1. Photoacoustic Monitoring of the
Macroscopic Orientational Order in
Disperse Red 1 Azo-Dye Based
Dissolutions
Vicente Torres, R. Castañeda-
Guzmán, & O.G. Morales-Saavedra.
CCADET-UNAM (Mexico)
1

2. 2
Outline of the talk
• Introduction
– Molecular structure of the sample
– UV-Vis spectra of dissolution and glass-cell
• Experimental details
– Experimental set-up http://digital.library.cornell.edu/
• Results and discussions
– Graph: averaged photoacoustic signals
– Graph: Amplitude Fourier analysis
– Graph: Correlation analysis
– Graph: RMS-amplitude, and optical transmission
vs. Voltage steps
– Agreement with other investigations
– Important parameters
• Main conclusions and work to the future

3. 3
Objetives:
• Suggest a new photoacoustic methodology to
characterize anisotropy in rod-like organic
materials
• Perform the PA study in switchable (poled and
unpoled ) phases in memory-less samples

4. 4
Poled organic structures are inportant in:
• Organic (dye) Solar Cells
• (Organic Light Emitters
Diode) OLEDs
• Organic Non-linear Optics:
Second Harmonic
Generation (SHG)

5. 5
Chemical structure of the Disperse-Red-1
(DR1).
• This standard NLO dye consists of (a) electron
donor and (c) acceptor groups situated at two
ends of a (b) azo-bridge (p-conjugated chain).
1) No chemical degradation for laser
action
2) No structure bends in the DR1
3) No electrical/orientational memory
effects
DR1/Toluene = 0.175 mg/mL

6. 6
Comparative UV–Vis absorbance spectra
Only the cromophore DR1 exhibits a strong and
characteristic absorbance band within the visible
range, near to lex = 532 nm laser excitation.
0.087 mg/mL
H/E2k
a

7. 7
Experimental set-up
• Homemade electro-optical glass-cell (GC): ITO/glass,
2x0.2x1 cm3
• 0-6.1 KV, 5 min/voltage-step @ 25oC. 200 samples

8. 8
Experimental set-up (Detail)
Glass cell with
Pin DR1/Toluene dissolution
Sin
To the optical
PZT-Sensor Sensor

9. 9
Averaged PLPA-signals for the DR1/toluene
dissolution.

10. 10
Relative amplitude Fourier-analysis

11. 11
Correlation analyses vs. Voltage

12. 12
RMS-amplitude, and optical transmission
vs. Applied voltage

13. 13
Simple model (unpoled phase)
• Acoustics: DR1 as
line of
transmission
(wire-can model )
• Optics: DR1 as a
dipolar antenna

14. 14
Simple model (poled phase)
CPLPA ~ 8.1%, Copt ~ 33.3%

15. 15
In the literature: Dicroic polarizer case
CPLPA ~ 43%, Copt ~ 67%
Laser Linear
beam Polarizer
PZT
sensor
Torres-Zúñiga, V., et. al., Optical absorption
photoacoustic measurements for determination
of molecular symmetries in a dichroic organic-
film, Optics Express 16(25), pp. 20724-20733
(2008).

16. 16
In the literature: Poled film case
CPLPA ~ 3%
Torres-Zúñiga, V., et.al., Monitoring molecular orientational order in NLO pushpull based
polymeric films via photoacoustic measurements, Opt. and Lasers in Engineering 49(12),
pp. 1413-1421 (2011).

17. 17
Anisotropy (A) and Macroscopic
Orientational Order (f)
APLPA ~ 5.6 %, Aopt ~ 21.4%
fPLPA ~ 10%, fopt ~ 45%

18. 18
Main conclusions and work to the future
1) The implemented experimental set-up is versatile and easy to
assemble. Then, in future works is possible perform variations in the
microphone position and use other polar molecules.
2) The DR1 molecule is a good option to implement PA experiments
@532 nm. However, in future works will be optimum obtain PA signals
derived from the resonance optical peak interaction.
3) Intense PA signals were obtained from the induced arrangement in the
DR1 dissolutions. The PA signals are suitable to perform different
numerical analysis based on the amplitude, the frequency or the
phase.
4) All the PA and optical analysis evidence (without contradictions) the
change from an isotropic phase to an anisotropic one caused by the
electric field. In particular: APLPA ~5.6%, and fPLPA ~10%.

19. 19
Thank you for your attention!
• Any question?
• Email: vicentz@gmail.com