Conformational changes in photoexcited (R)-(+)-1,1′-Bi-2-naphthol studied by time-resolved circular dichroism

Conformational changes following photoexcitation of (R)-(+)-1,1'-bi-2-naphthol, are studied with a time-resolved circular dichroism (CD) experiment. Two wavelengths are investigated. For lambda = 237 nm, we observe a bleaching of the ground-state absorption and a transient CD structure. Thanks to a coupled-oscillator calculation, we can attribute this effect to a decrease of the dihedral angle. For A = 245 rim, excited-state absorption and CD are observed. All these effects are solvent-dependent. In particular, it is shown that dynamics is slower in a protic solvent, which is attributed to hydrogen-bonding of the hydroxy groups with the solvent.