Photoisomerization of cis,cis- to trans,trans-1,4-diaryl-1,3-butadienes in the solid state: the bicycle-pedal mechanism.

The photoisomerizations of crystalline or powdered cis,cis-1,4-diphenyl- and 1,4-di(o-tolyl)-1,3-butadienes (cc-DPB and cc-DTB) to the trans,trans isomers were studied at room temperature. The progress of the reactions was monitored by fluorescence spectroscopy, powder X-ray diffraction, (1)H NMR, and high-performance liquid chromatography. Conversions to the trans,trans isomers were as high as 90% for cc-DPB and 20% for cc-DTB.

Photoisomerization of cis,cis-1,4-diphenyl-1,3-butadiene in glassy media at 77 K: the bicycle-pedal mechanism.

The cis-trans photoisomerization of cis,cis-1,4-diphenyl-1,3-butadiene in a soft isopentane glass at 77 K gives significant two-bond photoisomerization in contrast to solution and hard glassy media where only one-bond photoisomerization takes place.

Photoisomerization of cis,cis-1,4-diphenyl-1,3-butadiene in the solid state: the bicycle-pedal mechanism.

The cis-trans photoisomerization of crystalline or powdered cis,cis-1,4-diphenyl-1,3-butadiene (cc-DPB) was studied at room temperature. The progress of the reaction was monitored by fluorescence spectroscopy, powder X-ray diffraction, 1H NMR and HPLC. High conversions (up to 90%) to the trans,trans isomer were observed in a crystal to crystal reaction.

Photoisomerization of cis-1-(2-naphthyl)-2-phenylethene in methylcyclohexane at 77 K: no hula-twist.

The cis-trans photoisomerization of cis-1-(2-naphthyl)-2-phenylethene (c-NPEA and c-NPEB) was studied in methylcyclohexane glass at 77 K. The progress of the reaction was followed by fluorescence spectroscopy. Formation of the extended trans conformer (t-NPEB) is revealed by the growth of sharp vibronic bands on the broad structureless fluorescence spectrum of c-NPE.