Ultrafast Optical Switching from an Ionic to a Neutral State in Tetrathiafulvalene-p-Chloranil (TTF-CA) Observed in Femtosecond Reflection Spectroscopy

Abstract

Ultrafast optical switching from an ionic ( I) to a neutral ( N) state in TTF-CA was observed in femtosecond reflection spectroscopy. Charge transfer excitation in the I phase produces N donor ( D0) acceptor ( A0) strings within 2 ps. These initial N states decay with a lifetime of 300 ps at 4 K, but rather multiply leading to macroscopic I-N conversion within 20 ps at 77 K just below the N-I transition temperature T(NI). Near T(NI), we also found the evidence for the coherent motion of the macroscopic N-I domain boundary with a period of 85 ps.

State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

“…Consequently the probed dynamics may be different: in particular nucleation processes may be strongly influenced by the vicinity of the surface and bulk dynamics by the propagation process. Moreover, the results of both optical and diffraction measurements unambiguously agree on the threshold behavior (Koshihara et al, 1999;Iwai et al, 2002;Tanimura 2004;Okamoto et al;2004;Collet et al, 2003). When the TTF-CA is excited in the region of the charge-transfer band (i.e.…”

“…Recent optical pump-probe reflectivity measurements have evidenced the photoinduced change of electronic state, both for the I-to-N and for the N-to-I transformations, on the 100 ps time scale (Koshihara et al, 1999, Iwai et al, 2002, Okamoto et al, 2004, Tanimura 2004. These laser-induced states relax to their thermodynamical stable phases in less than 1 ms.…”

“…The high conversion efficiency, with many molecules transformed by a single photon, originates from cooperativity. From the X-ray and optical data, it is estimated that one photon transforms about few hundreds molecules (Koshihara et al, 1999, Iwai et al, 2002Okamoto et al, 2004;Collet et al, 2003). Low laser penetration depth is a drawback in this X-ray experiment, as X-rays probe the whole volume of such 100 mm thick crystals.…”

Infrared Investigations of the Neutral-Ionic Phase Transition in TTF-CA and Its Dynamics

“…Over the decades, a large number of ultrafast pump-probe experiments have been performed on TTF-CA in order to explore the photo-induced phase transition (PIPT) that occurs in this one-dimensional charge-transfer compound, most of them confined to the femto-and picoseconds time range [35,58,[69][70][71][72][73][74][75][76][77][78][79][80]. The studies were mainly restricted to low temperatures (typically 4 K) or very close to the phase transition (T ≤ T NI ).…”

Femtosecond motion picture

“…Many researches to discover and elucidate the new phenomena are actively carried out in the fields, such as physics [1,2,3,4,5], chemistry [6,7,8,9,10], and biology [11,12,13,14]. In these researches, however, only the relation between the time evolution and other physical quantity, such as energy to time, is discussed.…”