Absorption bands energies

Table 13.1. General Wavelength Ranges for Lowest-Energy Absorption Band of Some Classes of Photochemical Substrates...

Figure 16-36 shows the absorption spectra of thin films of four differently substituted five-ring OPVs. in contrast to the solution spectra, which show structureless low-energy absorption bands, the absorption bands of the films are structured. In the solid slate, the molecules are spatially constrained, whereas in solution different conformers exist, resulting in a distribution of accessible levels. As a consequence, some details appear in the absorption spectrum of the films which can be attributed to vibronic coupling, while, in dilute solution, the spectrum is a broad featureless band. For oct-OPV5 and Ooci-OPV5 films, the absorption maxima are red-shifted over approximately 0.1 eV relative to the solution (see Fig. 16-12). The low-energy absorption band of a thin film of Ooct-OPV5-CN" displays an appreciably larger...

The electronic absorption and emission spectra and emission lifetimes of [Ir(/x-L)(CO)2]2 (L = pz, mpz and dmpz) have been determined.529 The intense low-energy absorption band around 400 nm is assigned to a d/2 > pz electronic transition. The three complexes all emit around 740 nm at 300 K and 670 nm at 77 K. The dimer excited states are stabilized relative to monomer levels by strong metal-metal bonding. 

Table 2.2 Lowest energy absorption bands of conjugated polyenes H(CH=CH)nH...

A detailed study of the electronic structure and optical properties was published for the spiro derivative of f-Bu-PBD, Spiro-PBD (40) [108]. The vibronic structure of the lowest energy absorption band is well resolved, in solution as well as in the amorphous him. The 0-0 transition is at 351 nm (3.53 eV), the 0-1 and 0-2 vibronic bands that have a higher oscillator strength, are at 336 nm (3.69 eV) and 318 nm (3.90 eV), respectively. The fluorescence spectrum of this compound is symmetrical to the absorption spectrum with a Stokes shift of 43 nm. 

Mixed-valence chemistry was reviewed in the late 1960 s both by Robin and Day (4) and by Hush (5). Their work provided the beginnings of a theoretical background for understanding the properties of mixed-valence compounds including the low energy absorption bands which have been termed Intervalence Transfer (IT) or Metal-Metal Charge Transfer (MMCT) bands. 

Ionization of the phenol hydroxyl group in tyrosine shifts the 277-nm absorption peak to 294 nm and the 223-nm peak to 240 nm. The molar extinction coefficient for the peak of the lower energy band increases from about 1350 M l cm-1 to about 2350 M em-1 and for the higher energy band from about 8200 M cm-1 to about. 1,000 M l cm-1.113 141 In addition, the lower energy absorption band of tyrosine shows vibrational structure that is lost upon ionization of the phenol side chain. 

Extinction and absorption spectra for 0.01 jum particles with optical constants appropriate to radiation-damaged MgO (see Fig. 10.1) are also shown in Fig. 11.2. The lowest-energy absorption band among the three broad bands shows clearly in extinction but not the highest-energy band. In this instance obscuration of structure is caused by the dominance of scattering over absorption, not saturation of absorption. This is obvious from the absorption spectrum, in which all three bands are evident. To observe the band at 3.5 eV... 

Whereas proteins have their low energy absorption band at 280 nm, polynucleotides typically have maxima at 260 nm (38,500 cm ). A phenomenon of particular importance in the study of nucleic acids is the hypochromic effect. In a denatured polynucleotide the absorption is approximately the sum of that of the individual components. However, when a double helical structure is formed and the bases are stacked together, there is as much as a 34% depression in the absorbance at 260 nm. This provides the basis for optical measurement of DNA melting curves (Fig. 5-45).45,86 The physical basis for the hypochromic effect is found in dipole-dipole interactions between the closely stacked base pairs.7,86,87... 

The Mo2(S04)4 ion exhibits a 19,400 cm 1 absorption that is polarized along z in accord with the 5 -+6 transition (92). Thus Mo2(S04)4" fits the pattern of Re2X " and Mo2Xg in that the lowest energy absorption band characteristic of the quadruply bound dimers is assigned to the dipole allowed 5 - 5 transition. 

The lowest energy absorption band of P870 occurs at 870 nm. 

Irradiating a solution of the complex with UV light (365 nm) results in a decrease in the high-energy absorption bands corresponding to the ring-open isomer and an accompanying appearance of a broad absorption band... 

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). 

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