Revised steady-state fluorescence spectrum and nature of the reactive S1 state of cis-stilbene in solution

We measured steady-state fluorescence of cis-stilbene in solution, by carefully separating the contribution of coexisting trace amount of trans isomer. The obtained ‘pure’ fluorescence spectrum of cis-stilbene shows a broad structureless band (peaked around 420 nm) extending to the wavelength region as long as 700 nm. Compared to the fluorescence intensity from the coexisting trans isomer, the oscillator strength of the cis fluorescence was evaluated as 0.17, which indicated that the S1 state of cis-stilbene is an optically allowed state.