EXCITED-STATE TRANSIENT SPECTROSCOPY OF ANTHRACENE BASED PHOTOCHROMICSYSTEMS

In this study. picosecond time resolved excited state absorption spect roscopy is employed to determine the evolution and lifetime of the pho tochromic states in anthracene based molecular systems and the contrib ution of conformational changes. The unsubstituted bianthrone shows a broad transient absorption which peaks in the region of 600 nm. Equiva lent measurements on anthracene give similar results indicating that t his transition originates from a locally excited state on the anthrone ring system. Upon substitution of the bianthrone, an additional trans ient absorption at 700 nm evolves within 10 ps after excitation. This is assigned to a twisted state in which the excited state is stabilise d by a strong conformational change. The metastable nature of the stat e is confirmed by time delay measurements.