E. Ishow et al.
flow at a scan rate of 208Cminꢀ1 over the temperature range 30–2508C.
Spectroscopic grade toluene was used for spectroscopic measurements.
All air-sensitive reactions were performed under argon using a vacuum
line. The synthesis of compounds 1–8,[63] 9,[60] 10,[42] fluo2-SP,[60] 12,[40] azo-
SP,[60] and azo-SP-fluo2[60] has been reported elsewhere. Spectroscopic
grade solvents have systematically been used for steady-state and time-
resolved photophysics.
mount to that of the triptycenyl group, which has been
largely used to create nanoporosity in thin films for en-
hanced diffusion of analytes, or facilitate film stretchabili-
ty.[62] In this way, we have previously demonstrated for the
first time that fluorescent gratings could be obtained that
show a 102 emission contrast between the troughs and the
crests on account of differential accumulation and migration
of the azo compound azo-SP-fluo2 and the simultaneous
drag of the covalently linked fluorophore.
Synthesis of 4-{4-[bis(4’-tert-butylbiphenyl-4-yl)amino]phenylazo}benzoic
acid (13): A solution of Oxone (89.8 g, 146 mmol, 2 equiv) in water
(450 mL) was added to
a solution of 4-aminobenzoic acid (9.99 g,
72.8 mmol, 1 equiv) in dichloromethane (110 mL). The solution was
stirred under argon at room temperature for 1 h. The precipitate was col-
lected under vacuum, washed with water, and dried under vacuum over
solid phosphorus pentoxide to yield quantitatively a crude yellow solid
used with no further purification. 4-Nitrosobenzoic acid (570 mg,
3.82 mmol, 2 equiv) was dissolved in a mixture of DMSO/glacial acetic
acid (1:1; 52 mL) under argon. Bis(4’-tert-butylbiphenyl-4-yl)-4-amino-
phenylamine 12 (1.0 g, 1.91 mmol, 1 equiv) was added portionwise, mean-
while the pale yellow solution turned deep brown-red. After stirring for
48 h at room temperature, a fine red product formed, which correspond-
ed to the pure compound 13. This was filtered off and washed well with
water (1.2 mg, 95%). 1H NMR (400 MHz, CDCl3, TMS): d=8.22 (d, 3J-
Conclusion
In the search for photochromic azo molecular materials to
form fluorescent patterns upon illumination, fluorescent
units known to emit light in the solid state have been at-
tached to azo moieties. Strong dependence of the fluores-
cence properties on the linker structure has been found,
thereby prompting us to perform comparative measure-
ments by using steady-state and time-resolved fluorescence,
and femtosecond transient absorption spectroscopy in tolu-
ene solution, which mimics well the solid state. The photoi-
somerization quantum yields FEZ (ꢄ0.15–0.35) and FZE
A
R
ACHTUNGTRENNUNG(H,H)=
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
ꢀ
AHCTUNGTREG(NNUN H,H)=8.7 Hz, 2H), 1.37 ppm (s, 18H; tBu); HRMS (MALDI-
TOF): m/z calcd for C45H43N3O2 [M+]: 657.3355; found: 657.33498.
Synthesis of methyl 4-{4-[bis(4’-tert-butylbiphenyl-4-yl)amino]phenylazo}-
benzoate (14): SOCl2 (0.2 mL, 2.74 mmol, 6 equiv) was added to a solu-
tion of 13 (300 mg, 0.46 mmol, 1 equiv) in anhydrous dichloromethane
(10 mL) under argon. The reaction mixture was heated to reflux for 2 h.
After cooling to room temperature, the residual SOCl2 was evaporated
and the resulting acid chloride was quenched with an excess amount of
anhydrous methanol (5 mL). The solution was stirred at 408C for a fur-
ther 2 h and evaporated to dryness. After dissolution in dichloromethane,
the solution was successively washed with a saturated solution of sodium
hydrogen carbonate and water. The extracted organic layer was dried
over anhydrous sodium sulfate. Concentration under vacuum followed by
silica gel column chromatography using a 1:1 dichloromethane/petroleum
ether mixture as an eluent afforded 14 (azoE) as an orange-red glassy
solid (145 mg, 47%); Tg =688C. 1H NMR (400 MHz, CDCl3, TMS): d=
A
65%) were found to be similar for the model and bifunc-
tional molecules, thus proving the negligible electronic influ-
ence of the fluorophore on the photochromic behavior. Ki-
netic analyses of the femtosecond transient absorption spec-
tra of the model and bifunctional systems reveal that the in-
troduction of a triptycenyl-like rigid and nonconjugated
spacer between the azo and fluorescent units suppresses
competitive energy transfer from the fluorophore to the azo
moiety.
As such, both photoisomerization and fluorescence are
conserved, which allows for the creation of fluorescent pat-
terns in thin films exposed to interferential illumination.
This structuration, which relies on multiple E–Z photoiso-
merization cycles of the azo units, is highly favored by the
presence of the spacer. This creates additional free volume,
compulsory for efficient azo bulk migration. These studies
represent the first thorough examination of the photophysics
of bifunctional compounds that contain structurally distinct
push–pull fluorescent and azo units. The possibility to ad-
dress both the emissive and photoisomerization properties
at the same wavelength while recording redshifted emission
opens exciting perspectives in the field of photoinduced lo-
comotion and tracking at the single-molecule level.
3
3
3
8.16 (d, JACTHNGUTREN(NUNG H,H)=8.2 Hz, 2H), 7.90 (d, JACHTUNGTRENNUNG
(H,H)=8.2 Hz, 4H), 7.56 (d, 3J
U
ACHTUNGTRENNUNG
8.2 Hz, 4H), 7.46 (d, 3J
A
ACHTUNGTRENNUNG
3
ꢀ
4H), 7.21 (d, J
(H,H)=8.7 Hz, 2H), 3.95 (s, 3H; CO2CH3), 1.37 ppm (s,
18H; tBu); 13C NMR (75 MHz, CDCl3, TMS): d=166.8, 159.8, 155.7,
150.3, 147.3, 145.7, 137.6, 137.2, 131.1, 130.7, 128.2, 126.6, 125.95, 125.92,
124.9, 122.4, 121.6, 52.4, 34.7, 31.5 ppm; UV/Vis (toluene): lmax (e)=465
(17900), 330 nm (21100 molꢀ1dmꢀ3 cmꢀ1); HRMS (MALDI-TOF): m/z
calcd for C46H45N3O2 [M+]: 671.3512; found: 671.35063.
ꢀ
Synthesis of 5-[bis(4’-tert-butylbiphenyl-4-yl)amino]-2-nitrobenzyl 4-{4-
[bis(4’-tert-butylbiphenyl-4-yl)amino]phenylazo}benzoate (15): A solution
of acid 13 (112 mg, 0.17 mmol, 1 equiv), 4-(dimethylamino)pyridinium p-
toluenesulfonate (DPTS; 16 mg, 0.05 mmol, 0.3 equiv), diisopropylcarbo-
diimide (DIPC; 32 mg, 0.25 mmol, 1.5 equiv) in anhydrous dichlorome-
thane (12 mL) was added slowly to a solution of alcohol 7 (100 mg,
0.17 mmol, 1 equiv) in dry dichloromethane (12 mL). The reaction mix-
ture was allowed to stir at reflux overnight. Concentration under vacuum
followed by silica gel column chromatography using a dichloromethane/
petroleum ether mixture as an eluent from a 1:1 to 7:3 ratio afforded 15
(azo-fluo1) as a glassy red solid (130 mg, 60%); Tg =1698C. 1H NMR
Experimental Section
(400 MHz, CDCl3, TMS): d=8.16 (d, 3J
(H,H)=8.7 Hz, 2H), 7.86 (d, 3J(H,H)=9.2 Hz, 2H), 7.75 (d, 3J
8.7 Hz, 2H), 7.58 (d, 3J(H,H)=8.2 Hz, 4H), 7.54 (d, 3J
(H,H)=8.7 Hz,
4H), 7.53 (d, 3J(H,H)=8.2 Hz, 4H), 7.49 (d, 3J
(H,H)=8.2 Hz, 4H), 7.44
(d, 3J(H,H)=8.5 Hz, 4H), 7.39 (d, 3J(H,H)=8.5 Hz, 4H), 7.31 (d, 4J-
(H,H)=2.7 Hz, 1H), 7.28 (d, 3J(H,H)=8.7 Hz, 4H), 7.26 (d, 3J
(H,H)=
8.2 Hz, 4H), 7.22 (d, 3J(H,H)=9.2 Hz, 2H), 6.98 (dd, 3J
(H,H)=9.2 Hz,
ACHTUNGTRENNUNG
General: 1H and 13C NMR spectra were recorded using
a JEOL
A
R
ACHTUNGTRENNUNG
400 MHz spectrometer and chemical shifts were reported in ppm relative
to TMS or referenced to the residual solvent. High-resolution mass spec-
tra were obtained by MALDI-TOF (Voyager DE-STR, Applied Biosys-
tems). Melting points were measured by using a Kofler bench. Glass tran-
sition temperatures Tg were measured by using differential scanning calo-
rimetry (Perkin–Elmer Pyris Diamond) in aluminum caps under nitrogen
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
R
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
3718
ꢄ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 3706 – 3720