Styrene exciplex emission

In nonpolar solvents exciplex emission can be seen. Electron-rich alkanes such as 2,3-dihydropyran quench the exciplex fluorescence and also the formation of the cycloadduct. Triethylamine behaves in a similar manner. 9-Cyanophenanthrene forms cycloadducts with styrenes (Caldwell and Smith,... 

An attempt to establish the role of exciplexes in a reactive system was made by Kendler and Haas [27]. The fluorescence characteristics of the styrene-trimethylamine (TMA) adduct were studied in a supersonic jet. In the bulk, this system is known to exhibit exciplex emission and also to form photoproducts [42]. In the jet, fluorescence excitation of the STY-TMA 1 1 adduct revealed two isomers, an R-type and an E-type (Figure 9) (labeled n-type and w-type, respectively, in the original paper). The resonance-enhanced multiphoton ionization (REMPl)... 

Solvent effects on the weak exciplex emission from systems containing an aromatic nitrile and furan or an alkene are reported. The 1,2-photocycloaddi-tion reactions of methyl phenanthrene-9-carboxylate with styrenes are proposed to go by way of singlet exciplexes, partly on the basis of results from fluorescence studies of compounds such as (48). 6-Cyanophenanthridine (49) behaves like its... 

Kricka and Ledwith146 have reviewed the photochemical synthesis of cyclobutanes by dimerization of mono-olefins. Routes which involve radical cations, species of recent interest, are discussed. Yamamoto et a/.147 have shown that p-methoxystyrene undergoes photodimerization in acetonitrile solution with jp-cyanobenzene as an electron acceptor. These conditions (Pyrex filter) yield the f/wis-head-to-head-dimer [(226a), 13%]. Dimerization does not occur in non-polar solvents. A study of the emission characteristics of the styrene-cyanobenzene system shows that the fluorescence of the styrene is quenched and a broad exciplex emission is observed at 440 nm. The likely path for dimerization involves electron transfer as shown in Scheme 22. p-7V7V-Dimethylaminostyrene... 

Figure 11. Plot of the decay times and the relative intensities of the fluorescence of the styrene-TMA adduct as a function of excess energy (expressed as frequency shift from the system s origin). Note the different pattern observed for the intensity and lifetime in the case of exciplex-type emission. Adapted from Ref. [27].

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