Double Stereochemical Labeling in Stilbene Photochemistry:  Tracing Phenyl Rotation Reveals Stereochemically Distinct Reaction Pathways for Formation of the E Photoproducts

Synthesis of Twist−Twist π-Conjugated Di-sec-alkylstilbenes and Stilbene Polymers

“…tert-Butyl-substituted TTPC stilbenes have allowed unique mechanistic investigations of bromine addition 6,7 and phenyl rotation in stilbene photochemistry. 8 Electroluminescence in organic compounds was thrust into prominence with the discovery of polymer luminescence in a stilbene relative, poly(p-phenylene vinylene). 9 Subsequent, rapid advances in organic light-emitting diodes (OLED) led to commercial, flat-panel displays.…”

“…Stilbenes have played a central role in many aspects of organic chemistry. − Sufficiently large substituents on the double bond rotate the phenyl groups 90° out of the molecular plane creating twist−twist π conjugation (TTPC). , Novel features can result. tert -Butyl-substituted TTPC stilbenes have allowed unique mechanistic investigations of bromine addition , and phenyl rotation in stilbene photochemistry …”

“…However, 1-(2-methylphenyl)-2,2-dimethyl-1-propanone failed to couple under low-valent titanium conditions, demonstrating an alkyl group cannot be extended from the ortho position of the benzene ring. Although 1-(3-methylphenyl)-2,2-dimethyl-1-propanone readily coupled, in subsequent steps the presence of the meta substituent prevented low-valent titanium coupling to extend the TTPC system to analogues of 2a , b …”

Small Scale Reactor for Ultraviolet Photochemistry

“…Switching wavelengths by switching lamps can favorably increase yields. For example, the product ratio in a sterically congested stilbene isomerization increased from 1:5 to 1:1 with a change in lamp (1).…”