A new compound, 1.2-bispyratyl ethylene was synthesized and characterized by spectroscopic methods and elemental analysis.
In UV-VIS spectra, $(n.π^{*})^1$band which is expected to be separated from $(π,π^{*})^1$ band was bidden under strong($π.π^{*}$) absorption. From salt effects on fluorescence and photoreduction, it is believed that $(n.π)^1$ state has about the same energy as $(π.π^{*})^1$ state. The fluorescence yield from $(π.π^{*})^1$ state was 0.025 at 77˚K compared to near unity for stilbene at the same temperature and guantum yield for photoreduction is also very low, less than 0.1. From this results, it is concluded that singlet excited state of BPE has one or more very efficient relaxation processes other than fluorescence and photoreduction, very likely an efficient intersystem crossing because of ($n.π^{*}$) and ($π.π^{*}$) mixing.
Direct and sensitized photochemical cis$\rightleftharpoons$trans isomerization of BFE was studied utilizing salt effect, solvent effect sensitization, quenching and photostionary state. It is concluded that twisted ($π.π^{*}$) triplet state is responsible for direct photoisomerization of BPE in contrast to direct stilbene isomerization which is believed to undergo through twisted ($π.π^{*}$) singlet state.
