Fig. 3 Oscillation of the optical density generated by green light irradiation (lirradiation = 532 nm) (a) and photostability after 2500 laser pulses (b)
of an ethanol solution of azo-dye 10 at 298 K ([AZO] = 20 mM, lobs = 545 nm).
Taking into account the very fast thermal isomerisation
kinetics exhibited by the amino-substituted azopyridinium
salts 7, 9 and 10, they are the best candidates thus far for
light-driven real time information processing and optical
oscillating systems. Fig. 3(a) shows the oscillation of the optical
density of azo-dye 10 in ethanol solution at room temperature
with the time. The maximum oscillation frequency in the optical
properties for azocompounds 7, 9 and 10 ranges from 0.9 MHz
to 1.2 MHz at 298 K (Table 1).
atmosphere, and then, CH3I (3 cm3) was added. The solution was
stirred at room temperature for 2 hours. After, the product was
precipitated by adding hexanes, isolated by vacuum filtration and
dried. 7 was obtained as a reddish crystalline solid (160 mg, 63%).
1H NMR (400 MHz, d6-acetone) d: 9.05 (2H, d, arH, J = 7.1 Hz), 8.24
(2H, d, arH, J = 7.1 Hz), 7.93 (2H, d, arH, J = 9.0 Hz), 6.93 (2H, d,
arH, J = 9.0 Hz), 4.58 (3H, s, CH3) ppm. FT-IR (ATR) n: 3343 and
3272 (N–H st), 3170 (QC–H st), 1600 (CQC st), 1474 (NQN st)
+
cmÀ1. HR-MS (ESI-MS): m/z Calcd. for C12H13N4 [M+] 213.1135;
found 213.1140.
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Both the repeatability and photostability of our prototypes
were checked by submitting them to several pulsed green light
(532 nm)–dark cycles. Fig. 3(b) evidences the high photo-
stability exhibited by the amino-substituted azopyridinium
salt 10 in ethanol solution at 298 K thereby observing that after
2500 cycles neither the absorbance change nor the relaxation time
of the molecular oscillator was altered by the continuous work of
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and 10 in the different solvents analyzed.
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aminoazopyridinium salts reported herein make them ideal
photo-active molecules for real time information transmitting
systems and optical oscillators. In fact, the information trans-
mission capability of these azopyridinium salts elapse 105-fold
faster than that by means of the neuronal synapses (0.5 ms to
10 ms). The oscillation frequency of the systems reported herein
is around 1 MHz at room temperature and they show no fatigue
upon continuous work. On the other hand, their high solubility
in aqueous media makes them valuable chromophores for
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Financial support for this research was obtained from the
Ministerio de Ciencia e Innovacion (Spain) through grant no.
´
CTQ2009-13797.
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Notes and references
w Synthesis of 4-[(4-aminophenyl)azo]-1-methylpyridinium iodide (7):
2 (150 mg) was dissolved in anhydrous CH2Cl2 (10 cm3) under an inert
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c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 3421–3423 3423