Photochemistry of Alkenes, Alkynes and Related Compounds

The results of a study of the yas-phase photocheaistry of ethylene at 183 na have been reported.  

A review lecture has dealt with the isomerization of anthryl 13 

25 to -78 C when the reaction is carried out in benzene. A similar effect is also observed in toluene and p-xylane. In these 

Reversible cw, rra j-isomerism has been reported following the irradiation of micellar aggregates of the photochromic surfactants (1) in water.  

tran -Isomerization. - The crowned benzophenones (1, n = 1 or 2) have been used as sensitizers for the isomerization of 1,2-dichloroethene, which is brought about by irradiation at 365 nm and was shown to be cation dependent. This results in variations of the Z/ ratio. The highest ZjE ratios were obtained when the sensitizer was (1, n = 1) with Li or Mg as the cations or with (1, n = 2) where the cation is Na+ or Ionic photodissociation of the 3-arylallyl 

1 Stilbene and Related compounds. The influence of sol-gel transformations on the emission spectra of cis and trans-stilbene has been assessed. The results of INDO/S calculations on stilbene has estimated the influence of the excited states involved in isomerization. The photostability of solutions of trans-stilbene to high-energy excitation with a XeCl laser has been studied. Geometric isomerization of both cis- and trans-stilbene is the result of irradiation of the compounds in NaY zeolites. A photostationary state composed of 65% cis and 35% trans is 

Lewis and his co-workers have continued their investigations into DNA hairpins with a variety of stilbene diether linkages. In the present report they have examined systems based on the linkers (3) and (4). The rotaxane formed between the stilbene derivative (5) and a-cyclodextrin (CD) does not undergo ,Z-isomerization. Contrary to this the complex of (6) with the p-CD isomerizes slowly on irradiation. The behaviour of the stilbene (6) is different and irradiation in a-CD brings about isomerization with a quantum yield of 0.06 for the E,Z process. The quantum yield for the reverse isomerization is 0.71. These values are to be compared with 0.17 and 0.79 for the isomerization in solution. The authors suggest that the irradiation of (6) in the CD brings about a movement 

The photoequilibration of cis and trans-stilbene in N-butylpyridinium chloride-AICI3, an ionic liquid system, occurs via the radical cations of the stilbene. A different mechanism is operative when irradiations are carried out in l-ethyl-3-methylimadazolium chloride-AlCh. Some aspects of photochemistry in ionic liquids, such as cis-trans-isomerism, have been discussed in a recent publication.  

The photophysical and photochemical properties of a series of stilbene derivatives such as (7) and (8) have been investigated. The fluorescence spectra of l,T-bi(benzocyclobutylidene), a rigid stilbene, has been investigated.  

Further studies on the photoisomerization of ci5-cyclohexene and cycloocta-1,3-diene have been reported. Again the work has focused on enantiodiffer-entiation. In this case a series of optically active chiral sensitisers (3) have been used under conditions where solvent and temperature have been varied. Some of the o-disubstituted and tetra substituted amide sensitisers afford mixtures with enantioisomeric excesses of 14%. The influence of pressure and temperature on the asymmetric photochemistry of cyclooctene has been reported. A variety of chiral sensitisers were used. Some of these are shown in (4). Other work has shown that aromatic phosphates, phosphinates and phosphines (e.g. 5-8) can also sensitise the isomerism of cyclooctene. Moderate stationary-state ratios were obtained. 

Results from an examination of energy transfer within steroidal molecules have been presented. This work has examined the derivatives (9) and (10) among many others. Triplet-triplet energy transfer is detected by the isomerism of the remote alkene in ring D following excitation of the DPSO group and detailed kinetic studies were carried out. 

---

IIH3 Photochemistry of Alkenes, Alkynes and Related Compounds... 

---