronꢀwithdrawing substituent (Cl)
in the indoline fragment of molecule 3A is responsible for
HOMOꢀ2
HOMOꢀ1
LUMO
Fig. 4. Molecular orbitals of compound 2A responsible for the transitions S0 → S2 and S0 → S3. Hereafter, the MO contours are plotted
at a level of 0.03 au.

5ꢀDiphenyloxazolyl spironaphthopyrans
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
461
HOMOꢀ1
HOMO
LUMO
Fig. 5. Molecular orbitals of compound 2B responsible for the transitions S0 → S1 and S0 → S2.
transitions remains the same as for the unsubstituted molꢀ
ecule 2A. Only a bathochromic shift of absorption maxiꢀ
ma is observed, the largest shift (by about 0.3 eV) being
observed for the absorption band corresponding to the weak
first singlet transition (HOMO → LUMO) characterizing
charge transfer from the indoline fragment to the spiroꢀ
conjugated molecular fragment.
The differences between the calculated and experimenꢀ
tally determined energies of the singlet transitions in the
SNPs under study lie in the range 0.005—0.27 eV, being
on the average at most 0.2 eV.
If for the SNPs both longꢀwavelength absorption bands
correspond to the π—π* transitions due to redistribution
of the electron density in the chromene fragment (includꢀ
ing the diphenyloxazolyl substituent), for the correspondꢀ
ing merocyanine isomers these bands are due to electronic
transitions of essentially different nature. The strongest
transition S0 → S1 (HOMO → LUMO) is of π—π* charꢀ
acter not related to the changes in the electron density on
the diphenyloxazolyl substituent, whereas the second sinꢀ
glet transition (HOMOꢀ1 → LUMO) is of clearly defined
changeꢀtransfer character. By and large, the electron denꢀ
sity is redistributed from the diphenyloxazolyl substituent
to other molecular fragments (Fig. 5).
Substituents in the indoline moieties of the merocyanꢀ
ines affect only positions of the longꢀwavelength absorpꢀ
tion maxima and do not influence the nature of the correꢀ
sponding electronic transitions. The introduction of the
electronꢀwithdrawing substituent (Cl) causes a bathochroꢀ
mic shift of these absorption bands. The electronꢀdonatꢀ
ing substituent (OMe) makes this effect more pronounced.
The calculated changes in the spectroscopic properties of
the compounds under study are in qualitative agreement
with experimental observations. An additional linear corꢀ
rection of position of the longꢀwavelength absorption maxꢀ
ima of the merocyanines significantly reduces computaꢀ
tional errors (see Table 3).
Kinetic properties. We analyzed the dependence of the
rate constants for the thermal reaction B → A on the soluꢀ
tion temperature. From the data shown in Fig. 6 it follows
that the temperature dependences of the rate constants
kBA for the thermal reactions in acetone are of the Arrheꢀ
nius type (Fig. 7). This allowed the activation energies of
the thermal bleaching reactions to be determined (Table 4).
lnkBA
ln(A/A0)
0
–0.5
–1
–2
–3
–4
4
3
2
–1.0
–1.5
1
–2.0
10
20
30
40
50
t/s
3.7
3.8
3.9
T–1•103/K–1
Fig. 6. Linear anamorphoses of the kinetic curves of thermal
bleaching of irradiated solution of SNP 3 in acetone at T = 274 (1),
266 (2), 259 (3), and 250 K (4).
Fig. 7. Logarithm of the rate constant for the reverse (B → A)
thermal reaction of SNP 3 plotted vs. temperature (with acetone
as solvent).

462
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
Chernyshev et al.
Table 4. Rate constants (T = 293 K) for, and activaꢀ
tion energies of, the reverse thermal reaction of
isomerization B → A of SNPs in acetone
ular fragment about the central C—C bond in the methine
bridge. This may result in either a kinetically unstable
cisꢀ intermediate undergoing a lowꢀbarrier transformation
to a closed form or (if the formation of such an intermediꢀ
ate is sterically hindered) the cyclic form itself. In all casꢀ
es, the kinetic properties of the reverse reaction can be
evaluated by estimating the activation barrier to the
cis—transꢀisomerization of merocyanine. The calculated
geometric parameters of the corresponding transition states
are shown in Fig. 8.
SNP
kBA/s–1
EaBA/kcal mol–1
1
2
3
4
29.019
11.144
8.147
18.9
20.9
16.6
24.9
4.143
According to calculations, for all compounds investiꢀ
gated the closed forms are thermodynamically more stable
than the corresponding merocyanine isomers. The introꢀ
duction of the diphenyloxazolyl substituent into the
naphthopyran fragment slightly destabilizes the open form.
An additional electronꢀwithdrawing substituent (Cl) in the
indoline moieties of the compounds studied enhances this
effect, whereas the electronꢀdonating substituent (OMe)
cause it to weaken (Table 5).
The mechanism of spirocyclization of the merocyanꢀ
ine forms of indoline spiropyrans was studied in detail
(see, e.g., Ref. 22). It was assumed that the initial reactant
is the thermodynamically most stable merocyanine isomer
(in this case, the transꢀtransꢀcisꢀisomer, or the TTCꢀisoꢀ
mer). Computer simulation of thermal relaxation of the
merocyanine forms of indoline spiropyrans suggested that
the limiting stage of the reaction is rotation of one molecꢀ
99.33
1.353
1.469
1.469
1.482
1.453
1.299
N
1.215
1.389
2.862O
1.353
1.343
N
1.380
98.97
1.344
1.497
23.22 O
1.469
1.342
1.531
1.375
1.363
1.221
1.391
2.846
O
N
C
1TS
2TS
100.27
1.353
Cl
1.353
1.215
98.92
1.495
1.496
1.482
1.216
1.453
1.391
1.482
1.453
1.299
N
1.387
1.469
1.469 O
1.342
1.344
N
23.75
O
N
N
1.344 1.299 1.380
22.82
1.344
1.375
O
1.363
1.380
O
1.363
1.375
3TS
4TS
Fig. 8. Geometric parameters of transition states (TS) of the reverse thermal reaction 1TS, 2TS, 3TS, and 4TS in solution in acetone
obtained from PBE0/6ꢀ311G* calculations.

5ꢀDiphenyloxazolyl spironaphthopyrans
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 3, March, 2011
463
Table 5. Total energies calculated taking account of zeroꢀpoint
vibrational energy correction Etot + ZPE (au) and the relative
energies ΔE (kcal mol–1) of the structures corresponding to the
critical points on the reaction pathways of thermal relaxation of
the merocyanine TTCꢀisomers of spironaphthopyrans 1—4, and
the open form and an increase in the activation barrier to
the reverse thermal reaction. Additional electronꢀwithꢀ
drawing substituent (Cl) in the indoline fragments of the
molecules in question causes this barrier to decrease,
whereas the electronꢀdonating substituent (OMe) leads to
its decrease.
the imaginary vibrational frequencies ν (cm–1) of the strucꢀ
im
tures of transition states (TS) in the solution in acetone obtained
from PBE0/6ꢀ311G** calculations
This work was financially supported by the Ministry of
Educaton and Science of the Russian Federation (Federal
Target Program "Scientific and Pedagogical Staff of Innoꢀ
vation Russia, Years 2009—2013", under the State Conꢀ
tract No. P2346) and the Russian Foundation for Basic
Research (Project No. 09ꢀ03ꢀ93115).
Structure
–(Etot + ZPE)
ν
ΔE
im
1A
1017.702657
1017.671032
1017.698675
1723.838754
1723.803932
1723.832228
2183.312774
2183.304650
2183.277887
1838.229602
1838.194650
1838.224420
—
i202.6
—
—
i179.1
—
—
i158.0
—
—
i205.8
—
0
1TS
1TTC
2A
2TS
2TTC
3A
3TS
3TTC
4A
4TS
4TTC
19.8
2.5
0
21.9
4.1
0
21.9
5.1
0
21.9
3.3
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in revised form December 7, 2010