Chromophore, defined

This work shows that the overall spectra obtained by Hsia Graham, by Rushton, et. al. and by Wald are all reproducible using the chromophores defined in this work and the logarithmic summation process at the heart of the perception of luminance (See Sections 16.3 17.2). Contrary to the widely reproduced proposition by Wald, the three chromophores exhibit peak absorptions near 437, 532 and 625 nm. 

The relationship between the structure of a polymer chain and it dynamics has long been a focus for work in polymer science. It is on the local level that the dynamics of a polymer chain are most directly linked to the monomer structure. The techniques of time-resolved optical spectroscopy provide a uniquely detailed picture of local segmental motions. This is accomplished through the direct observation of the time dependence of the orientation autocorrelation function of a bond in the polymer chain. Optical techniques include fluorescence anisotropy decay experiments (J ) and transient absorption measurements(7 ). A common feature of these methods is the use of polymer chains with chromophore labels attached. The transition dipole of the attached chromophore defines the vector whose reorientation is observed in the experiment. A common labeling scheme is to bond the chromophore into the polymer chain such that the transition dipole is rigidly affixed either para 1 lei (1-7) or perpendicular(8,9) to the chain backbone. 

The first study in which a full CASSCE treatment was used for the non-adiabatic dynamics of a polyatomic system was a study on a model of the retinal chromophore [86]. The cis-trans photoisomerization of retinal is the primary event in vision, but despite much study the mechanism for this process is still unclear. The minimal model for retinal is l-cis-CjH NHj, which had been studied in an earlier quantum chemisti7 study [230]. There, it had been established that a conical intersection exists between the Si and So states with the cis-trans defining torsion angle at approximately a = 80° (cis is at 0°). Two... 

The state of research on the two classes of acetylenic compounds described in this article, the cyclo[ ]carbons and tetraethynylethene derivatives, differs drastically. The synthesis of bulk quantities of a cyclocarbon remains a fascinating challenge in view of the expected instability of these compounds. These compounds would represent a fourth allotropic form of carbon, in addition to diamond, graphite, and the fullerenes. The full spectral characterization of macroscopic quantities of cyclo-C should provide a unique experimental calibration for the power of theoretical predictions dealing with the electronic and structural properties of conjugated n-chromophores of substantial size and number of heavy atoms. We believe that access to bulk cyclocarbon quantities will eventually be accomplished by controlled thermal or photochemical cycloreversion reactions of structurally defined, stable precursor molecules similar to those described in this review. 

Macrocyclic receptors made up of two, four or six zinc porphyrins covalently connected have been used as hosts for di- and tetrapyridyl porphyrins, and the association constants are in the range 105-106 M-1, reflecting the cooperative multipoint interactions (84-86). These host-guest complexes have well-defined structures, like Lindsey s wheel and spoke architecture (70, Fig. 27a), and have been used to study energy and electron transfer between the chromophores. A similar host-guest complex (71, Fig. 27b) was reported by Slone and Hupp (87), but in this case the host was itself a supramolecular structure. Four 5,15-dipyridyl zinc porphyrins coordinated to four rhenium complexes form the walls of a macrocyclic molecular square. This host binds meso-tetrapyridyl and 5,15-dipyridyl porphyrins with association constants of 4 x 107 M-1 and 3 x 106 M-1 respectively. 

Model analogs of the green type chromophore HBI have been chemically synthe-tized in different forms carrying blocking groups in place of the protein polypeptide chain [21, 24, 68, 69]. However, the covalent structure of HBI does not uniquely define its optical properties, because the molecule undergoes several protonation and conformational equilibria that directly affect its electronic structure. 

Metal phthalocyanines functionalized with four helicenes (62) have also been reported to form chiral columnar aggregates.76 In chloroform solutions of these metal phthalocyanines aggregation into columns occurred upon addition of ethanol, as was observed by UV-Vis spectroscopy. CD spectroscopy revealed that the chromophores within the columnar aggregates are in a chiral environment, implying that the chirality of the peripheral helicenes has been transferred to the supramolecular aggregates. These phthalocyanines stack with a typical intermolecular distance of 3.4 A, and calculations have indicated that to allow this distance the two phthalocyanine moieties have to be rotated because of the bulkiness of the helicenes. It can easily be imagined that a phthalocyanine provided with both R and S helicenes cannot stack in such a defined manner because of the steric interactions between the nonconform helicenes. 

For a system containing two chromophores i and j, the exciton chirality (positive or negative) governing the sign and amplitude of the split Cotton effect can be theoretically defined as below59 ... 

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