Ultrafast polyene dynamics: the ring opening of 1,3-cyclohexadiene derivatives.

The light activated ring-opening reaction of the 1,3-cyclohexadiene chromophore finds application in optical control, optical switching, optical memory, light activated molecular machines, photobiology, photochromic materials, and conformation-specific photocatalysts. The development of ultrafast spectroscopic methods and powerful computational methods have accelerated the understanding and facilitated the application of this important chromophore in a wide range of systems. Here we look at the current state of theoretical and experimental understanding for the ring-opening reaction of the isolated cyclohexadiene molecule and the ring-opening reactions of substituted cyclohexadienes, including fulgides, diarylethenes, and provitamin D.

Ultrafast ring-opening reactions: a comparison of alpha-terpinene, alpha-phellandrene, and 7-dehydrocholesterol with 1,3-cyclohexadiene.

The excited and ground state dynamics of a series of 1,3-cyclohexadiene derivatives and their hexatriene photoproducts are studied using ultrafast broadband UV-visible transient absorption spectroscopy. The substitution pattern around the cyclohexadiene backbone alters the excited state potential energy surface in the Franck-Condon region as evidenced by changes in the excited state absorption and fluorescence properties of the systems. Unsubstituted 1,3-cyclohexadiene and alpha-phellandrene exhibit no excited state absorption while a strong excited state absorption in the visible spectral region is observed for both alpha-terpinene and Provitamin D3.

Photochemical ring-opening and ground state relaxation in α-terpinene with comparison to provitamin D3.

Ultrafast broadband UV-visible transient absorption spectroscopy is used to characterize the photochemistry of α-terpinene, a 1,4-disubstituted-1,3-cyclohexadiene natural product. These results are compared with experiments probing the analogous ring-opening reaction of 7-dehydrocholesterol (DHC, provitamin D3) and the subsequent relaxation of previtamin D3. The major experimental results are as follows: (1) Like DHC, but unlike 1,3-cyclohexadiene, α-terpinene exhibits a broad excited state absorption (ESA) spectrum in the visible.