Systematic variation of thiophene substituents in photochromic spiropyrans

Article abstract of DOI:10.1039/c7pp00057j

Spiropyrans are notable among different classes of photochromic compounds due to their large structural and electronic transformation upon isomerization. In order to parlay the electronic differences associated with the two isomeric forms into a materials based switch, the spiropyran ultimately requires a covalent attachment through a conjugated pathway. In this work a synthetic method was developed to incorporate spiropyran (SP) into thiophene based materials. A series of compounds with a systematic variation of substituents were synthesized (SP-T, SP-T-Br, SP-T-T, SP-T-T-T and SP-T-T-T-T-SP) and their photochromism in both polar (methanol) and non-polar (toluene) solvents were studied. These compounds showed a systematic variation of photochromic properties.

Full text of DOI:10.1039/c7pp00057j

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Systematic variation of thiophene substituents in photochromic
spiropyrans
Received 00th January 20xx,
Accepted 00th January 20xx
Dushanthi S. Dissanayake, Gregory T. McCandless, Mihaela C. Stefan and Michael C. Biewer*
DOI: 10.1039/x0xx00000x
Spiropyrans are notable among different classes of photochromic compounds due to their large structural and electronic
transformation upon isomerization. In order to parlay the electronic differences associated with the two forms into
materials based switch, the spiropyran ultimately requires a covalent attachment through a conjugated pathway. In this
work a synthetic method was developed to incorporate spiropyran (SP) into thiophene based materials. A series of
compounds with a systematic variation of substituents were synthesized (SP-T, SP-T-Br, SP-T-T, SP-T-T-T and SP-T-T-T-T-SP)
and their photochromism in both polar (methanol) and non-polar (toluene) solvents were studied. These compounds
www.rsc.org/
showed
a
systematic
variation
of
photochromic
properties
to thiophene based materials. Despite the few reports on
attaching thiophene based moieties to SP via indoline
nitrogen,10-12 a detailed study on photochromic properties of
thiophene based SP via other positions of SP is lacking.
Furthermore, it is very important to systematically vary
substituents and study them under identical experimental
conditions to allow a direct comparison of substituent effect
on photochromic properties. A very recent study by Louie and
co-workers emphasized the importance of this concept and
demonstrated the effect of electron withdrawing and donating
substituents on C-O bond lability and therefore the
photochromic properties.13 In this study we systematically
varied the thiophene substituents in photochromic SP at the 5-
position and studied their kinetics parameters. This attempt is
Introduction
Photochromism is the ability of a molecule to undergo
reversible structural changes upon absorption of light. These
compounds attract considerable attention as light is an ideal
and selective external trigger signal. Among different classes of
photochromic materials indoline spiropyrans (SPs) are notable
for their high sensitivity (towards thermo, photo, acidic and
ionic multi responsive systems), resolving power, exhibiting
photochromic properties in solution, in polymeric matrices and
even in solid state, which is very convenient for their practical
applications.1-3 Another unique feature of SPs is that the
photo isomerization initiates a significant change in the electric
dipole moment of SPs between closed and open forms (6.4 D
for SP-closed and 13.9 D for MC-open) which is useful in
expected to give
a
fundamental understanding of
photochromic properties of SP when attached to a thiophene
based chain.
macroscopic scale switchable molecular devices.4,5
The
growing interest of using these materials in organic electronic
devices is evident by the number of recent reviews published
in this field.6-8
Results and discussion
Well known thiophene based semiconducting polymers such
as poly(3-hexylthiophene) have been studied in blends with
SPs in organic field effect transistors.4,9 However, the major
challenge lies with phase separation of SPs within these
blends. Therefore, it is very important to design and synthesize
new SPs with improved properties such as excellent
reversibility, stability of both isomers, fast response, low
fatigue and excellent blending ability. We believe that this
could be successfully achieved by covalently attaching the SP
Thiophene substituted spiropyran (SP-T)
Indoline SP can be synthesised by condensation of indolium
salts with o-hydroxy aromatic aldehydes in the presence of a
base (or methylene bases with o-hydroxy aromatic aldehydes
).14 To incorporating SP as a pendent group into thiophene
based material via a conjugated pathway we modified the
indolium iodide moiety with thiophene substituent and
reacted with nitro salicylaldehyde which is a well-known o-
hydroxy aromatic aldehyde used in SP synthesis. As shown in
scheme 1 compound
synthesis of
isopropylmethylketone in the presence of sulfuric acid.15
Suzuki coupling between compound and thiophene-3-
1
was obtained through a Fischer indole
4-bromophenyl hydrazine with
A
1
boronic acid in the presence of tetrakis(triphenylphosphine)-
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palladium(0) catalyst followed by
a
methylation yielded Monomrominated derivative (SP-T-Br)
compound
work to obtain higher yields.16 The photochromic compound
SP-T was then synthesized by reacting compound with 2-
2. This procedure is a modification to Guido et al.
SP-T-Br was obtained through bromination of SP-T with N-
bromosuccinimide (scheme 2). When a thiophene moiety is
incorporated in SP via the 5-position, monobromination
selectively occurred at the 2-position of thiophene. Crystal
structures of SP-T-Br is given in figures 2 (1D, 2D-NMR analysis
and structure report data are given in supporting information)
2
hydroxy-5-nitrobenzaldehyde in the presence of triethylamine.
Crystal structures of SP-T is given in figures 1 (1D, 2D-NMR
analysis and structure report data are given in supporting
information)
SP
SP
Br
NBS
N
S
S
0 °C - RT
THF
B(OH)2
SP-T
SP-T-Br
Br
O
Yield 99 %
H2SO4
Br
S
N
S
EtOH
Reflux
Pd(PPh3)4
aq. K2CO3
Scheme 2: Synthesis of SP-T-Br
NHNH2.HCl
1,2-dimethoxyethane
CH3I
1
CH3CN
Reflux
Yield 96 %
NO2
HO
I
O
N
N
H
NO2
O
N(CH2CH3)3
CH3OH
S
SP-T
S
Yield 57 %
Yield 21 %
2
Scheme 1: Synthesis of SP-T
(a)
Figure
2
:
Crystal structure of SP-T-Br indicating ratio be-tween the two
thiophene conformations in approximately 70:30 (the major conformation is
indicated with solid bonds and the minor conformation is indicated with dashed
bonds).
Systematic variation of thiophene substituents
A series of compounds, SP-T-T, SP-T-T-T and SP-T-T-T-T-SP
were synthesized by Stille coupling reactions of SP-T-Br using
tetrakis(triphenylphosphine)-palladium (0) as the catalyst
(Scheme 3) and their photochromic properties were studied. A
model SP compound that has a bromine substituted at the 5-
position of the indoline instead of thiophene (SP-Br) was also
prepared for comparison (supporting information).
(b)
Scheme 3: Synthesis of SP-T-T, SP-T-T-T and SP-T-T-T-T-SP
Photochromic properties
Photochromism of SP strongly depends on the structure of the
compound and the medium, therefore a common polar
solvent methanol (ε ~ 33) and non-polar solvent Toluene (ε = ~
2) have been used in this study. All the experiments were
performed in identical experimental conditions of 1×10-5
M
solutions. The solutions were freshly prepared prior to each
Figure 1: (a) Crystal structure and (b) partial unit cell representation of SP-T.
2 | J. Name., 2012, 00, 1-3
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experiment by stirring each compound overnight in the form is a hybrid of these resonance forms.17,18 When a polar
respective solvent. solvent is used as the medium, zwitterionic state is
The structure of SP-T and its isomerization is shown in Figure 3 preferentially stabilized through hydrogen bonding with the
(a). The molecule is composed of an indoline with an attached solvent, while the quinoidal form is favored in non-polar
thiophene and a chromene moiety (nitro-substituted SP were solvents. The higher absorbance that we have observed in
studied because they are the most common SP used, and toluene compared to that in methanol in Figure 5b could be
therefore, the results in this study may be compared to other due to this favorable quinoidal form.
systems). These two heterocyclic parts are linked together MC isomer tends to aggregate in non-polar solvents and this
through a common spiro junction and are in two orthogonal behavior was observed predominantly with nitro substituted
planes (see partial unit cell representation in figure 1b). In SPs.3,19 However, SP molecule which has the exact same
solution, SP shows an absorption spectrum below 400 nm. A substituents except a H at 5-position showed an absorbance
absorption in this range cleaves the C-O bond to yield the band at 605 nm and a shoulder at 580 nm for a solution of MC
colored merocyanine (MC) isomer.17 When a SP-T solution was in toluene. The 605 nm band was assigned to monomer MC
photolyzed with a 500 W Oriel Hg arc lamp containing a 334 and shoulder at 580 nm was assigned to dimer MC.19 A similar
nm line filter, a maximum absorbance was noted at 540 nm (in peak pattern was observed in toluene with 5-position
methanol) and 616 nm (in toluene). Typically, all the studied substituted SPs used in this study (figure 4, 5). The position of
compounds showed similar behavior upon irradiating with UV the shoulder did not change with increase in thiophene units
light except SP-T-T-T-T-SP which showed a λmax of the MC (figure 4).
isomer in methanol at 545 nm (figure 4a, denoted by an Strong H-bonding and solute-solvent interactions in polar
arrow).
solvents give less tendency for aggregation. Therefore, in
methanol we have not observed any additional peak or
shoulder peak in any of the compounds that we have studied.
The position of the λmax in methanol did not change with
increase in thiophene units whereas, red shift of λmax in SP-T-T-
T-T-SP could be attributed to charge distribution along the π-
electron system which influences the polarity and H-bonding
ability of the molecule.20
(a) 0.6
0.5
(b) 0.6
0.5
(c)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
SP-Br
Methanol
Toluene
SP-T
SP-T-Br
0.4
0.4
0.3
0.3
0.2
0.2
0.1
0.1
0.0
0.0
400 450 500 550 600 650 700
400 450 500 550 600 650 700
400 450 500 550 600 650 700
Wavelength(nm)
Wavelength(nm)
Wavelength(nm)
(d)0.6
(e) 0.6
(f)
0.6
SP-T-T-T
SP-T-T-T-T-SP
SP-T-T
0.5
0.4
0.3
0.2
0.1
0.0
0.5
0.4
0.3
0.2
0.1
0.0
0.5
0.4
0.3
0.2
0.1
0.0
Figure 3: Isomerization of SP-T (a) Optical absorbance of photomerocyanine (MC) of
SP-T (b) in methanol (c) in toluene. All spectra are obtained upon irradiating 1×10-5
M
solutions using a mercury arc lamp with a 334 nm line filter.
400 450 500 550 600 650 700
400 450 500 550 600 650 700
400 450 500 550 600 650 700
Wavelength(nm)
Wavelength(nm)
Wavelength(nm)
(b)
(a)
SP-Br
SP-T
SP-T-Br
SP-T-T
SP-T-T-T
SP-Br
SP-T
SP-T-Br
SP-T-T
SP-T-T-T
SP-T-T-T-T-SP
0.8
0.6
0.4
0.2
0.0
0.8
Methanol
Toluene
Figure 5: Comparison of maximum optical absorbance of photomerocyanines in
methanol and in toluene, All spectra are obtained upon irradiating 1×10-5 M solutions
using a mercury arc lamp with a 334 nm line filter.
0.6
0.4
0.2
0.0
SP-T-T-T-T-SP
The MC state is thermally unstable and the rate of conversion
to the SP state can be controlled by stabilizing the MC in a fluid
media through electrostatic interactions or in a rigid media via
hindering the conformational mobility. Our group has studied
various aspect in this regard.21-26 In the current study, thermal
decay was measured in polar and non-polar solvents. Typically,
the measurements were collected by photoexcitation of the
colorless SP to MC and taking an absorbance reading of the
300 400 500 600 700 800
Wavelength (nm)
300
400
500
600
700
800
Wavelength (nm)
Figure 4: Maximum optical absorbance of photomerocyanine (a) in methanol (b) in
toluene. All spectra are obtained upon irradiating 1×10-5 M solutions using a mercury
arc lamp with a 334 nm line filter.
Even though the mechanism of the ring opening reaction of SP
has been broadly studied and a few mechanisms have been
suggested. A proposed theory is that this reaction represents a
heterolytic C-O bond cleavage causing two mesomeric forms
that are a zwitterionic form or quinoidal form and the final MC
λ
max of the MC as it decays every 15-30 s over 90-180 s (figure
S41 in supporting information). In both polar (methanol) and
non-polar(toluene) solvents MC showed a first order decay.
Table 1 summarizes the decay rates in each solvent. The decay
rates in methanol are relatively slow due to the stabilization of
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the polar MC through hydrogen bonding with the solvent.23 chain length. This might reflect the more conjugated
Upon increasing the number of thiophene units gradually (SP-T thiophene chain stabilizing either the changed zwitterionic or
to SP-T-T to SP-T-T-T) the decay rates significantly lowered in quinoidal MC form. When a bromine atom was connected at
methanol. At least with the short thiophene chains in this 5-position
study, the decay rate decreased with an increasing thiophene
of
Table 1. Half-lives of Spiropyran (SP) decay in various solventsa
t1/2(s)
Average rate (s-1)
Toluene
Compound
Methanol
Toluene
Methanol
Toluene
(λmax = 575 nm)
(λmax = 540 nm)
(λmax = 616 nm)
(λmax = 540 nm)
(λmax = 616 nm)
SP-Br
SP-T
520±22
293±42
14±3
20±3
21±2
21±3
19±4
18±6
0.0013
0.0024
0.052
0.035
0.034
0.034
0.038
0.043
0.052
0.033
0.034
0.033
0.037
0.038
SP-T-Br
755±119
404±50
0.00093
0.0017
SP-T-T
SP-T-T-T
SP-T-T-T-T-SP
1100±95
1045±95b
0.00063
0.00067b
aSamples were run with a 1 × 10-5 M solutions and the recorded values are an average of three runs, Irradiated for the first time.
bMeasured at 545 nm
indoline moiety (SP-Br) the thermal decay rate was slower distilled in the presence of calcium hydride under nitrogen and
than with one thiophene substituent (SP-T) because bromine dried over molecular sieves before use.
can act as an electron donating group stabilizing positive 1H and 13C NMR spectra and all 2D-NMR analysis were
charge on indoline nitrogen on MC. SP-T-T-T-T-SP also showed recorded at room temperature using a Bruker AVANCE III 500
slow decay rate in methanol.
MHz NMR spectrometer, as indicated, and were referenced to
The decay rates in non-polar toluene solvent were several residual protio solvent (CHCl3: δ 7.26 ppm). The data are
orders of magnitude higher than in methanol and showed reported as follows: chemical shifts are reported in ppm on δ
relatively similar values irrespective of the compound. All scale, multiplicity (s = singlet, d = doublet, t = triplet, q =
compounds except SP-T-T-T-T-SP displayed similar decay rates quartet, m = multiplet). UV-visible absorption experiments
for the λmax peak at 616 nm and the shoulder peak at 575 nm were carried using an Agilent 8453 UV-vis spectrometer. HRMS
(figure S41b in supporting information). In SP-T-T-T-T-SP the analysis was performed with Shimadzu LCMS IT-TOF
shoulder peak at 575 nm showed a relatively slower decay rate instrument. Samples were re-suspended in CHCl3, vortexed
compared with that of 616 nm peak.
and injected (15 µL).
Photodegradation of the compounds were tested with
multiple irradiation in the same solution. After three Synthetic procedures
consecutive irradiations in methanol, SP-Br SP-T SP-T-Br SP-
T-T SP-T-T-T SP-T-T-T-T-SP showed average of 6 %, 7 %, 10 %,
,
,
,
,
,
Synthesis of 2,3,3-trimethyl-5-(thiophene-3-yl)-3H-indole –
Thiophene-3-boronic acid (0.76 g, 5.7 mmol) and 5-bromo-
2,3,3-trimethyl-3H-indole (1.0 g, 4.2 mmol) were dissolved in
1,2-dimethoxy ethane (20 mL) in a 100 mL three-necked round
bottomed flask equipped with a reflux condenser. Nitrogen
was bubbled through this solution for 15 min prior to the
addition of potassium carbonate in water (1.6 g, 12 mmol in
6.0 mL of water). Nitrogen was bubbled through this solution
10 %, 6 %, 9 % photodegradation relative to the first
irradiation respectively (Table S1 in supporting information). It
was encouraging to observe photochromism in the bulky SP-T-
T-T-T-SP even after multiple cycles of irradiation.
Experimental
Materials and methods
for further
5
min prior to the addition of
tetrakis(triphenylphosphine)-palladium(0) (0.13 g, 0.11 mmol).
The reaction mixture was allowed to reflux under nitrogen for
12 h and then was cooled down to room temperature,
quenched with deionized water, extracted with ether dried
over anhydrous MgSO4 and evaporated under reduced
pressure. The crude product was used in the next step directly
without further purification. (M+ = 241.1)
All commercial chemicals were purchased either from Sigma
Aldrich Chemical Co. LLC. or from Fisher Scientific Co. LLC. and
were used without further purification unless otherwise noted.
All glassware and syringes were dried at 120 ᵒC for at least 24
h before use and cooled in a desiccator. Tetrahydrofuran (THF)
and toluene were dried over sodium/benzophenone ketyl and
freshly distilled under nitrogen prior to use. Acetonitrile was
4 | J. Name., 2012, 00, 1-3
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Synthesis of
ARTICLE
1,2,3,3-tetramethyl-5-(thiophene-3-yl)-3H- 7.40(dd, 1H), 7.30(m, 2H), 7.04(d, 1H), 6.93(d,1H), 6.81(d, 1H),
indole-1-ium-iodide (2) - 2,3,3-trimethyl-5-(thiophene-3-yl)- 6.60(d, 1H), 5.86(d, 1H), 2.78(s, 3H), 1.33(s, 3H), 1.23(s, 3H)).
3H-indole (1.0 g, 4.1 mmol) was dissolved in anhydrous 13C-NMR (CDCl3, 500 MHz;159.705, 147.233, 141.473, 141.032,
acetonitrile (20 mL) in a 100 mL three-necked round bottomed 136.217, 129.184, 128.388, 128.366, 126.625, 125.926,
flask equipped with a reflux condenser and kept under 125.606, 122.724, 122.171, 121.470, 118.632, 115.546,
nitrogen prior to the addition of methyl iodide (1.2 g, 8.7 107.256, 106.718, 106.373, 52.34, 28.89, 25.99, 20.01).
mmol). The reaction mixture was allowed to reflux overnight
Synthesis of 5′-([2,2′-bithiophene]-3-yl)-1′,3′,3′-trimethyl-6-nitro
under nitrogen. The solvent was then evaporated under
reduced pressure and the residue was treated with ethyl
acetate (100 mL). The final reddish color solid was collected by
filtration and washed with ethyl acetate to obtain the product
(0.96 g, 2.5 mmol, 57 %)). 1H-NMR (DMSO-d6, 500 MHz; 8.22(d,
1H), 8.08-8.07 (dd, 1H), 8.00-7.98(dd, 1H), 7.92 (d, 1H), 7.73-
7.72(dd, 1H), 7.70-7.69(dd, 1H), 3.98 (s, 3H), 2.75(s, 3H),
1.56(s, 6H)). 13C-NMR (CDCl3, 500 MHz; 195.98, 142.94,
141.42, 140.60, 136.77, 128.11, 126.89, 123.15, 121.45,
115.98, 54.43, 35.13, 22.28, 14.46).
spiro[chromene-2,2′-indoline] (SP-T-T) -
5'-(2-Bromothiophen-3-yl)-1',3',3'-trimethyl-6-
nitrospiro[chromene-2,2'-indoline] (50mg, 0.10 mmol) was
dissolved in dry toluene (10 mL) in a 100 mL three-necked
round bottomed flask equipped with a reflux condenser and 2-
(tributylstannyl) thiophene ( 0.03 mL, 0.10 mmol) was added
under nitrogen and nitrogen was bubbled through this
solution for 15 min prior to the addition of
tetrakis(triphenylphosphine)-palladium(0) (12 mg, 0.01 mmol).
The reaction mixture was allowed to reflux under nitrogen for
24 h, cooled to room temperature, quenched with acidified
deionized water (50 mL) and extracted with diethyl ether (50
mL × 3). Combined organic layers were washed with deionized
Synthesis of 1′,3′3′-trimethyl-6-nitro-5′-(thiophene-3-yl)spiro
[chromene-2,2′-indoline] (SP-T)
-
1,2,3,3-Tetramethyl-5-
(thiophene-3-yl)-3H-indole-1-ium-iodide (0.84 g, 2.2 mmol)
and 2-hydroxy-5-nitrobenzaldehyde (0.38 g, 2.2 mmol) was
kept in a 100 mL three-necked round bottomed flask equipped
with a reflux condenser and kept under nitrogen for 10 min
prior to the addition of methanol (100 mL). Four drops of
triethylamine were added at room temperature and the
reaction mixture was allowed to reflux gently for 3 h under
nitrogen, allowed to cool to room temperature, quenched in
deionized water and extracted with ethyl acetate (100 mL x 3).
The combined organic layer was washed with deionized water
(100 mL x 3), dried over magnesium sulfate and the solvent
was evaporated under reduced pressure. The crude was
water (50 mL
× 3), dried over anhydrous MgSO4 and
evaporated under reduced pressure. The crude was purified by
a column chromatography using ethyl acetate:hexane (1:4) as
the eluting solvent to obtain the product as a brownish solid
1
(47 mg, 0.097 mmol, 97 %). H-NMR (CDCl3, 500 MHz; 8.02(m,
2H), 7.25(s, 1H), 7.22(dd, 1H), 7.18(d, 1H), 7.10(d, 1H), 7.04(m,
2H), 6.94(m, 2H), 6.80 (d, 1H), 6.54(d, 1H), 5.84 (d, 1H), 2.77(s,
3H), 1.21(s, 3H), 1.15(s, 3H)). 13C-NMR (CDCl3, 500 MHz;
159.75, 147.03, 140.99, 139.51, 136.43, 136.18, 130.54,
130.49, 128.75, 128.27, 127.61, 126.96, 126.50, 125.89,
125.51, 123.81, 123.01, 122.72, 121.57, 118.66, 115.51,
106.79, 106.37, 52.24, 28.87, 25.80, 19.90). HRMS (ESI) m/z
calcd for C27H22N2O3S2+ (M + H)+ 487.1145, found 487.1148.
purified
by
column
chromatography
using
ethyl
acetate:hexane (1:4) as the eluting solvent. The pure
compound was obtained as a yellow crystalline solid (0.18 g,
0.46 mmol, 21 %, MP = 222-225 ˚C). 1H-NMR (CDCl3, 500 MHz;
8.03 (m, 2H), 7.45(dd, 1H), 7.37(m, 2H), 7.34(m, 1H),7.31(m,
1H), 6.93(d, 1H), 6.78(d, 1H), 6.58(d, 1H), 5.87(d, 1H), 2.77(s,
3H), 1.34(s, 3H), 1.23(s, 3H)).13C-NMR (CDCl3, 500 MHz; 159.74,
147.07, 142.83, 141.02, 136.79, 128.38, 128.22, 126.36,
126.24, 125.94, 125.93, 122.73, 121.45, 120.08, 118.65,
118.34, 115.51, 107.22, 106.47, 52.34, 28.97, 25.97, 19.99).
Synthesis of 5 -([2,2
′:5′,2′′
′
-terthiophene]-3-yl)-1
′,3′,3′
-trimethyl-6-
nitrospiro[chromene-2,2′-indoline] (SP-T-T-T) -
5'-(2-bromothiophen-3-yl)-1',3',3'-trimethyl-6-
nitrospiro[chromene-2,2'-indoline] (50 mg, 0.10 mmol) was
dissolved in dry toluene (10 mL) in a 100 mL three-necked
round bottomed flask equipped with a reflux condenser and
[2,2′-bithiophene]-5-yltributylstannane (45.5 mg, 0.10 mmol)
was added under nitrogen and nitrogen was bubbled through
this solution for 15 min prior to the addition of
tetrakis(triphenylphosphine)-palladium(0) (12 mg, 0.01 mmol).
The reaction mixture was allowed to reflux under nitrogen for
24 h, cooled to room temperature, quenched with acidified
deionized water (50 mL) and extracted with diethyl ether (50
mL × 3). Combined organic layers were washed with deionized
Synthesis of 5'-(2-bromothiophen-3-yl)-1',3',3'-trimethyl-6-
nitrospir[chromene-2,2'-indoline] (SP-T-Br) - 1′,3′3′-Trimethyl-
6-nitro-5′-(thiophene-3-yl)spiro[chromene-2,2′-indoline](45
mg, 0.11 mmol) was dissolved in freshly distilled
tetrahydrofuran (30 mL) in a 100 mL round bottomed flask
prior to the addition of N-bromosuccinimide (20 mg, 0.11
mmol) at 0 °C over a period of 15 min. The reaction mixture
was allowed to stir for 2 h while maintaining the temperature
between 0 °C and room temperature. After 2 h the reaction
mixture was quenched with deionized water and extracted
with diethyl ether. Combined organic layer was washed with
deionized water, dried over MgSO4 and evaporated under
reduced pressure to obtain the crude as a yellow solid. (62 mg,
MP = 209-215 ˚C) 1H-NMR (CDCl3, 500 MHz; 8.03(m, 2H),
water (50 mL
× 3), dried over anhydrous MgSO4 and
evaporated under reduced pressure. The crude was purified
through column chromatography using ethyl acetate:hexane
(1:4) as the eluting solvent to obtain the product as a brownish
solid (33 mg, 0.058 mmol, 58 %). 1H-NMR (CDCl3, 500 MHz;
8.02(m, 2H), 7.24(m, 2H), 7.18(d, 1H), 7.07(m, 3H), 6.98(m,
3H), 6.91(d, 1H), 6.76(d, 1H), 6.57(d,1H), 5.85(d,1H)). 13C-NMR
(CDCl3, 500 MHz; 159.76, 147.28, 140.99, 139.60, 137.31,
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J. Name., 2013, 00, 1-3 | 5
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ARTICLE
Journal Name
137.07, 136.24, 135.53, 130.69, 130.58, 128.76, 128.31,
127.77, 127.36, 126.87, 125.87, 124.36, 123.79, 123.54,
123.47, 123.25, 122.72, 121.55, 118.67, 115.50, 107.02,
106.42, 52.34, 28.91, 25.80, 19.87). HRMS (ESI) m/z calcd for
C31H24N2O3S3+ (M + H)+ 569.1022, found 569.1033.
Acknowledgements
The authors would like to thank the Welch Foundation (AT-
1740) and NSF (DMR-1505950) and for the financial support
provided for this research.
Synthesis of 3,3'''-bis(1',3',3'-trimethyl-6-nitrospiro[chromene-2,2'
-indolin]-5'-yl)-2,2': 5',2'':5'',2'''-quaterthiophene (SP-T-T-T-T-SP)
Notes and references
X-ray crystallography of SP-T (CIF) and SP-T-Br (CIF) is available
5'-(2-bromothiophen-3-yl)-1',3',3'-trimethyl-6-nitrospiro
[chromene-2,2'-indoline] (62mg, 0.13 mmol) and 5,5′-
bis(trimethylstannyl)-2,2′-bithiophene (32 mg, 0.065 mmol)
were kept under nitrogen in a 100 mL three-necked round
bottomed flask equipped with a reflux condenser prior to the
addition of dry toluene (10 mL). Nitrogen was bubbled through
this solution for 15 min prior to the addition of
tetrakis(triphenylphosphine)-palladium(0) (15 mg, 0.013
mmol). The reaction mixture was allowed to reflux under
nitrogen for 24 h, cooled to room temperature, quenched with
acidified deionized water (50 mL) and extracted with diethyl
ether (50 mL × 3). Combined organic layers were washed with
deionized water (50 mL × 3), dried over anhydrous MgSO4 and
evaporated under reduced pressure. The crude was purified
through column chromatography using ethyl acetate:hexane
(1:4) as the eluting solvent to obtain the product as a brownish
solid (24 mg, 0.025 mmol, 19 %). 1H-NMR (CDCl3, 500 MHz;
7.95 (m, 2H), 7.20 (d, 1H), 7.08(m, 2H), 6.90(m, 3H), 6.74(d,
1H), 6.55(d, 1H), 5.83(d, 1H), 2.77(s, 3H), 1.19(s, 3H), 1.14(s,
3H)), Acetone-d6, 500 MHz; 12 aromatic protons). HRMS (ESI)
m/z calcd for C54H42N4O6S4+ (M + H)+ 971.2060, found
971.2031.
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Conclusions
In conclusion, novel synthetic methods to incorporate SP in
thiophene based materials was successfully demonstrated and
their optical absorbance in polar (methanol) and nonpolar
(toluene) solvents was measured under identical experimental
conditions. When a thiophene moiety is incorporated in SP via
the 5-position, monobromination selectively occurred at the 2-
position of thiophene. Incorporating two to three thiophene
units at this position caused a decrease in the thermal decay
rate of the reverse reaction, thus increasing the half-life of MC
in methanol. When two SP units were connected at the two
ends of a quarterthiophene unit, thermal decay rate of the
reverse reaction was relatively low in methanol. These
compounds show 5-10 % photodegradation in methanol upon
three consecutive irradiations. All the compounds of interest
showed relatively similar thermal decay rate of the reverse
reaction in toluene. Overall, this study is expected to give a
new insight to different synthetic route to develop thiophene
based SP materials with improved photochromic properties.
The photochromic thiophene molecules are designed as
materials that are capable of actuated changes of their optical
and electronic properties.
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6 | J. Name., 2012, 00, 1-3
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A new synthetic method was developed to incorporate spiropyran into thiophene based materials
via a conjugated pathway. As the number of thiophene units increased thermal decay rate of the
reverse reaction decrease in methanol, thus increasing the half-life of merocyanine.

Photochemical & Photobiological Sciences
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