**1. Introduction**

316 Macro to Nano Spectroscopy

Valderrama, P., & Poppi R.J., (2009). Second Order Standard Addition Method and

160-165.

Fluorescence Spectroscopy in the Quantification of Ibuprofen Enantiomers in Biological Fluids, *Chemometrics and Intelligent Laboratory Systems*, Vol.106, No.2, pp.

> The properties of colligative states of spontaneously aggregated polymethine dyes differ substantially from those of monomeric dye. Excellent examples of such self-organized molecular ensembles are J-aggregates of cyanine dyes. The J-aggregated state is now being considered for a number of non-cyanine dyes, the cyanine dye is still the most known and effective dye for J-aggregate formation (Wurthner, 2011). J-aggregates of cyanine dyes, first discovered by Jelley and Scheibe in 1936 (Jelley, 1936; Scheibe, 1936), have been studied for many years (Kobayashi, 1996). J-aggregates of cyanine dyes attract the attention of the researchers due to their interesting optical properties. J-aggregates are characterized by a strong absorption peak (J-peak) with narrow line widths which are bathochromically shifted relative to the absorption band of the monomeric dye. Their role as photographic sensitizers can hardly be overestimated (Tani, 1996; Trosken et al., 1995; Shapiro, 1994). Aggregates of dye molecules may be used to mimic light harvesting arrays and to prepare artificial photosynthetic systems (McDermott et al., 1995; Blankenship, 1995). Another development is the efficient electroluminescence revealed in single-layer light-emitting diodes based on electron-hole conducting polymers containing nano-crystalline phases of J-aggregates of cyanine dyes (Mal'tsev et al., 1999).

> The promise in the property of J-aggregates lies in their high non-linear cubic optical susceptibility, χ(3) ~ 10-7 esu, with a fast response time at the J-peak resonance in solutions and polymer films (Wang, 1991; Bogdanov et al., 1991).

> The pseudoisocyanine dye (PIC) is the known dye which forms the J-aggregates in solutions. Of particular interest is the formation and non-linear optical properties of Jaggregates in thin solid films. Films of J-aggregates of organic dyes are promising nanomaterials for non-linear optical switches because they have the unique properties of high non-linear bleaching and non-linear refraction (Markov et al., 2000). As shown in Glaeske et al. (2001), films of J-aggregates with bistable behaviour may be the basis for twodimensional optical switches, controllable by light. The non-linear optical properties of

Optical and Resonant Non-Linear Optical Properties

R6G laser pumped using 5 ns pulsed Nd:YAG laser.

IF C

shift, ANF– adjusted neutral filter, PD–photodiode.

Nd-YAG+SHG DL

calibration was carried out with etalon CS2 substance (

were calculated by equations:

where, c – light velocity in vacuum,

multiplier.

of J-Aggregates of Pseudoisocyanine Derivatives in Thin Solid Films 319

The steady-state luminescence spectra were recorded on the Cary-Eclipse (Varian) and Hitachi 850 spectrofluorimeters. The kinetics of the luminescence decay was measured on the set-up of the Federal Institute for Materials Research and Testing (Berlin, Germany) with the assistance of researcher Ch. Spitz. The excitation was carried out in the cryostat by the pulse irradiation of the dye laser (R6G dye) with pulse duration 80ps synchronously pumped by pulse mode-locking Ar+ laser. The luminescence of the PIC J-aggregates was separated by monochromator and measured in the photon counting regime by the photo-

The measurement of non-linear cubic susceptibilities of J-aggregates' PIC in thin solid films was carried out using the Z-scan method on the set-up shown on fig. 1 based on the dye

ANF

L5 sample

Fig. 1. Z-scan set-up. Nd-YAG+SHG – pulse laser, DL – Dye laser, L1-L4 –lenses, А – Aperture diaphragm, P – Glan prism, IF – interference filter, C– compensator of the beam

P

The weak luminescence of the laser dye was cut off by the interference filter IF590 (Carl Zeiss Jena). The light signals were measured by photodiodes and the measured T(z) curves had 200 experimental points with the average value taken from the tens pulses. The

of the real *Re(3)* and imaginary *Im(3)* parts of the cubic susceptibility in the esu units from the

 

 2 2 (3) 0 0 2

Im ( ) <sup>640</sup> *cn*

 2 (3) 0 0 3

Re ( ) <sup>160</sup> <sup>4</sup>

*cn*

measured values' non-linear refraction coefficient *γ* and absorption coefficient

L2 L3

 

0

*n*

 

 *-* irradiation wavelength.

 

0

*n*

=(3.6+0.3)10-14 cm2/W). The values

L4

PD

PD

(1)

(2)

in SI units

organic dye J-aggregates have been intensively studied for application in future optical telecommunication and signal processing systems with ultrahigh bit rates (Tbit/s) (Furuki et al., 2000). The observed giant resonant third-order susceptibility in PIC thin solid films ~10-5-10-4 esu (5 orders of magnitude greater than in polyconjugated polymers) and accessible production of optical quality films over a large area gives the possibility of Jaggregates application in telecommunication for terahertz demultiplexing of optical signals.

The methods for obtaining the J-aggregates in solutions do not give stable aggregates, which hampers their application as non-linear optical materials. Besides, a thin film geometry is preferable for applications. Therefore, the preparation of large area thin films of J-aggregates with thermal and photochemical stability, and high optical quality is vital for practical application and a matter of much current interest. The pseudoisocyanine at proper conditions efficiently forms J-aggregates in solid thin films (Shelkovnikov et al., 2002). The aim of this paper is to clarify the influence on the spectral linear and non-linear properties of PIC J-aggregates in thin solid films using a number of factors: structure of pseudoisocyanine dye derivatives, local field factor and character of J-peak broadening.
