Spectroscopy and Imaging

UV-femtosecond time-resolved circular dichroism (TRCD) spectroscopy has been used to study the ultrafast changes of chirality in a small molecular biological paradigm sample, 7-dehydrocholeserol (7-DHC). Upon UV-photoexcitation, 7-DHC undergoes a ring opening to produce previtamin D3 and two of the chiral centers of 7-DHC are removed, which impacts the overall chirality of the molecule. Here, measurements of this chirality change connected to the ring opening of 7-DHC with an unprecedented time-resolution of 280 fs in the UV are reported. With this method a previously described discrepancy concerning the photophysics of 7-DHC was clarified. With our set-up the relaxation time of the chirality change was measured to be 1-2 ps, which corresponds to the shortest time-constant in the transient absorption (TA) measurements, allowing us to assign that time-constant to the ring opening.