Photochemistry of Structural Analogues of Previtamin D₃:  Generality of the Wavelength-Dependent Triene Photocyclization

Abstract

Two structural previtamin D3 analogues (R = H, CH3) cyclized photochemically with a 1.4−1.8-fold increase in quantum yields over a 3-nm change in excitation wavelength. The sudden increase in quantum yields is due to the participation and mixing of both 2A and 1B excited states. At λ ≤ 306 nm, the 1B state is initially excited and then (a) partitions between isomerization to the corresponding trans triene isomers, (b) decays to the 2A state to give the corresponding cyclohexadienes, and (c) decays to the ground state. At λ ≥ 309 nm, the 2A state is directly excited to give the corresponding cyclohexadienes and the relaxation path from 1B state to the ground state or isomerization in the 1B state is diminished.

Effect of clothing varieties on solar photosynthesis of previtamin D3: an in vitro study

“…As sunlight exposure increased, the amount of previtamin D 3 increased steadily up to 30 min, followed by a slower rate at higher exposures. This may be due to the fact that at higher exposures, the reactant and photoproducts tend to reach an equilibrium (20,21). These findings seem to agree with the data reported previously (6), although the amounts of previtamin D 3 produced were less than what was found in the present investigation.…”

Generation of potentially bioactive ergosterol-derived products following pulsed ultraviolet light exposure of mushrooms (Agaricus bisporus)

“…The reaction pathway of ergosterol to its photoproducts is also dependent upon the wavelength of the incident UV source (Dauben, Zhou, & Lam, 1997;Dauben & Phillips, 1982;Havinga et al, 1960). Norval et al calculated the percentages of PD 3 , T 3 and L 3 in the photostationary state based on wavelength used for irradiation (Norval et al, 2010).…”

Reaction Control in Synthetic Organic Photochemistry: Switching between [5+2] and [2+2] Modes of Cycloaddition

“…Different reaction pathways of a single chromophore (e.g. C=C bond) can be observed by populating either singlet or triplet states.[1] Further limited modes of selection can be achieved by irradiation at userselected wavelengths, [2] through higher exited states from multiphoton absorption, [3] and by feedback-based optical control using evolutionary algorithms and pulse shapers. [4] More recently our research group has demonstrated that photon flux can be a useful parameter in controlling reaction pathways, albeit within the scale limitations imposed by tunable dye lasers.…”