Chromophore density

Their ability to achieve a high chromophore density (for example, it is possible to introduce three conjugated chains about a single N-atom core in contrast to the two more normally possible with a linear macromolecule) [84]... 

In Fig. 3, the values for the electron-number-related static hyperpolarizability fiJN312 obtained for these ionic chromophores (open symbols) have been compared with the same values for the best dipolar, neutral chromophores reported so far (diamonds).31 32 These chromophores, with a reduced number of electrons N equal to 20, have dynamic first hyperpolarizabilities approaching 3000 x 10 30 esu at a fundamental wavelength of 1.064 pm, in combination with a charge transfer (CT) absorption band around 650 nm. It is clear that at this point, the neutral NLOphores surpass the available ionic stilbazolium chromophores for second-order NLO applications, however, only at the molecular level. The chromophore number density that can be achieved in ionic crystals is larger than the optimal chromophore density in guest-host systems. 

For both PI-1 and PX-2, assuming that n e (n, mean refractive index) for optical frequencies, the mean dielectric constant, (e) decreases upon irradiation (A pi = - 0.023, A pi 2 - - 0.016). The dielectric constant is proportional to the chromophore density and the decrease upon irradiation suggests a quasi-... 

Fig. 21 Theoretical chromophore absorption model to analyze the dynamic absorption of the triazene polymer. Initially the polymer chromphores are in the ground state with the chromophore density p. Absorption of photons from the laser pulse promotes some chromophores to the first and second excited states. The absorption cross section of both are indicated with G and a2. REPRINTED WITH PERMISSION OF [Ref. 60], COPYRIGHT (1996) Springer Verlag...

In the absorption spectra for TP1 (X = 0, R - (CH2)6, R2 = CH3) as shown in Fig. 14.13, two distinct absorption maxima can be distinguished. The Rj and R2 substitutes change the properties such as Tg, film forming, and chromophore density. One maximum around 200 nm, which can be assigned to the aromatic system, and the other maximum around 330 nm that corresponds to the triazene unit [135]. These two well-separated absorption regions allow an excitation of different chromophores with different irradiation wavelengths such as 193, 248, and 308 nm and thereby to study their influence on the ablation behavior. 

To enhance the chromophore density and to obtain stable film.s, polyglutamates that have azobenzene moieties in every side chain have been synthesized (38, 39). In this case, the side chains have to be tailored to keep the hairy rod character of the polymer. The length of the alkyl spacer between the chromophore and the polymer backbone (n = 2, 3, 4, 6), as well as the length and means of tethering of the alkyl tail to the chromophore, have to be adjusted or -OC10H21) so that the side chain region is in a... 

The ASE process occurs in a gain medium whenever the optical confinement is superior, or the decoherence time is short (Section 22.2). The confinement can be described by the radiation leakage rate k, whereas the cooperation among chromophores may be quantified by the Arrechi-Courtens time [112] Tc, which is inversely proportional to the chromophore density in the medium. The value of (kTc) accounts for the relative number of photons emitted by the ASE process [96]. This happens in both polymer solutions (in a cuvette), or in neat polymer films of thickness 100 nm deposited on glass substrates due to optical confinement formed by the film waveguiding properties. 

Fig. 3. (a) An early version multichromophore dendrimer (105) is shown. This cross-linkable dendrimer yields an electrooptic coefficient of 60 pnW at 1.55 /xm wavelength that is stable under testing at 85°C for 1000 h. (b) Schematic representation. = 4664 Chromophore density 33 wt%. 

One unique feature of mainchain chromophoric polymers is that the dipoles or chromophores are direcdy bonded to one another. This means that it may be possible to get enhanced second-order NLO properties, and because the chromophores are in the polymer mainchain, it should be much more difficult for the chromophores to relax, which should increase the stability of the second-order NLO properties. Another advantage is that every polymer repeat unit has a chromophore, therefore the chromophore density is high (25 x 10 chromophores/cm ) in the case of poly((4-N-ethylene-N-ethylamino)-a-cyanocinnamate). ... 

The work of GAF and LAF shows that the strong distance dependence of the microscopic transfer rate will yield a collective or macroscopic rate of EET that is very sensitive to chromophore density, and to fluctuations in chromophore density. It is this feature of collective EET that has initiated the present investigation of EET as a probe of macromolecular structure. When chromophores are attached to polymer chains in a well defined manner, the EET dynamics will reflect ensemble averaged properties such as local chain segment density and flexibility, global configurational statistics, and intramolecular dimensions. 

---