Excited state transient spectroscopy of anthracene based photochromic systems

In this study, picosecond time resolved excited state absorption spectroscopy is employed to determine the evolution and lifetime of the photochromic states in anthracene based molecular systems and the contribution of conformational changes. The unsubstituted bianthrone shows a broad transient absorption which peaks in the region of 600 nm. Equivalent measurements on anthracene give similar results indicating that this transition originates from a locally excited state on the anthrone ring system. Upon substitution of the bianthrone, an additional transient absorption at 700 nm evolves within 10 ps after excitation. This is assigned to a twisted state in which the excited state is stabilized by a strong conformational change. The metastable nature of the state is confirmed by time delay measurements.