Triple bonds chromophores

The calix[4] pyrroles functionalized with nitrobenzenes 5 and 6 [16] can act as F" sensors. These systems bear an appended chromophore directly linked to the calix[4] pyrrole skeleton through a conjugated C=C triple bond. Upon addition of tetrabutylammonium F", solutions of 5 and 6 in CH2C12 turned from pale yellow (Amax=391 nm) to intense yellow (Amax=433 nm) for 5 and from yellow (Amax=441 nm) to red (Amax=498 nm) for 6. In addition, the color changed from yellow (Amax=441 nm) to orange when Cl" (Amax=483 nm) and H2POj (Amax-478 nm) were added to a solution of 6. 

The hb-PAEs of hb-P13 and hb-P15 contain NLO-active azo-functionalities, which are soluble, film-forming, and morphologically stable (Tg > 180 °C). Their poled films exhibited high SHG coefficients ( 33 up to 177pm/V), thanks to the chromophore-separation and site-isolation effects of the hyperbranched structures of the polymers in the three-dimensional space (Table 5) [28]. The optical nonlinearities of the poled films of the polymers are thermally stable with no drop in d33 observable when heated to 152 °C (Fig. 8), due to the facile cross-linking of the multiple acetylenic triple bonds in the hb-PAEs at moderate temperatures (e.g., 88 °C). 

The interaction between a triple bond and an aromatic ring was first studied with paracyclophynes (10) > but only ambiguous evidence was observed in their spectra . The first positive evidence for such a transannular interaction was shown in the spectra of naphthalenophapolyynes (11) . Here all the absorption bands appear at the same positions, but their intensities in the cyclic monomer 11a are markedly decreased as compared with the intensities per unit chromophore of the cyclic dimer 11b and trimer 11c. This hypochromism of 11a was explained in terms of a dispersion... 

The part of the molecule that is responsible for the absorption of light is called the chromophore (see Figure 7.4) and consists of a region of double or triple bonds, especially if the multiple bonds are conjugated, that is if the... 

D-A chromophores bearing triple bonds were investigated to understand the relationship between chromophore size and both nonlinear absorption [425] and nonlinear hyperpolarizablity [446]. In particular, 48 [425] comprises a chromophore bearing at one side a dialkylamino group as donor and at the opposite side... 

For this purpose, 62-66 are interesting TP chromophores because variation of the core in 63 and 66 and changing the nature of the conjugated connectors by replacing the double bond by a triple bond in 62 and 63 and vice versa results in a drawback about the function of double and triple bonds in such conjugated systems. In addition, incorporation of the triple bond in both 64 and 65 and comparison of data with 60 gives information about how these structural changes affect TPA. 

Large TPA was reported for the bis(pyridylstyryl)-substituted diacetylene 89 that was additionally alkylated at the pyridinium nitrogen, resulting in 90. In accordance with the charged pyridinium chromophores 53, a larger TPA was also observed for 90 in comparison with 89. This example also shows that incorporation of triple bonds into the II-bridge does not diminish TPA even in A-n-A chromophores. It confirms that the triple bond of N—Ph—C=C—Ph—C=C—Ph —N chromophores does not diminish S. 

Conjugated oligomers, which consist of CC double or triple bonds and/or 1,4-phenylene units, form rigid rods with a well defined length L. The extent of the chromophores/electrophores can be calculated by linear functions L n), where n is the number of repeat units. Scheme 11.24 gives a survey of such oligomers with k, I, m = 0,1. Many more conjugated series can be conceived with k,l,m> 1... 

A more important fact is that the chromophore is not rigidly fixed to the biopolymer and, thus, rotates about the bond finking it to the biopolymer. Consequently, the anisotropy decay kinetics is found to be double or triple exponential, due to the contributions from internal and global rotation of the macromolecule. The same concept applies for the rotational wobble of that portion of the biopolymer in proximity to the fluorophore or in the more defined case for the rotation of a molecular domain [135]. 

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