ULTRAFAST OPTICAL SWITCHING - 2-PULSE RESPONSE OF AN ELECTRON DONOR-ACCEPTOR-DONOR SUPERMOLECULE

An electron donor-acceptor-donor molecule consisting of two 8'-apo-bet a-carotene (CAR) donors rigidly attached to the two-electron acceptor N,N'-diphenyl-3,4,9,10-perylenebis(dicarboximide) (PBDCI) acts as a ph otochromic molecular switch on a picosecond time scale. Excitation of this molecule with a 200 fs laser pulse at 420 nm results in formation of a single polyene cation accompanied by one-electron reduction of t he acceptor. Application of a second 200 fs, 420 nm laser pulse 10 ps after the first pulse results in oxidation of the second polyene and f urther reduction of PBDCI to its dianion state. The singly- and doubly -reduced PBDCI electron accepters absorb light strongly at 720 nm and 570 nm, respectively. Thus, this molecule undergoes picosecond time sc ale photochromic changes that depend on whether or not a second laser pulse has been applied to the system during the lifetime of the initia lly formed ion pair. Because the photochromism occurs solely via elect ron transfers, this molecule switches significantly faster than most p hotochromic molecules that must undergo changes in molecular structure .