Simple Chromophores

Some of the simple chromophoric groups, together with the absorption maxima of simple compounds containing these groups, are collected in... 

Reaction with vatious nucleophilic reagents provides several types of dyes. Those with simple chromophores include the hernicyanine iodide [16384-23-9] (20) in which one of the terminal nitrogens is nonheterocyclic enamine triearbocyanine iodide [16384-24-0] (21) useful as a laser dye and the merocyanine [32634-47-2] (22). More complex polynuclear dyes from reagents with more than one reactive site include the trinuclear BAB (Basic-Acidic-Basic) dye [66037-42-1] (23) containing basic-acidic-basic heterocycles. Indolizinium quaternary salts (24), derived from reaction of diphenylcyclopropenone [886-38-4] and 4-picoline [108-89-4] provide trimethine dyes such as (25), which absorb near 950 nm in the infrared (23). 

The effect of conjugation on the UV-Vis spectrum of a simple chromophore is shown in Table 2.2, in which we can see that the conjugated MVK has an increased Amax and for both absorption bands. 

Table 7.3 lists typical absorptions of simple isolated chromophores. You may notice that these simple chromophores nearly all absorb at approximately the same wavelength (160 to 210 nm). 

This simple orbital model in Figure 12.25 is not entirely consistent with the available experimental data. Indeed, Kropp called the isolated carbon-carbon double bond "one of the most deceptively simple chromophores available to the organic chemist." ° Even though the end absorption apparently includes the n,ii transition, there is evidence that there may also be weak absorption due to tc —> c and Rydberg transitions. In alkenes, the Rydberg state is thought to result from promotion of an electron from the n orbital to a carbon orbital that has the characteristics of a 3s orbital in helium. 

The similarities in chemical behaviour across the lanthanides mean that kinetically stable lanthanide complexes offer a degree of control that cannot readily be achieved through selective self-assembly of small building blocks. Azamacrocycle complexes derived from cyclen amino-carboxylates are particularly suited to this, and ternary complexes can be used to study the photophysical behaviour of lanthanide complexes. We initially used such an approach to probe the effectiveness of chromophores as sensitizers for lanthanides without recourse to extensive synthesis (as illustrated in Fig. 7). This approach can be used with simple chromophores to probe the mechanism of energy transfer. For instance, tetrathiafulvalene... 

For this relatively simple chromophore which, as compared with DANS, is two atoms shorter and is bent, a Po three times higher was measured [15]. 

There are a large variety of partially empirical methods for the determination of the absolute configuration of simple chromophores. The best known (and most reliable) sector rule is the octant rule for the carbonyl chromophore. While all sector rules have a theoretical foundation based on the character of the states involved in the transition" and may be supported by theoretical computations, focus is directed here to methods which have computer implementations. 

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