Spectroscopic, photochromic and kinetic behavior of photo conversion of Aberchrome 540 in an ionic liquid media

Article abstract of DOI:10.1016/j.saa.2018.06.032

The photo-bleaching reaction of the chemical actinometer, Aberchrome 540, is reported for the first time in a series of ionic liquids (ILs). This fulgide in its C-form undergoes an opening reaction to yield its E-form, when it is irradiated with UV light at wavelengths >400 nm. The magnitude of bleaching was monitored spectrophotometrically and their kinetics evaluated, obtaining first-order rate constants (k_obs). The results obtained in different ILs suggest that changes in the rate constants (k_obs) of the opening reaction of Aberchrome 540 are mainly governed by weaker interactions such as coulombic (π* parameter) and Van der Waals interactions (δ_H ², parameter). In addition, the photochemical fatigue resistance was also studied in ILs media and compared with conventional solvents (benzene, toluene, etc.). In particular, we found that three different tendencies dependent on the ILs used exist. The first group of ILs where the reversibility of the fulgide is favored (for example, [Bmim][BF₄], [Bmim][PF₆] and [Bmim][OTf]), behaviour similar to conventional solvents. The second group corresponds to ILs where photo reversibility is partial; and finally, other group of ILs that prevented photo reversibility. It is proposed that depending on the ILs used, the stabilization of different forms of the fulgide can be controlled, thus resulting important in terms of choosing the appropriate ILs for a specific photochemical reaction.

Full text of DOI:10.1016/j.saa.2018.06.032

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 204 (2018) 125–130
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular
Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectroscopic, photochromic and kinetic behavior of photo conversion of
Aberchrome 540™ in an ionic liquid media
a
a
b
a
a,
M.E. Aliaga , P. Pavez G , J.R. De la Fuente , O. Núñez , A. Cañete ⁎
a
Facultad de Química, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 6094411, Chile
Departamento de Química Orgánica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Casilla 223, Santiago 1, Chile
b
a r t i c l e i n f o
a b s t r a c t
Article history:
The photo-bleaching reaction of the chemical actinometer, Aberchrome 540™, is reported for the first time in a
series of ionic liquids (ILs). This fulgide in its C-form undergoes an opening reaction to yield its E-form, when it is
irradiated with UV light at wavelengths N400 nm. The magnitude of bleaching was monitored spectrophotomet-
rically and their kinetics evaluated, obtaining first-order rate constants (kobs). The results obtained in different ILs
Received 27 April 2018
Received in revised form 7 June 2018
Accepted 9 June 2018
Available online 15 June 2018
suggest that changes in the rate constants (kobs) of the opening reaction of Aberchrome 540™ are mainly
2
governed by weaker interactions such as coulombic (π* parameter) and Van der Waals interactions (δ
H
, param-
Keywords:
Fulgide Aberchrome 540™
Ionic liquids
eter). In addition, the photochemical fatigue resistance was also studied in ILs media and compared with conven-
tional solvents (benzene, toluene, etc.). In particular, we found that three different tendencies dependent on the
Photobleaching reaction
Photoconversion
Photochemical fatigue resistance
ILs used exist. The first group of ILs where the reversibility of the fulgide is favored (for example, [Bmim][BF
4
],
[Bmim][PF ] and [Bmim][OTf]), behaviour similar to conventional solvents. The second group corresponds to
6
ILs where photo reversibility is partial; and finally, other group of ILs that prevented photo reversibility. It is pro-
posed that depending on the ILs used, the stabilization of different forms of the fulgide can be controlled, thus
resulting important in terms of choosing the appropriate ILs for a specific photochemical reaction.
©
2018 Elsevier B.V. All rights reserved.
1
. Introduction
Aberchrome 540™. In particular the study carried out by Rappon [8] on
a number of solvents of various polarities and at different temperatures.
The authors reported that the polarity of the solvent can delay the rate
of the ring opening of the dye. However, they found that the polarity
is not the only factor affecting the rate of the photochromic reaction.
Other aspects, such as the viscosity and the ability of the solvent mole-
cules to form inter-molecular hydrogen bonds with the dye, might also
affect the rate of the reaction [8].
Chemical actinometers are compounds that can undergo photo-
chemical conversion due to the action of light which can lead to revers-
ible or irreversible chemical changes [1–3]. In 1981, Heller [4] reported
for the first time the photochromism of a fulgide containing a 2,5-di-
methyl-3-furyl moiety which had been used as a classic chemical acti-
nometer in the UV–vis range, whose commercial name is Aberchrome
5
40™.
It is known that the photochromic properties of this fulgide depend
Ionic liquids (ILs) are receiving increasing attention due to the differ-
ent kinds of ions available, adding a “designer” aspect to these com-
pounds, with the results that such liquids could provide solvents with
specifically individualized properties [9]. Therefore, ILs are very attrac-
tive solvents for studying photochromic molecules due to their distinct
properties. For instance, photochromic colorants like spiropyrans and
their derivatives are the most studied system in ILs up to now. As
such, the effect of cation-anion combination in ILs, and their physical-
chemical properties, on the photochromism of spiropyran (close form)
and the thermal reversion of its open form (zwitterionic merocyanine)
have been investigated. Interestingly, spiropyrans are able to yield re-
versible photochromism in most of the ILs studied [10]. Among all ILs in-
on the UV light-induced electrocyclic ring closure, from the colorless
open forms (namely “E-form”) to the colored form (abbreviated as the
“C-form”), [5] and by the reverse C → E ring-opening, which can be ini-
tiated by visible light. However, a photoisomerisation, which connects
the (E) and (Z) isomers [4–7] (Scheme 1) could occur as a side reaction
competing with the photocyclization thereby hindering the application
as a reversible actinometer. This E–Z isomerization raises considerable
interest in the study of which factors affect the efficiency of this light-
induced ring-close/opening reaction.
In fact, some studies have demonstrated that the polarity of the me-
dium could affect the rate of the photoreaction from C-form to E-form of
vestigated, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([Bm
2
im]
[
BF ]), despite having relatively lower polarity, exhibits the lowest ther-
4
mal reversion rate, which was ascribed to solvent relatively high viscosity
in the temperature range between 293 and 313 K. Other interesting
⁎
Corresponding author.
E-mail address: acanetem@uc.cl (A. Cañete).
https://doi.org/10.1016/j.saa.2018.06.032
386-1425/© 2018 Elsevier B.V. All rights reserved.
1

126
M.E. Aliaga et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 204 (2018) 125–130
Scheme 1. Reaction scheme of the fulgide Aberchrome 540™ [5].
studies regarding the photochromism of nitrospiropyran derivatives in a
series of imidazolium-based room-temperature ionic liquids (RTILs) con-
taining anions from organic carboxylic acids have been reported [11]. It
was found that the spiropyrans could present different photochromic
behaviors, depending mainly on the polarity properties of the RTILs and
also on their own structures. It is important to mention that other
phothocromic molecules such as Spirooxazines [12] and Diarylethenes
chloride. Water contents determined by Karl-Fisher titration were
b200 ppm for all of them before they were used. Absorption spectra
were obtained using a HP-8453 diode array spectrophotometer.
2.2. Synthesis of Aberchrome 540™
Fulgide (E)-2-[1-(2,5-dimethyl-3-furyl)-ethylidene]-3-isopropilidene
succinic anhydride was synthesized by three steps according to the liter-
ature [6].
[13] have also been studied in ILs. Nevertheless, there are no reports on
the photochromic behavior in ILs for colorants such as fulgides, for exam-
ple, Aberchrome 540™, which have been only studied on conventional
solvents (acetonitrile, toluene, etc.) [4, 6]. Considering the aforemen-
tioned it is interesting to study the influence of ILs on the photochemical
stability of this fulgide and the kinetic behavior of its photobleaching pro-
cess (ring opening and closing). To achieve this, the photoconversion of
the fulgide was studied in a series of ILs with different combinations of
cations and anions (Scheme 2). In addition, the results obtained in ILs
are compared to those obtained in conventional solvents (such as ben-
zene, toluene and acetonitrile).
2.3. Determination of Quantum Yield Photobleaching of Aberchrome 540™
For the irradiation, a Thorlabs' DC4100 and DC4014 four-channel
LED (Light emitting diode) controllers and two mounted LEDs of
455 nm (M455L3) and 365 nm (M365LP1) were used. Fulgide solution
in acetonitrile and ILs were prepared at a concentration of 6 × 10− M.
Each solution was placed in a quartz reactor and was irradiated with
UV/VIS light, LEDs, of 455 nm and 365 nm. This procedure converted
the amber E-form to the red C-form till the maximum conversion had
been attained as indicated by the stability of maximum absorption of
the red dye at λmax = 498 nm. The sample was then placed in a holder
and the temperature was regulated and kept at 25 °C and irradiated
with light of 455 nm for the reverse process (C → E).
5
2
. Experimental
2
.1. Materials and Instrumentation
All ionic liquids and conventional solvents were obtained from com-
mercial sources and were dried before use on a vacuum oven at 70 °C for
at least 48 h and stored in a dryer under nitrogen and over calcium
First we determined the radiant flux (I), Eq. (1), of the LED at 365 nm
with a brightness of 100% by using the Heller and Langan methodology
[4], assuming a Ф value in toluene of 0.2 in Eq. (1). With this
Scheme 2. Ionic liquids used in this study.

M.E. Aliaga et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 204 (2018) 125–130
127
information, it was possible to evaluate the fulgide quantum yields for
coloring at 365 nm with a 100% of brightness, with 2 min of irradiation.
ꢀ
ꢀ
I ¼ A V N
ð1Þ
ꢀ
−1
∅
ꢀt photons s
The same method was employed to determine the radiant flux (I) of
the LED at 455 nm with a 100% of brightness (using potassium
ferrioxalate as a standard actinometer) [14] and the fulgide quantum
yields for decoloring at 498 nm, with 6 min of irradiation.
2
.4. Photochemical Fatigue Resistance
Continuously-stirred solutions were photocolored and bleached
with alternate light emitted from a diode at 355 nm for photocoloration,
and at 455 nm for bleaching. The solutions were monitored by measur-
ing the decreasing or increasing absorbance at 500 nm using a HP-8453
diode array spectrophotometer over various periods of time.
3
. Results and Discussion
3
.1. Photochromic Behavior of Aberchrome 540™ in Ionic Liquids
The open form of Aberchrome 540™ had a light pale-yellow color
when it was dissolved either on conventional solvents (acetonitrile,
benzene and toluene) and on each one of the IL tested (see structures
in Scheme 2).
Fig. 1A–C show the absorption spectral change that Aberchrome
5
40™ undergoes by irradiation at 365 and 455 nm in the reaction
media. In particular, when a solution containing the fulgide in acetoni-
trile was irradiated at 365 nm till total conversion, the spectrum associ-
ated with the closed ring C-form show three absorption maximums at
2
10, 270 and 505 nm (Fig. 1A, red color spectrum). As expected, these
fulgide absorption bands, in acetonitrile, are in accordance with other
reports, which have attributed this spectrum to the closed form of the
fulgide [15]. Notwithstanding this, when this solution is irradiated at
4
55 nm, the close form opens to form the E-isomer of fulgide, with the
recovery of the initial spectrum (see Fig. 1A, black spectrum).
Aberchrome presents a similar absorption spectra in ILs (λmax of 505
to ∼520 nm, see Figs. 1 B–C, S1–S14) with small shifts in the spectral
maxima regarding conventional solvents. For the ILs where a
photoreversible process takes place there are no significant differences
in the absorption maximum of the E-form (350 nm). However, as
some of the ILs have strong absorptions at short wavelengths, it is not
possible to observe the structured absorption (black) that can be seen
in acetonitrile or toluene.
According to these results, it is important to note that the absorption
spectra maxima of the both forms of fulgide are similar in either con-
ventional solvents or the tested ILs. This similarity of solvatochromic
shifts could be due to the fulgide forms perceiving similar environ-
ments, irrespectively of the IL and how they interact with it. In fact,
other authors have reported that the observed spectral behavior of the
fulgide in the closed and open forms are in between those reported
for other photochromic dyes in polar solvents as acetonitrile and etha-
nol [10]. Therefore, the interaction with our ILs should be similar.
In relation to photoconversion quantum yields of Aberchrome 540™
in ionic liquid media (Table 1), these values are lower than those in ace-
tonitrile, but similar to other conventional solvents like toluene. In par-
ticular, the conversion quantum yield (E- to C-form) with 365 nm
excitation was 0.2 in toluene and between 0.1 and 0.2 in ILs. The C-to-
E-form conversion measured with 455 nm excitation is much more effi-
cient with quantum yields of 0.5 in acetonitrile and between 0.3 and 0.7
in ILs.
Fig. 1. Absorption spectra for Aberchrome 540™ in acetonitrile (A), [Bmim][BF
4
] (B) and
[
4
Bmim][DCA] (C) after irradiation at 365 nm (red spectrum) and after irradiation at
55 nm (black spectrum). (For interpretation of the references to color in this figure
legend, the reader is referred to the web version of this article.)
3.2. Kinetic Results of the Photoconversion of Aberchrome 540™ in Ionic
Liquids
With the aim of broadening the understanding of the interaction be-
tween Aberchrome 540™ and ionic liquids, the kinetic behavior of their
photo conversion (ring opening reaction), namely from C-form to E-
form was studied. The first-order rate constants (kobs) were measured
by following the disappearance of the C-form of the fulgide. The values

128
M.E. Aliaga et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 204 (2018) 125–130
Table 1
Rate constant values (kobs) of the photobleaching of the colored form and quantum yields
Φ) associated to both processes, photo conversion from C-form to E-form and the inverse
photobleaching reaction with each solvent parameter was correlated;
these results are shown in LSER 1 in Table 2.
(
process in different reaction media.
log ðkobsÞ ¼ logðk0Þ þ aα þ bβ þ sπꢀ
ð2Þ
obs/10− s-1a Quantum yield (ФC→E)b Quantum yield (ФE→C)c
3
Reaction media
k
Acetonitrile
Benzene
Toluene
5.42
7.25
9.41
5.31
6.57
5.50
8.27
7.20
6.57
7.55
5.88
6.69
6.74
0.19
0.24
0.23
0.15
0.15
0.10
0.15
0.05
0.06
0.45
0.23
–
0.16
0.19
0.20
0.15
0.16
0.15
0.16
0.15
0.16
0.12
0.10
–
As we can see in LSER 1, a treatment based on a multi-parametric re-
gression with Kamlet–Taft's solvent parameters failed (R = 0.60).
Therefore, to improve the correlation it was necessary to include other
parameters to account for all the experimental observations. Thus, the
[
[
[
[
[
[
[
[
[
[
[
[
[
Bmim][DCA]
Bmim][PF
6
]
square of the Hildebrand solubility parameter (δ2
H
) was considered. In-
terestingly enough, when a Hildebrand parameter is introduced into
Bmim][BF
4
]
Bmpyrr][NTf
Bmim][OTf]
2
]
∗
2
0 H
the multi-parametric regression: XYZ=XYZ + aα + bβ + Sπ + hδ ,
Etm
2 2
pN][NTf ]
the correlation improves considerably, LSER 2 (R = 0.92) (see Table 2).
In addition, LSER 2 shows a poor statistical significance of both hy-
drogen bond donating ability (α), and hydrogen bond accepting ability
Bmpyrr][OTf]
Bmim][NTf
Bm im][NTf
Hmim][NTf
2
]
2
2
]
2
]
0.15
0.11
–
0.10
0.13
–
(
β) parameters. Therefore, these are not affecting much the ring open-
ing. LSER 3 (Table 2) shows the high statistical weight of polarizability
π*) and Hildebrand parameters (δ2
). These results suggests that
Bmpyrr][DCA] 6.92
Bm
Bm
2
im][BF
im][OTf]
4
]
6.19
7.19
(
H
2
–
–
changes in the rate constants (kobs) of the photobleaching reaction of
Aberchrome 540™ would not be governed by hydrogen bonding inter-
actions, but rather by weaker interactions such as coulombic (π* param-
a
Each measurement was made in triplicate. Error in kobs is approximately 5%.
Using methodology reference ϕPotassium Ferrioxalate = 0.844 at 498 nm [12]. Time irra-
b
diation of 6 min, LED at 455 nm with a 100% of brightness, using Eq. (1).
c
eter) and likely excluded volume Van der Waals interactions (δ2
Using methodology of Heller and Langan, using ϕToluene = 0.2 at 365 nm [4]. Time
H
irradiation of 2 min, at LED at 365 nm with 100% of brightness using Eq. (1).
parameter), with a larger statistical weight.
In light of this, Fig. 2 shows a comparison between the experimental
value of kobs for the photobleaching reaction of fulgide versus the calcu-
of kobs of these reactions at 25 °C are shown in Table 1 and are found to
be slightly higher in each of the ILs in comparison to that obtained for
acetonitrile, with the exception of the [Bmim][DCA].
lated value of kobs by using LSER, when π* and δ2
parameters were in-
cluded in the plot, Fig. 2(A), and disregarding the Hildebrand
parameter (δ2
), Fig. 2(B).
Fig. 2(A) shows the robust predictable element when π* and δ
H
The first attempt to rationalize the kinetic results obtained was to
correlate the rate constants (kobs) of the photobleaching reaction of
Aberchrome 540™ (irradiation at 455 nm of the close form) with the
viscosity of the different solvents used in this study. However, as can
be expected, solvent viscosity has no major influence in the ring open-
ing quantum yield mainly because the ring opening does not imply a
bond rotation and hence solvent reordering. Therefore, other specific
factors, such as polarity and/or solute solvent interactions, would affect
the reaction rate.
In order to explain how the kobs of the photobleaching at 455 nm ab-
sorption of Aberchrome 540™ depends on the nature of the solvent, a
multiparametric linear solvation energy relationship (LSER) based on
Kamlet–Taft descriptors was used. This LSER separate the solvent polar-
ity into a hydrogen bond donating ability (α), hydrogen bond accepting
ability (β), and a combination of dipolarity and polarisability (π*) [16].
Each parameter was empirically obtained and reported in a wide
range of solvents, including ionic liquids [17]. (see Table S1, in Supple-
mentary Material).
H
2
H
parameters are used in combination to account for the kobs values
found for the studied photobleaching at 455 nm reaction. The impor-
tance of the Hildebrand parameter on the photobleaching reaction for
Aberchrome is not surprising because this reaction involves a process
of rearrangement of the fulgide, resulting from a change in the size of
the cavity of the solvent where the substrate resides during the course
of a reaction. It is important to mention that no correlation with the vis-
cosity of each ILs has been found. This result is consistent with other
studies, which mention that the macroscopic solvent properties, such
as viscosity, are not always adequate in order to explain some spectro-
scopic behaviors in ILs [19]. In such case, for microscopic ILs environ-
ment, the term microviscosity arises as a parameter to be considered,
which depends on the solute and the solvent interactions. Therefore,
considering the results of the multiparametric regressions (Fig. 2), the
molecular confinement in ILs of the Aberchrome would dependent not
only of the Hildebrand relevant parameter (in particular molar volume)
but also of its local viscosity of the microenvironment surrounding the
dye molecules.
As can be expected ILs behave differently to conventional sol-
vents. Therefore, the Kamlet Taft's correlation cannot be compara-
ble for ILs and conventional solvents. Moreover, the polarity
concept should be taken into account with particular care for ILs
3.3. Photochemical Fatigue Resistance
[
18].
Eq. (2) shows a generalized LSER, where the logarithm of the rate
The photochemical fatigue resistance of Aberchrome 540™ in each
IL was estimated upon repeated UV and vis light exposure cycles. Addi-
tionally, these responses with the resistance of fulgide in conventional
solvents were compared.
constants (kobs) is a variable term proportional to free energy of the
photobleaching ring opening reaction of Aberchrome 540™. Thus, a
statistically relevant result was obtained when log (kobs) of the
Table 2
2
Statistical data from the multiparametric regression procedure including α, β and π* Kamlet–Taft's parameters and Hildebrand solubility parameter (δ
photobleaching reaction of Aberchrome 540™.
H
), for the rate constants (kobs) of the
LSER
log (kobs
)
k
0
ac
bc
sc
h/10–3c
Fa
Rb
1
2
3
log(kobs
log(kobs
log(kobs
)
)
)
−1.03(0.28)
−0.78(0.18)
−0.92(0.13)
−0.0048(0.08)
0.045(0.047)
–
0.03(0.11)
0.069 (0.062)
–
−1.12(0.31)
−1.58(0.24)
−1.38(0.16)
–
7.2
25
55
0.60
0.92
0.94
3.08(0.95)
2.65(0.08)
a
Statistical F.
Correlation coefficient.
Standard deviations are given in parentheses.
b
c

M.E. Aliaga et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 204 (2018) 125–130
129
(A)
(B)
Fig. 4. Photochemical fatigue resistance of Aberchrome 540™ in some representative
studied IL's.
-1
ln (kobs/s ) experimental
Fig. 2. Double logarithmic plot of kobs of the photobleaching reaction for Aberchrome
40™ (C-form to E-form) experimental form against kobs calculated by LSER 3. (A) From
5
reference point; these solvents show an excellent fatigue resistance
according to the literature. On the other hand, moderate resistance
2
LSER 3 (Table 2), considering π* and δ and neglecting α and β parameters. (B) From
H
2
H
LSER 1 (Table 2), without considering δ .
was obtained when [Etm
2
pN][NTf
2
], [Bmpyrr][OTf], [B
2
mim][NTf
2
],
2
[B mim][OTf] were studied as a reaction media (Group II). Low fatigue
As shown in Fig. 3, some photochemical cycles obtained for the
fulgide in acetonitrile (A), [Bmim][OTf] (B) and [Bmpyrr][DCA] (C) are
presented. Interestingly, these results demonstrate that the fulgide
shows a similar behavior in [Bmim][OTf] in comparison to conventional
solvents, as acetonitrile, used normally with this dye. In addition,
Aberchrome 540™ can resist over 100 min of continuous cycles of irra-
diation in [Bmim][OTf]. Similar behavior was observed in the presence
resistances were observed for the following ILs: [Bmpyrr][NTf
[B mim][BF ], [Bmim][NTf ], [Hmim][NTf
2
],
2
4
2
2
], [Bmim][DCA] and
[Bmpyrr][DCA] (namely, Group III). Therefore, it is proposed that de-
pending on the ILs used, it is possible that the stabilization of different
forms of the fulgide can be controlled. This information is very impor-
tant in terms of choosing the appropriate ILs for a specific photochemi-
cal reaction, particularly if the media is less stable.
of [Bmim][PF
6
] and [Bmim][BF
4
] (see Supplementary Material). This
According to these results, it was found that the reversible changes
of the Aberchrome 540™ were sensitive to the nature of the cation-
suggests that these ILs are the most stable media and the fulgide could
be used as actinometer in its.
anion pair. The latter could be associated with the molar liquid volume
3
The opposite affect was observed when, for example, [Bmpyrr][DCA]
was used as a reaction media. Fig. 3C shows that the fulgide has low
photochemical fatigue resistance, losing almost 35% of its initial absor-
bance during the first irradiation cycle. Therefore, it might only resist a
maximum of 6 photochemical cycles before being converted into
another form. It is important to mention that, the same behavior was
observed for the IL [Bmim][DCA], which could be promoting the forma-
tion of the Z-form of the fulgide. Results for other tested ionic liquids are
presented in the Supplementary Material (Figs. S15–S30).
(V˜ (Å )) of each IL. In particular, in the case of [Bmim][DCA] and NTf
2
3
3
(~500 Å ) in comparison with [Bmim][PF
6
] and [Bmim][BF
4
] (~300 Å )
the first ILs may inhibit the photo conversion from the E-form to C-
form probably through a space orbital interaction that stabilizes the Z-
form. However, for ILs with a relatively low molar liquid volume, the
photo reversibility is favored. This is in line with the correlation men-
tioned above regarding the importance of the Hildebrand parameter
on the photobleaching reaction for Aberchrome.
Once the photochemical cycles of fulgide in the presence of each ILs
have been assessed, it is possible to describe the response of all solvents
together. As shown in Figs. 4 and S31, the tested ILs can be grouped ac-
cording to how they can affect the photochemical resistance of the
fulgide. Thus, the higher photochemical fatigue resistances of fulgide
were observed in the presence of the ILs [Bmim][BF ], [Bmim][PF ]
4 6
and [Bmim][OTf] (Group I). As a control experiment, conventional sol-
vents such as acetonitrile, benzene and toluene were incorporated as a
4. Conclusions
The photo conversion of the Aberchrome 540™ in Ionic Liquids
media was evaluated in terms of its spectroscopic, photochromic and
kinetic performance. Results demonstrated that in the case of
photoreversibility process in ILs there are no differences between
them and conventional solvents, relative to the maximum of absorption
of both forms. In relation to the kinetic study, a good multi-parametric
Fig. 3. Reversible cycles of the Aberchrome540™ in some representative solvents: Acetonitrile (A), [Bmim][OTf] (B) and [Bmpyrr][DCA] (C), at 25 °C.

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M.E. Aliaga et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 204 (2018) 125–130
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2
rameter and Hildebrand solubility parameter δ
H
.
The present work, also shows that in most cases, ILs do not favor the
Aberchrome 540™ reversibility, from the E-form to the C-form. How-
[
ever, it was found that using [Bmim][BF
4 6
], [Bmim][PF ] and [Bmim]
[
OTf] as a reaction medium, the reversibility is similar to conventional
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within imidazolium ionic liquids: a thermodynamic study using photochromic mo-
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solvents and thus Aberchrome 540™ is promising actinometer for use
in these ILs and therefore evaluate quantum yields of other photochem-
ical reaction in theses media.
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Acknowledgments
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A.D. Baker, A. Casadevell, H.D. Gafney, M. Gellender, Photochemical reactions of
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FONDECYT Grant #1170976, 1150567 and ICM-MINECON, RC-
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(
VRI-PUC) Puente N° P1708/2017.
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Appendix A. Supplementary data
[
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