Spectroscopic Labels

Quantum dots are useful because the wavelength of their visible emission depends on their size. Size is controlled during synthesis of the quantum dot by reaction time or other conditions. Quantum dots with different sizes can be used as spectroscopic labels in biological experiments.13... 

Figure 6.3 Energy level pattern and spectroscopic labeling of states from the schematic shell model. The angular momentum coupling is indicated at the left side and the numbers of nucleons needed to fill each orbital and each shell are shown on the right side. From M. G. Mayer and J. H. D. Jenson, Elementery Theory of Nuclear Shell Structure, Wiley, New York, 1955.

Synthetic carotenoids incorporated into multicomponent sutructures such as triad 8 have been used as spectroscopic labels to follow the flow of triplet energy and the spin dynamics in model photosynthetic reaction centers. Excitation of the porphyrin moiety in 8 yields C- P-C,.q which decays by photoinduced electron transfer to yield - "- , . This state rapidly evolves into the final charge separated state, C -P-(Liddell et al., 1997). The fact that both electron transfer steps in 8 occur even in a glassy matrix at 77K has made it possible to observe some unusual... 

Let us first consider the lowest few vertical excitations of vinoxy radical as obtained from simple CIS/6-311++G " level calculations at the X W equilibrium geometry. By default, the CIS calculation leads to the lowest three states of ground-state (doublet) multiplicity, which may be identified with the conventional spectroscopic labels A A (root = 1), B A" (root = 2), and C A (root = 3) in order of ascending energy. The calculated vertical excitation energies are 2.033, 6.728, and 6.787 eV, respectively. A sample G9X input deck to perform this calculation and carry out NBO/NRT analysis on the lowest-lying A state is shown in Example 7.1. 

We have already indicated the ground state and excited states to be coupled, i.e.- the spin-orbital states are mixed. The ground state level consists of J = 15/2 (93 6h,6 I). What we do is to label the energy states in terms of the spectroscopic label which makes the nu or contribution to its intermediate coupling makeup. Thus, for the J= 5/2 levels, we would... 

Selective analytic and spectroscopic methods for analyzing biomimetic model complexes bound to the support are rather limited, and a detailed characterization of such hybrid materials is much more challenging than of soluble molecular complexes. If local spectroscopic probes are available, IR spectroscopy, gel-phase or solid-state NMR spectroscopy, EPR spectroscopy, or (diffuse reflectance) UV-vis spectroscopy is applicable. Useful IR spectroscopic labels include CO, C=N, E-H, M=E, and M=E stretching vibrations as long as they are either very intense or are separated from the matrix vibrations. For EPR spectroscopic analysis, metal isotopes with nuclear spin 1 0 are suitable. Biologically interesting metal ions include (7 = 7/2, 99.76%), Mn I =512, 100%), Co (7 = 7/2, 100%), 3/65cu (7 = 3/2, 69.09% 7 = 3/2, 30.91%), and (7 = 5/2, 15.72% ... 

When n = 2, there are four sets of / and m quantum numbers satisfying rules (4-18) and (4-19). They are listed below with their spectroscopic labels ... 

Table 8.2 Spectroscopic labels, configurational assignments, energy level AE (kcal/mol, relative to ground singlet), and shell-character description for low-lying singlet states of Ni atom.

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