Molar absorption coefficient units

When only polypyridine-type ligands are present, each mononuclear metal-based unit exhibits intense LC bands in the UV region and moderately intense MLCT bands in the visible. As it is shown by the electrochemical behavior vide supra), in the polymetallic species there is some interaction among the neighboring metal-based units. To a first approximation, however, each building block carries its own absorption properties in the polynuclear species so that the molar absorption coefficients exhibited by the compounds of higher nuclearity are huge, as it is clear by a cursory examination of the absorption data reported in Table 3. For example, the spectra of the decanuclear compounds lOB and lOC (Scheme 1 and Table 1)... 

As described in Section II.A.3, dx-bis(4,4 -dicarboxy-2,2 -bipyridine)dithiocya-nato ruthenium(II) (N3 dye) and trithiocyanato 4,4 4"-tricarboxy-2,2 6, 2"-terpyr-idine ruthenium(II) (black dye) exhibit quite good performance therefore, the systems using these two Ru dyes have been intensively investigated. However, other Ru dye photosensitizers have also been synthesized and characterized, and their performances as photosensitizers in DSSCs have been reported by many researchers [98-116]. Several kinds of electron withdrawing ligand for Ru dye photosensitizers are shown in Fig. 13. Figure 14 shows the structures of newly synthesized Ru dye photosensitizers and their absorption properties. The axis shows the molar absorption coefficient, e (i.e., absorption coefficient per M unit M 1 cm-1). 

Since the absorbance, A, is derived from a ratio (-log /// ), it is unitless. The term E, which is a proportionality constant, defines the efficiency or extent of absorption. If this is defined for a particular chromophore at a specific wavelength, the term absorption coefficient or absorptivity is used. However, students should be aware that in the older biochemical literature, the term extinction coefficient is often used. The units of E depend on the units of l (usually cm) and c (usually molar) in Equation 5.4. For biomolecules, E is often used in the form molar absorption coefficient, e, which is defined as the absorbance of a 1 M solution of pure absorbing material in a 1-cm cell under specified conditions of wavelength and solvent. The units of e are M l cm-1. To illustrate the use of Equation 5.4, consider the following calculation. 

Notice that the units of e are defined by the concentration units of the tyrosine solution M) and the dimension units of the cuvette (cm). Although E is most often expressed as a molar absorption coefficient, you may encounter other units such as A°/0, which is the absorbance of a l°/o (w/v) solution of pure absorbing material in a 1-cm cuvette at a specified wavelength, A. 

Poly(2,3-alkylthieno[3,4-fc]pyrazine)s 631 were prepared showing that adding extra thieno[3,4-fc]pyrazine units causes a large shift and an increase of the molar absorption coefficient of the low energy absorption band (08OL3513). 

Experimentally, the CD intensity is often quantified by the differential molar absorption coefficient Ae = l — r for the absorption of left-handed vs right-handed circular polarized light, where Ae and e are usually in units of L mol 1 cm-1. The conversion from Ae in L moP1 cm-1 to the molar ellipticity in deg cm2 dmoP1 is [0] = (18,0001n(10)/47r)Ae. The connection with quantities that can be calculated from first-principles theory is given by the following equation [35] ... 

The value of the molar absorption coefficient s at each temperature can be found from Table 2 by interpolation. Then p may be calculated with Eq. (43). In the calculations of this experiment, considerable care must be taken with units. It is desirable to obtain p in pascals for the statistical mechanical calculations accordingly e should be converted into units of m moP, d should be in m, and R should be in units of J mop. ... 

The three components of the self-assembled structure have complementary properties so that new functions emerge from their assembly. Dendrimer 5 has a very high molar absorption coefficient in the UV spectral region because of 12 dimethoxybenzene and 16 naphthyl units, but it is unable to sensitize the emission of an Nd ion placed in its cyclam core. The [Ru(bpy)2(CN)2] complex can coordinate (by the cyanide ligands) and sensitize the emission of Nd ions. Self-assembly of the three species leads to a quite unusual Nd complex which exploits a dendrimer and an Ru complex as ligands. Such a system behaves as an antenna that can harvest UV to VIS light absorbed by both the... 

To leant more about Beer s law, use Google to find the lUPAC Glossary of Terms Used in Photochemistry. Find how the molar absorptivity of a compound (e) is related to the absorption cross section (a). Multiply the absorption cross section by Avogadro s number and note the result. How would the result change if absorbance were expressed as A = —In (P/Pq) rather than the usual definition in terms of base-10 logarithms What are the units of a Which of the quantities e or cr is a macroscopic quantity Which is a microscopic quantity Notice that the lUPAC term for molar absorptivity is molar absorption coefficient. Which of these terms is most descriptive Explain and justify your answer. 

The sensitivity of the spectrophotometric methods is determined in terms of the molar absorption coefficient (molar absorptivity, coefficient 8), e.g., 8 = 4.86 10" 1 mole" cm" and specific absorptivity (a = e/m.mole lOOO [ml p,g cm ]. For space-saving reasons the units of 8 and a have been omitted from the text. 

The spectral overlap integral J can be expressed in terms of either wavenumbers or wavelengths (Equation 2.36). The area covered by the emission spectrum of D is normalized by definition and the quantities / and lx are the normalized spectral radiant intensities of the donor D expressed in wavenumbers and wavelengths, respectively. Note that the spectral overlap integrals J defined here differ from those relevant for radiative energy transfer (Equation 2.33). Only the spectral distributions of the emission by D /,P and, are normalized, whereas the transition moment for excitation of A enters explicitly by way of the molar absorption coefficient sA. The integrals J" and Jx are equal, because the emission spectrum of D is normalized to unit area and the absorption coefficients sA are equal on both scales. 

When the concentration of the absorbing species is expressed in mol L 1 and the optical path length in cm, the absorptivity coefficient is called the molar absorptivity coefficient (s), with units of L mol-1 cm-1, and the absorbance is expressed as... 

Principal maximum only molar absorption coefficient c calculated per mol of repeating unit... 

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