Chromophore absorption

Iwase Y, Kamada K, Ohta K, Kondo K (2003) Synthesis and photophysical properties of new two-photon absorption chromophores containing a diacetylene moiety as the central tt-bridge. Mater J Chem 13 1575-1581... 

When the synthetic procedure to prepare Pt2(P20sH2)4- (equation 441) is carried out at higher temperature, a higher oligomeric complex with platinum(U) centers coupled by an oligomeric condensed phosphorous acid ligand is formed. Little information is known about the complex except that the intense absorption chromophore is now at 580 nm and the emission in the red at 650 nm.1501... 

Based on the expression for, a large increase in the useful NLO coefficient for a fixed wavelength is predicted in the case where the absorbance of the NLO dye lies between the fundamental and second harmonic. Residual absorption at the second harmonic is the limiting factor in the practical application of this technique, and has been addressed through the synthesis of new dyes. Improvement of lOx in reducing this absorbance has been achieved, and another factor of 5-lOx is estimated to be required before practical devices can be fabricated. Franck-Condon effects (vibronic structure) appear to be responsible for this residual absorption because small, rigid chromophores are often correlated with the lowest amounts of absorption. Chromophores based loosely on... 

Zeng Z, Guan Z, Xu QH, Wu J (2011) Octupolar polycyclic aromatic hydrocarbons as new two-photon absorption chromophores synthesis and application for optical power limiting. Chem Eur J 17 3837-3841... 

Absorption Chromophoric groups AZ, A may Conjugated polymers Hydrogels containing indicator dyes... 

FDCD measurements have the potential for providing valuable spectroscopic and structural information for systems in which conventional CD measurements are problematic. Of particular interest are complex systems containing multiple absorption chromophores but only one fluorescent chromophore. It is also possible to use the intrinsically higher sensitivity of luminescence detection to determine... 

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

When two or more chromophores are present in the same molecule, their absorption is usually additive as long as they are separated by two or more single bonds. Two chromophores in conjugation (i.e., separated by only one single bond) give rise to a new tjrpe of absorption with increased Some examples are given in Table IX. 

Most of the qualitative relationships between color and structure of methine dyes based on the resonance theory were established independently during the 1940 s by Brooker and coworkers (16, 72-74) and by Kiprianov (75-78), and specific application to thiazolo dyes appeared later with the studies of Knott (79) and Rout (80-84). In this approach, the absorptions of dyes belonging to amidinium ionic system are conveyed by a group of contributing structures resulting from the different ways of localization of the 2n rr electrons on the 2n l atoms of the chromophoric cationic chain, rather than by a single formula ... 

In tetranudear dyes such as in Scheme 69 with two independent chromophoric chains, providing the chains are of different length, the absorptions maxima lie at the same A as each of the component cyanine but chains of equal lengths produce a shift of the two A, one toward longer... 

Chromophore (Section 13 21) The structural unit of a mole cule principally responsible for absorption of radiation of a particular frequency a term usually applied to ultraviolet visible spectroscopy... 

Table 7.9 Electronic Absorption Bands for Representative Chromophores Table 7.10 Ultraviolet Cutoffs of Spectrograde Solvents Table 7.11 Absorption Wavelength of Dienes Table 7.12 Absorption Wavelength of Enones and Dienones Table 7.13 Solvent Correction for Ultraviolet-Visible Spectroscopy Table 7.14 Primary Bands of Substituted Benzene and Heteroaromatics Table 7.15 Wavelength Calculation of the Principal Band of Substituted Benzene Derivatives...

Molecules with two or more isolated chromophores (absorbing groups) absorb light of nearly the same wavelength as does a molecule containing only a single chromophore of a particular type. The intensity of the absorption is proportional to the number of that type of chromophore present in the molecule. Representative chromophores are given in Table 7.9. 

Appreciable interaction between chromophores does not occur unless they are linked directly to each other, or forced into close proximity as a result of molecular stereochemical configuration. Interposition of a single methylene group, or meta orientation about an aromatic ring, is sufficient to insulate chromophores almost completely from each other. Certain combinations of functional groups afford chromophoric systems which give rise to characteristic absorption bands. 

TABLE 7.9 Electronic Absorption Bands for Representative Chromophores... 

Many pharmaceutical compounds contain chromophores that make them suitable for analysis by UV/Vis absorption. Products that have been analyzed in this fashion include antibiotics, hormones, vitamins, and analgesics. One example of the use of UV absorption is in determining the purity of aspirin tablets, for which the active ingredient is acetylsalicylic acid. Salicylic acid, which is produced by the hydrolysis of acetylsalicylic acid, is an undesirable impurity in aspirin tablets, and should not be present at more than 0.01% w/w. Samples can be screened for unacceptable levels of salicylic acid by monitoring the absorbance at a wavelength of... 

Different light-absorbing groups, called chromophores, absorb characteristic wavelengths, opening the possibility of qualitative analysis based on the location of an absorption peak. 

The concept of a chromophore is analogous to that of a group vibration, discussed in Section 6.2.1. Just as the wavenumber of a group vibration is treated as transferable from one molecule to another so is the wavenumber, or wavelength, at which an electronic transition occurs in a particular group. Such a group is called a chromophore since it results in a characteristic colour of the compound due to absorption of visible or, broadening the use of the word colour , ultraviolet radiation. 

Hydantoin derivatives show weak absorption in the uv-visible region, unless a part of the molecule other than the imidazohdinedione ring behaves as a chromophore (13) however, piC values have been determined by spectrophotometry in favorable cases (14). Absorption of uvby thiohydantoins is more intense, and the two bands observed have been attributed to n — tt and n — tr transitions of the thiocarbonyl group (15,16). Several piC values of thiohydantoins have been determined by uv-visible spectrophotometry (16). 

Resonance Raman Spectroscopy. If the excitation wavelength is chosen to correspond to an absorption maximum of the species being studied, a 10 —10 enhancement of the Raman scatter of the chromophore is observed. This effect is called resonance enhancement or resonance Raman (RR) spectroscopy. There are several mechanisms to explain this phenomenon, the most common of which is Franck-Condon enhancement. In this case, a band intensity is enhanced if some component of the vibrational motion is along one of the directions in which the molecule expands in the electronic excited state. The intensity is roughly proportional to the distortion of the molecule along this axis. RR spectroscopy has been an important biochemical tool, and it may have industrial uses in some areas of pigment chemistry. Two biological appHcations include the deterrnination of helix transitions of deoxyribonucleic acid (DNA) (18), and the elucidation of several peptide stmctures (19). A review of topics in this area has been pubHshed (20). 

---