No abstract

No abstract

No abstract

A simple method for measurement of quantum yields for the singlet→triplet crossing process in solution has been developed. The compound to be tested is used as a sensitizer for one or more cis—trans isomerization reactions and the quantum yield of the induced process is measured. The results are discussed briefly

This paper critically reviews examples in the literature of photochemical cis-trans isomerization paying particular attention to the medium effect and accompanied conformational changes. A case is made that the Hula-Twist mechanism, postulated in 1985 as a photochemical reaction pathway for a polyene chromophore imbedded in a protein binding cavity such as those of rhodopsin and bacteriorhodopsin, is also a dominant reaction pathway for a diene, or a longer polyene confined in a rigid (relative to isomerization rate) medium. The conventional one-bond-flip process is the preferred reaction pathway in a fluid medium. While defining experiments are proposed, this dual mechanistic approach successfully accounts for all examples in the literature on photoisomerization reactions whether involving conformational changes or not.

The triplet excitation energies of a number of compounds have been determined by emission spectroscopy. Some of the principles involved in the choice of photosensitizers are discussed.

No abstract

No abstract