Phosphorescence in solution

Of particular interest in the application of cyclodextrins is the enhancement of luminescence from molecules when they are present in a cyclodextrin cavity. Polynuclear aromatic hydrocarbons show virtually no phosphorescence in solution. If, however, these compounds in solution are encapsulated with 1,2-dibromoethane (enhances intersystem crossing by increasing spin-orbit coupling external heavy atom effect) in the cavities of P-cyclodextrin and nitrogen gas passed, intense phosphorescence emission occurs at room temperature. Cyclodextrins form complexes with guest molecules, which fit into the cavity so that the microenvironment around the guest molecule is different from that in... 

In fluid solutions only the third mechanism is of importance in transfer of triplet excitation. The trivial mechanism is usually excluded because most molecules do not phosphoresce in solution, and the second mechanism seems to be excluded because the transition moments for the T - S process in the donor and the T - S transition of the acceptor should both be vanishingly small. An interesting possibility which has yet to be explored experimentally is that heavy atom-containing solvents might so enhance T <- S transition probabilities that long-range triplet energy transfer may become important. 

The heavy-atom elfeci can be utilized for measuring phosphorescence in solution. In Figure 5.15 the luminescence spectrum of 1,4-dibromonaphthalene... 

Room-temperature phosphorescence in solution has been observed in organized media containing micelles. With miceltcs. the analyte is incorporated into the core of the micelle, which serves to protect the triplet stale. Cyclodexlrin molecules, which are... 

In recent years, there has been a rapid growth in the number of publications that report the use of surfactant monomers or micelles to improve the analytical perfommice of various spectroscopic (UV-visible spectrophotometry, fluorimetry, phosphorimetry, chemiluminescence and atomic spectroscopy), and electrochemical (especially amperometry) methods [1]. The unique properties of surfactants have been recognized as being very helpful to overcome many problems associated with the use of organic solvents in these methods. Surfactant-modified procedures yield sensitivity and/or selectivity improvements in determinations commonly performed in homogeneous solution, whereas certain analytic methods (such as room-temperature phosphorescence in solution) can be exclusively conducted in organized media. 

L. J. Cline Love, M. Skrilec and J.G. Habarta, Analysis by Micelle-Stabilized Room Temperature Phosphorescence in Solution, Anal. Chem., 52 754 (1980). 

Cline Love LJ, Skrilec M, and Habarta JG (1980) Analysis by micelle stabilized room temperature phosphorescence in solution. Analytical Chemistry 52 754-759. 

Yang C-H, Li S-W, Chi Y, Cheng Y-M, Yeh Y-S, Chou P-T, Lee G-H, Wang C-H, Shu C-F (2005) Heteroleptic cyclometalated iridium(III) complexes display blue phosphorescence in solution and solid state at room temperature. Inorg Chem 44 7770-77780... 

Since S -T - energy gaps in organic molecules vary considerably, it is easy to find acceptor-donor pairs in which only triplet excitation transfer is energetically feasible. Such systems have been extensively exploited for study of the factors which influence the efficiency of Reaction (8). Three methods have been used to measure rates of triplet excitation transfers in solution. The first involves measurement of the phosphorescence lifetimes of the donor molecule as a function of the concentration of the acceptor molecule (Sandros and Backstrom, 1962). The general applicability of this method is severely limited by the fact that few molecules phosphoresce in solution. The second, more generally applicable, method uses the flash... 

---