Disperse and disordered: A mexylaminotriazine-substituted azobenzene derivative with superior glass and surface relief grating formation

Article abstract of DOI:10.1039/c3tc32034k

Materials containing azobenzene chromophores exhibit photomechanical behaviors, including the formation of surface relief gratings (SRG) caused by irradiation with two interfering laser beams. While azo-functionalized polymers were extensively studied, small molecules offer the advantage of being monodisperse species, which translates into easier synthesis and purification, as well as more uniform behavior. A drawback is that they tend to crystallize and do not always form high-quality thin films. Glass-forming compounds incorporating azobenzene were previously synthesized in several synthetic steps and in low yield. Herein, a Disperse Red 1 (DR1) functionalized with a mexylaminotriazine group is synthesized in 94% yield using a simple and straightforward procedure. It shows both the ability to form extremely stable glassy phases, and the ability to form SRG in the solid state with growth rates and grating heights closely similar to DR1-functionalized polymers.

Full text of DOI:10.1039/c3tc32034k

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Materials Chemistry C
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Disperse and disordered: a mexylaminotriazine-
substituted azobenzene derivative with superior
glass and surface relief grating formation†
Cite this: J. Mater. Chem. C, 2014, 2,
841
a
b
c
Robert Kirby,ab Ribal Georges Sabat, Jean-Michel Nunzi and Olivier Lebel
*
Materials containing azobenzene chromophores exhibit photomechanical behaviors, including the
formation of surface relief gratings (SRG) caused by irradiation with two interfering laser beams. While
azo-functionalized polymers were extensively studied, small molecules offer the advantage of being
monodisperse species, which translates into easier synthesis and purification, as well as more uniform
behavior. A drawback is that they tend to crystallize and do not always form high-quality thin films.
Glass-forming compounds incorporating azobenzene were previously synthesized in several synthetic
steps and in low yield. Herein, a Disperse Red 1 (DR1) functionalized with a mexylaminotriazine group is
synthesized in 94% yield using a simple and straightforward procedure. It shows both the ability to form
extremely stable glassy phases, and the ability to form SRG in the solid state with growth rates and
grating heights closely similar to DR1-functionalized polymers.
Received 15th October 2013
Accepted 30th November 2013
DOI: 10.1039/c3tc32034k
www.rsc.org/MaterialsC
their behavior.15–20 However, the challenge with small molecules
is ensuring that they can form amorphous thin lms, and not
crystallize over time.15,16 To this end, azobenzene derivatives
Introduction
Compounds containing azobenzene moieties are well-known
for undergoing photoinduced cis–trans isomerisation.1 In the
solid state, this isomerisation at the molecular level translates
into macroscopic photomechanical behavior where molecules
migrate within the material as a result of diffusion of the azo
moieties.2 One particularly attractive consequence of this
phenomenon is the formation of surface relief gratings (SRG),
which is induced by the exposure to two interfering coherent
laser beams.3–5 Photoinduced SRG have been targeted for
several applications, including holographic data storage,6,7
distributed feedback lasers,8 optical sensors and coupling
devices,9,10 and light harvesting structures for photovoltaic
cells.11,12
capable of forming glassy phases have been synthesized by
various groups, and it was demonstrated that such materials
show photomechanical properties similar to those of their
polymer counterparts.21–26 On the other hand, current azo-
benzene-based molecular glasses based on triarylamines suffer
from certain limitations. Firstly, their synthesis requires
multiple steps and typically give modest overall yields, thereby
limiting their commercial potential. Second, some structural
screening is required to identify compounds with optimal glass-
forming ability (that will not crystallize upon heating or
standing).
In contrast to “conventional” molecular glasses, mexyl-
aminotriazine-based molecular glasses are more structurally
rigid due to higher symmetry, few degrees of rotational
freedom, strong conjugation of amino substituents to the
triazine ring, and the presence of groups that can engage in
hydrogen bonding according to predictable patterns.27,28
Despite this structural rigidity, these compounds typically show
excellent glass-forming ability and high to extreme resistance to
crystallization, in part due to their ability to participate in
hydrogen bonding in the solid state, and the high interconver-
sion barriers between conformations due to resonance.29–31
Both of these features increase the energy required to rearrange
the molecules into ordered structures, thereby frustrating
crystallization. These derivatives can be readily synthesized
from cyanuric chloride, 3,5-dimethylaniline, and other various
amines, by nucleophilic substitution.27,28 In addition, the
physical properties of the compounds, including their glass
While initial studies on the solid-state photophysical
behavior of azobenzene-based materials were performed using
polymers,13,14 small molecules possess several advantages,
being monodisperse species, they are typically easier to purify,
characterize and process, and show more reproducibility in
aDepartment of Physics, Royal Military College of Canada, Kingston, ON, K7K 7B4,
Canada. E-mail: sabat@rmc.ca; Fax: +1 613-541-6040; Tel: +1 613-541-6000 ext.
6721
bDepartment of Chemistry, Department of Physics, Queen's University, Kingston, ON,
K7L 3N6, Canada. E-mail: nunzijm@queensu.ca; Fax: +1 613-533-6669; Tel: +1
613-533-6749
cDepartment of Chemistry and Chemical Engineering, Royal Military College of
Canada, Kingston, ON, K7K 7B4, Canada. E-mail: Olivier.lebel@rmc.ca; Fax: +1
613-542-9489; Tel: +1 613-541-6000 ext. 3694
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c3tc32034k
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J. Mater. Chem. C, 2014, 2, 841–847 | 841

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transition temperatures (Tg), can be easily tuned by modifying 1266, 1252, 1189, 1159, 1113, 1065, 1037, 996, 972, 952, 934,
their molecular structures, and they can also be designed to 882, 842, 810, 735, 689 cmꢁ1; 1H NMR (300 MHz, CDCl3, 298 K) d
incorporate reactive groups that can be used to introduce other 7.22 (s, 2H), 6.84 (br s, 1H), 6.66 (s, 1H), 5.55 (br s, 1H), 5.02
functionalities.32
(br s, 1H), 3.47 (br s, 2H), 2.95 (d, 3J ¼ 5.3 Hz, 3H), 2.90 (t, 3J ¼
As it has been demonstrated that mexylaminotriazine units 5.3 Hz, 2H), 2.29 (s, 6H) ppm; 13C NMR (75 MHz, CDCl3) d 166.6,
can be attached to other core moieties to induce glass-forming 166.3, 164.3, 139.2, 138.1, 124.2, 117.9, 43.4, 41.5, 27.4, 21.4
ability in the latter,33 they are promising candidates for the ppm; HRMS (EI) m/z: [M]+ calcd. for C14H21N7: 287.1858, found:
design of novel azobenzene glasses. In the present study, a 287.1851.
novel azobenzene glass was synthesized in a two-stage, one-step
process, without the need for extensive purication, and in 94%
yield from a mexylaminotriazine precursor and Disperse Red 1,
which are both commercially available, and demonstrate both
the superior glass-forming properties of mexylaminotriazine
glasses and the ability to form surface relief gratings (SRG) with
characteristics and growth rates that are comparable to their
polymer counterparts.
Synthesis of DR1–glass 2
To a stirred suspension of N,N0-carbonyldiimidazole (0.773 g,
4.77 mmol) in dry THF (5 mL) in a dry round-bottomed ask
equipped with a magnetic stirrer was slowly added a solution of
Disperse Red 1 (1.00 g, 3.18 mmol) in dry THF (10 mL) at
ambient temperature, then the mixture was stirred for 18 h
under nitrogen atmosphere. CH2Cl2 and H2O were added, then
the layers were separated, and the organic layer was washed two
more times with copious amounts of H2O. The organic extract
was recovered, dried over Na2SO4, ltered, and the solvent was
evaporated. The crude residue was redissolved in THF (15 mL),
Experimental section
General
2-Mexylamino-4-methylamino-6-chloro-1,3,5-triazine
was
then
2-methylamino-4-mexylamino-6-(2-aminoethylamino)-
purchased from Solaris Chem, Inc. Ethylenediamine, Disperse
Red 1 and DR1–PMMA were purchased from Sigma-Aldrich,
N,N0-carbonyldiimidazole (CDI) was purchased from Oakwood
Chemicals, and all solvents were purchased from Caledon Labs.
All reagents were used without further purication. Reactions
were performed under ambient atmosphere unless otherwise
specied. Glass transition temperatures were determined with a
TA Instruments 2010 Differential Scanning Calorimeter cali-
brated with indium at a heating rate of 5 C min from 30 to
200 ꢀC. Values were reported aer an initial heating and cooling
cycle as the average of two heating runs. FTIR spectra were
acquired with thin lms cast from CH2Cl2 on KBr windows
using a Perkin-Elmer Spectrum 65 spectrometer. UV-visible
absorption spectra were acquired using a Hewlett-Packard 8453
spectrometer. NMR spectra were acquired on either a 400 MHz
Bruker AV400 or on a 300 MHz Varian Oxford spectrometer.
1,3,5-triazine (1.10 g, 3.82 mmol) was added and the mixture
was reuxed for 18 h. The solvent was evaporated, then 1 M
aqueous HCl was added, then the precipitated product was
collected by ltration and washed with 1 M aq. HCl and H2O
until the effluent was colorless. The residue was dissolved in
acetone, then CH2Cl2 and aq. NaHCO3 were added. The layers
were separated, the organic layer was dried over Na2SO4,
ltered, and the volatiles were thoroughly evaporated under
reduced pressure to yield 1.875 g of pure glass 2 (2.99 mmol,
94%). Tg 71 ꢀC; FTIR (CH2Cl2/KBr) 3560, 3272, 2973, 2925, 2869,
2853, 2066, 1688, 1647, 1626, 1600, 1584, 1566, 1511, 1440,
1420, 1389, 1376, 1355, 1334, 1309, 1244, 1189, 1153, 1131,
1102, 1041, 1014, 994, 960, 940, 917, 856, 821, 808, 776, 754, 726,
686 cmꢁ1; 1H NMR (400 MHz, DMSO-d6, 363 K) d 8.33 (d, 3J ¼ 9.3
Hz, 2H), 8.27 (br s, 1H), 7.90 (d, 3J ¼ 9.1 Hz, 2H), 7.83 (d, 3J ¼ 9.3
ꢁ1
ꢀ
3
Hz, 2H), 7.39 (s, 2H), 6. 90 (d, J ¼ 9.3 Hz, 2H), 6.84 (br s, 1H),
6.56 (s, 1H), 6.37 (br s, 1H), 6.30 (br s, 1H), 4.20 (t, 3J ¼ 6.0 Hz,
3
3
2H), 3.67 (t, J ¼ 6.0 Hz, 2H), 3.40 (q, J ¼ 7.1 Hz, 2H), 3.24 (q,
Synthesis of 2-methylamino-4-mexylamino-6-(2-
aminoethylamino)-1,3,5-triazine (1)
3J ¼ 6.0 Hz, 2H), 2.83 (d, J ¼ 4.8 Hz, 3H), 2.23 (s, 6H), 1.18 (t,
3
3J ¼ 7.1 Hz, 3H) ppm; 13C NMR (100 MHz, DMSO-d6) d 166.1,
163.9, 156.1, 151.5, 146.7, 142.7, 140.5, 136.9, 126.0, 124.8,
122.6, 122.4, 117.1, 111.5, 61.1, 48.7, 45.0, 40.4, 40.4, 27.2, 21.2,
11.9 ppm; UV-vis (CH2Cl2): lmax (3) 485 nm (28 000); HRMS (ESI)
m/z: [M + H]+ calcd. for C31H38N11O4: 628.3129, found: 628.3103.
2-Mexylamino-4-methylamino-6-chloro-1,3,5-triazine (50.0 g,
190 mmol) and ethylenediamine (100 mL) were added in a
round-bottomed ask equipped with a magnetic stirrer and a
water-jacketed condenser, then the mixture was heated at 80 ꢀC
for 18 h. Aer the mixture was allowed to cool down to room
temperature, the unreacted ethylenediamine was evaporated
under vacuum. The residue was dissolved in 4 M aqueous HCl,
Thin lm deposition
and the precipitate was removed by ltration and washed with Thin lms of DR1–PMMA and DR1–glass 2 were deposited by
H2O. NaOH pellets were added to the ltrate until the pH spin-coating using a Headway Research spin-coater. Solutions
became basic (>12), then the mixture was stirred for 30 min, at with a concentration of 3 wt% in CH2Cl2 were prepared and
which time the solvent was decanted. The precipitated product submitted to mechanical shaking for 1 hour, then ltered with a
was dissolved in CH2Cl2, dried over Na2SO4, ltered, and the 50 mm lter. Approximately 3 mL of solution were deposited on
solvent was thoroughly evaporated under reduced pressure to a BK7 glass slide with dimensions of 3 ꢂ 3 cm2, at a rate of 1000
ꢀ
yield 48.9 g of the title compound (170 mmol, 90%): Tg 58 C; rpm for 40 seconds. The lms were then dried in a Yamato ADP-
FTIR (CH2Cl2/KBr) 3402, 3275, 3195, 3134, 3013, 2945, 2920, 21 oven at 95 ꢀC for 5 minutes. Film thicknesses were measured
2866, 1587, 1566, 1549, 1520, 1440, 1396, 1358, 1323, 1300, with a Sloan Dektak II D prolometer (model 139961). Powder
842 | J. Mater. Chem. C, 2014, 2, 841–847
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X-ray Diffraction patterns of the lms were acquired with a
˚
Scintag X1 diffractometer using Cu Ka (1.54 A) between 2.5
and 50ꢀ (2q) and with a step of 0.02ꢀ and a scanning rate of
2.00ꢀ minꢁ1
.
Surface relief grating writing
SRG were formed on thin lms of DR1–PMMA and DR1–glass 2
by irradiating the samples with two interfering beams from a
Coherent Verdi diode-pumped laser (model 0174-525-52,
5 Watts), one directly incident, one reected upon a 3 ꢂ 3 cm2
Lloyd mirror placed orthogonally to the sample. The circularly
polarized incident beam was collimated, and passed through a
variable iris with a 1 cm diameter opening. This yielded a
grating area of approximately 0.39 cm2. First-order diffraction
intensity measurements were performed as described in the
Results section.
Scheme 1 Synthesis of glass precursor 1.
crystallization upon heating at a rate of 5 ꢀC minꢁ1. A repre-
sentative DSC scan is shown in Fig. 1a. Glass 1 thus shares the
glass-forming ability and high resistance to crystallization
shown by other derivatives of the mexylaminotriazine family,
even with a single arylamino substituent. It has been shown
previously that with a strong glass-promoting “headgroup” at
the 2-position of the triazine ring such as the methylamino
group, alkylamino groups can occupy the 4- and 6-positions
without loss of glass-forming ability.34
Atomic force microscopy
AFM scans were performed using a Pacic Nanotechnology
Nano-R O-020-0002 scanning probe microscope, in tapping
mode using mounted cantilever probes (Pacic Nanotechnology
model P-MAN-SICT-0).
To bond Disperse Red 1 to glass-forming precursor 1 in
a
covalent fashion, DR1 was rst reacted with
Results and discussion
Synthesis
Disperse Red 1 was selected as the dye because it is commer-
cially available, its photophysical and photomechanical prop-
erties have been extensively studied (in particular as DR1–
PMMA), and its remote hydroxy group can be functionalized
with minimal perturbation of the optical properties of the
chromophore. From a synthetic standpoint, the simplest route
to design a molecular glass substituted with a Disperse Red
1 moiety involves reacting the hydroxy group of DR1 with a
molecular glass already containing a functionalizable group.
Several glass-forming mexylaminotriazine derivatives contain-
ing reactive groups have been reported in recent work, some of
which can be readily made to participate in a covalent bond-
forming reaction with an alcohol.32 However, none of the
glasses reported so far gave satisfactory results: either the yields
were too low, expensive or highly toxic reagents were necessary,
a large excess of either DR1 or the glass were required, or
purication involved chromatography requiring large volumes
of solvents.
Carbamoylation with an amino-substituted glass was
selected as the synthetic method because it can be performed in
one step with roughly stoichiometric amounts of reagents and
under ambient conditions. As alkylamines are much more
reactive than anilines, new aminoethyl-substituted glass 1 was
synthesized from 2-mexylamino-4-methylamino-6-chloro-1,3,5-
triazine and excess ethylenediamine in 90% yield according to
Scheme 1. As compound 1 is soluble in aqueous acidic media, it
can be readily puried by dissolving the crude product in
aqueous HCl followed by neutralization.
Fig. 1 Representative differential scanning calorimetry scans of (a)
compound 1, and (b) DR1-substituted glass 2. The scans were recor-
ded at a heating rate of 5 ꢀC minꢁ1. Tg values are indicated. Note the
Glass 1 shows a glass transition temperature (Tg) of 58 ꢀC as
measured by Differential Scanning Calorimetry (DSC) with no absence of crystallization in both cases.
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N,N-carbonyldiimidazole (CDI), then the crude intermediate
was reacted with glass 1 to afford pure DR1 mexylaminotriazine
adduct 2 in 94% yield aer an acidic washing which removes
unreacted glass 1, DR1 and imidazole, as shown in Scheme 2.
However, attempts to rst react amine 1 with CDI followed by
DR1 resulted in the formation of an insoluble precipitate which
could not be identied. As expected, azo dye 2 readily forms
ꢀ
glasses with a Tg of 71 C (as measured by DSC with a heating
rate of 5 ꢀC minꢁ1) and does not recrystalꢁli1ze upon heating, even
ꢀ
with a heating rate as low as 0.5 C min
.
A DSC scan of glass-forming dye 2 is shown in Fig. 1b. As
expected, the mexylaminotriazine moiety imparted its ability to
promote glass formation to the Disperse Red 1 dye, without
perturbing the chromophore, as evidenced by the absorption
spectra of dye 2 in CH2Cl2 solution, shown in Fig. 2a along with
the spectra of Disperse Red 1 itself and DR1–PMMA. The
absorption of glass 2 in the visible range overlaps almost
perfectly that of DR1 (lmax ¼ 485 nm), whereas the absorption
maximum of DR1–PMMA is slightly shied (lmax ¼ 473 nm).
Thin lm deposition
Thin lms of both DR1–PMMA and DR1–glass 2 were prepared
by spin-coating from 3 wt% solutions in CH2Cl2 on thick BK7
glass substrates followed by drying in an oven. The solid lms
yielded thicknesses around 450 nm. The amorphous nature of
the lm was conrmed with powder X-ray diffraction (PXRD) by
the absence of any crystalline peaks as shown in Fig. 3. The
PXRD pattern of a sample of compound 2 is also shown and also
shows a broad halo, conrming the propensity of the material
to adopt a glassy state. It should be noted that DR1–glass
2 dissolved quicker in CH2Cl2 and formed more uniform and
higher-quality thin lms than its polymer counterpart. DR1–
PMMA is known to behave differently from one sample to the
Fig. 2 Absorbance spectra: (a) Disperse Red 1, DR1–glass 2, and DR1–
PMMA in CH2Cl2 solution; and (b) thin solid films of DR1–glass 2 and
DR1–PMMA. The spectra in CH2Cl2 solution were recorded using
concentrations of 0.01 mM for DR1 and compound 2, and 0.0006 wt%
for DR1–PMMA.
Scheme 2 Synthesis of DR1–glass 2.
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Fig. 3 Powder X-ray Diffraction (PXRD) pattern of a film and a powder
sample of DR1–glass 2. The diffraction pattern of the substrate is
shown for comparison.
other depending on chain lengths, which affects thin lm
formation. This behavior was not observed in lms of DR1–
glass 2 because of its monodisperse nature. Absorbance spectra
of these lms are reported in Fig. 2b, from which it can be
observed that even in the solid state, the DR1–glass 2 (lmax
476 nm) mirrors more closely the absorption maximum of DR1
¼
than DR1–PMMA (lmax ¼ 462 nm).
SRG inscription
A circularly polarized 532 nm diode-pumped laser was colli-
mated and incident on a Lloyd mirror where a thin lm of either
DR1–PMMA or DR1–glass 2 was placed orthogonally to the
mirror. The centre of the beam was at the junction of the sample
and the mirror, so that half of the beam was immediately
incident onto the sample, while the other half was reected
onto the sample, creating an interference pattern on the sam-
ple's surface, as previously detailed in the literature.35 This
interference pattern yielded the formation of Surface Relief
Gratings (SRG). The grating pitch could be varied by rotating the
Lloyd mirror with respect to the writing beam, but for this series
of experiments, the pitch was kept constant at 600 nm for all
SRG. The depth of the gratings was dependent on the laser
exposure time. Fig. 4 shows Atomic Force Microscopy (AFM)
scans of SRG on thin lms of DR1–PMMA and DR1–glass 2 with
laser exposure times of 300 s and 500 s, respectively.
Fig. 4 AFM scans of surface relief gratings written on thin films of (a)
DR1–PMMA polymer, and (b) DR1–glass 2, both with a 600 nm pitch.
Monitoring of diffraction efficiency via probe laser
The time-dependent diffraction efficiency was monitored for
both DR1–PMMA and DR1–glass 2 during laser irradiation. To
accomplish this, a probe He–Ne laser was incident on the
portion of the thin lm where the SRG is being inscribed, as
illustrated in Fig. 5. As the grating appeared, the rst order
Fig. 5 Experimental set-up for monitoring diffraction efficiency.
The writing laser's irradiance was varied between 50, 83 and
diffracted beam from the He–Ne laser was mechanically chop- 330 mW cmꢁ2, as the diffraction efficiency was monitored. As
ped and then incident on a silicon photodetector. The signal of seen in Fig. 6, a diffraction signal appeared almost immediately
the photodetector was then measured by a lock-in amplier and aer laser illumination in both DR1–glass 2 and DR1–PMMA.
recorded by a computer. The diffraction efficiency was obtained This is due to the formation of birefringence volume gratings
by dividing the signal of the rst by the zeroth diffraction order. within the lms. Usually, these birefringence gratings appear
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Fig. 6 Diffraction efficiency as a function of irradiation time for DR1–
PMMA and DR1–glass 2 at various laser irradiances.
Fig. 7 SRG height as a function of irradiation time for DR1–glass 2.
quicker than SRG, but are much less stable and produce less
overall diffraction. As exposure time increased, the diffraction
signal from the birefringence gratings became overshadowed by
that of the more stable SRG. Regardless, the respective diffrac-
tion efficiencies of DR1–glass 2 and DR1–PMMA were almost
identical for all irradiances used. Moreover, the rates of growth
observed for both DR1–glass 2 and DR1–PMMA were signi-
cantly faster than those observed for other azobenzene-con-
taining glasses previously published in the literature,21–26
though it is unclear whether this is the result of the experi-
mental setup, or the use in other cases of slightly different
chromophores. SRG written on lms of both DR1–PMMA and
DR1–glass 2 achieve maximum diffraction efficiency at around
gratings were placed on a temperature-regulated hot-plate and
heated from room temperature up to around 115 ꢀC with a
heating rate of around 10 ꢀC minꢁ1. The diffraction intensity of
the rst diffracted order was measured in reection using a
chopper, photodetector and a lock-in amplier. As seen in
Fig. 8, a sharp decrease in the diffraction signal occurs at 102 ꢀC
ꢀ
and 105 C for DR1–glass 2 and DR1–PMMA respectively. The
sinusoidal undulations in the diffraction signal are due to the
thermal expansion of the BK7 glass substrate as it is being
heated. The temperatures at which the SRG are erased for both
DR1–PMMA and DR1–glass 2 are very similar, and cannot be
directly rationalized by the respective Tg of both materials (the
ꢀ
Tg of the DR1–PMMA sample used was measured to be 91 C),
44% within 150–200 seconds at an irradiation of 330 mW cmꢁ2
.
ꢀ
which differs by 20 C. Two likely explanations for this obser-
Longer exposure times at this irradiation level yielded grating
degradation. Using lower irradiance values of the writing laser
only delayed the grating formation until the same diffraction
maximum was achieved. Nonetheless, more information can be
deduced from the rate of growth at lower irradiance values. For
instance, at 50 mW cmꢁ2, aer only 10–15 seconds, the
diffraction efficiency increased quickly to achieve approximately
10% efficiency, then the rate of growth decreased. This is also
evident at 83 mW cmꢁ2, but the initial quick growth plateaus at
around 12% efficiency.
vation are that either (1) the DR1 moieties start undergoing
rapid uncontrolled thermal cis–trans isomerisation, or (2) DR1–
glass 2, being capable of forming hydrogen bonds in the solid
state, even above Tg, shows hindered molecular mobility relative
to DR1–PMMA, which leads to slower kinetics of SRG degra-
dation. Further studies are currently underway to determine the
origin of these observations, which will allow gaining further
insight into the mechanisms of SRG writing and erasure.
Monitoring surface relief grating growth via AFM
The SRG height for DR1–glass 2 samples was measured using
AFM as a function of laser irradiation time at 50 mW cmꢁ2, as
shown in Fig. 7. To reduce uncertainty, each data point in Fig. 7
corresponds to the average of three AFM scans on different
locations for each SRG. These results conrm the SRG growth
rates shown in Fig. 6 since a similar correlation is observed
between the diffraction efficiency and SRG height as a function
of laser irradiation time, only aer the initial burst in the
diffraction signal caused by the birefringence volume gratings.
Temperature effects on the diffraction efficiency
Next, the temperature stability of the SRG on both DR1–PMMA
Fig. 8 Diffraction intensity as a function of temperature for DR1–
and DR1–glass 2 was investigated. Samples with surface relief PMMA and DR1–glass 2.
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Conclusions
A novel material incorporating the Disperse Red 1 chromophore
and capable of forming stable glassy phases, DR1–glass, was
synthesized using a glass-forming precursor. The synthetic
procedure used is extremely appealing because it is facile, robust,
cost-effective, high-yielding, and the product can be easily puri-
ed. The optical properties of the DR1 chromophore are not
perturbed by the glass moiety, and the material can easily be
processed from solution into high-quality thin lms. SRGs can be
readily inscribed onto the surface of thin lms of DR1–glass, and
its photophysical behavior was found to closely mirror that of
polymer-supported DR1. As polymers functionalized with DR1
units are used extensively for both their photomechanical and
non-linear optic properties, DR1–glass constitutes an extremely
exciting new material that shares the photophysical properties of
DR1, the thin lm- and glass-forming properties of polymers, and
the monodisperse, well-dened nature of small molecules.
Moreover, the synthetic strategy used herein proved highly effi-
cient, and shows promise for the design and synthesis of
molecular glasses incorporating other functional materials.
Future work will consist in developing azo-glasses featuring
extended spectral sensitivities: red-shied absorptions that
would increase the spectral range of the SRG formation process,
as well as blue shied absorptions that would increase both the
transparency range of the SRGs and their stability under ordinary
light. Another possibility offered by the ease of functionalization
of these glass-forming compounds is to develop multifunctional
materials combining opto-electronic functions with the SRGs.
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Acknowledgements
The authors would like to thank the Academic Research Pro-
gramme (ARP) of RMC and the Discovery Grants Program from
the Natural Sciences and Engineering Research Council (NSERC
#327116) for funding. The authors would also like to thank Dr
´
´
Rene Gagnon (Universite de Sherbrooke) and Dr Yimin She
(Queen's University) for mass spectrometry analyses, Robert
Whitehead (RMC) for PXRD acquisition, as well as Dr Paul
Rochon (Royal Military College of Canada) for useful discussions.
`
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