Solid-state quantum yield

The Matsuura method (57) compares the photolysis result of a solution actinometer with that of a thin crystalline film of equal surface area after exposure. Thus, evaporation of a solution containing the photoreactive substrate results in a thin crystalline film on the glass wall of a test tube, which is subsequently exposed to actinic radiation in a merry-go-round type photolysis apparatus. To test for complete absorption of the incident photons within the crystalline film, the evaporation process is carried out at various concentrations of the substrate, which leads to films of different thickness. If the yield of photoproduct after a certain exposure time is independent of the concentration of the original solution before evaporation, complete absorption of all actinic photons is established. The quantity of the photons absorbed by the crystalline film is then estimated by parallel photolysis of a 0.1 M solution of 2,4,6-triisopropylbenzophenone in methanol solution, which has a well-established quantum yield of 0 = 0.52 (58). The volume of this actinometer solution in the test tube is adjusted so that the crystalline film and the solution exhibit irradiated surfaces of identical size. In summary, this method provides approximate estimates of solid-state quantum yields however, differences in the reflection of the... 

Ito Y, Matsuura T. A simple method to estimate the approximate solid state quantum yield for photodimerization of trans-cinnamic acid. J Photochem Photobiol 1989 50 141-145. Ito Y, Matsuura T, Fukuyama K. Efficiency for solid-state photocyclization of 2,4,6-triisopropylbenzophenones. Tetrahedron Lett 1988 29 3087-3090. 

Photoreactivity of carbonyl compounds in the solid state is little understood. Many factors such as rates of elementary processes, lifetimes of intermediates, crystal structure, and looseness of crystal packing must be considered to elucidate the mechanism (cf. Fig. 3). In addition to the traditional X-ray crystallography, the usefulness of solid-state quantum yield measurements is exemplified. 

Correspondingly, even in the solution irradiation of er -butyl, enone 52 led to the Type C photoproducts only. However, the solid-state reaction was more selective in giving exclusively Type C photoproduct 53 (note Scheme 8.13). Additionally, the solid-state quantum yield was remarkably high... 

According to spin statistics, only 25% of all excited states generated by charge injection should be singlet states capable of spin-permitted radiative decay (fluorescence), and thus the maximum possible EL efficiency for a polymer LED should be 25% of the polymer s solid-state PL efficiency. Thus, the maximum theoretical efficiency for a polymer LED using a fluorescent polymer should be only 3-6% (25% of emissive states X 60% solid-state quantum yield for emissive states X 20-40% of photons escaping). 

Figure 3. Energy diagram for 1064 nm excitation of PuFg(g). The 5f electron states of PuF6 are shown at the left. The solid arrows Indicate photon absorption or emission processes. The wavy arrows indicate nonradiative processes by which excited states of PuF6 are lost. Comparison of observed fluorescence photon yields versus the fluorescence quantum yield expected for the 4550 cm" state indicate that the PuFg state initially populated following 1064 nm excitation may dissociate as shown.

A tetrameric structure with the Zn40 core can also be formed with the 7-azaindolate ligand, [Zn40(C7H5N2)6], and has been structurally characterized. The tetramer displays intense photoluminescence at 448 nm in the solid state and 425 nm in acetonitrile with a lifetime and quantum yield of 0.1 ps and 0.17 ps respectively.280... 

By examining any correlation between excimer formation (as evidenced by characteristic excimer fluorescence) and dimerization quantum yield, one could perhaps determine whether dimerization is dependent upon prior excimer formation. Excimer fluorescence from anthracene solutions at room temperature is negligible although it has been observed in the solid state at low temperature.<75) Unfortunately, the data for substituted anthracenes allow no firm conclusions to be drawn. Some derivatives dimerize but do not exhibit excimer fluorescence. Others both dimerize and show excimer fluorescence. Still others show excimer fluorescence but do not dimerize and finally, some neither dimerize nor show excimer fluorescence. Hopefully, further work will determine what role excimer formation plays in this photodimerization. 

Stokes-shifted tautomer emission and high quantum yield in solid state (10%), DHBO was successfully used as an energy transfer donor in the photochromic switching system [88]. 

A certain balance should be kept in distortion of the thiophene planarity as a way to prevent the formation of interchain aggregates. Introducing two substituents at positions 3 and 4 of PT allows a shift of the emission through the entire visible range and prevents interchain interactions (resulting in a smaller decrease of the quantum yield in the solid state compared to solution). Highly crowded disubstituted PTs 418 421 show very low luminescence efficiency already in solution (Table 2.5) due to substantial distortion of the backbone [107,498],... 

---