Photoinduced Ionic to Neutral Phase Transition in TTF-CA Studied by Time-Resolved Infrared Vibrational Spectroscopy

Abstract

We studied the photoinduced ionic to neutral phase transition in tetrathiafulvalene-p-chloranil (TTF-CA) using time-resolved infrared vibrational spectroscopy. By monitoring the charge sensitive b 1u ν 10 band of CA after photoexcitation by a 1.55 eV pulse, we found that the photoinduced N-phase has the same charge of the N-phase in thermal equilibrium and there is no charge variation during the photoinduced phase transition. We also found that the photoinduced N-phase grows through at least two steps over 300 ps.

Time-Resolved Infrared Vibrational Spectroscopy of the Photoinduced Phase Transition of Pd(dmit)2 Salts Having Different Orders of Phase Transition

“…Although the situation is slightly different, a similarly slow process (∼100 ps) was observed in the PIPT from the low-to high-temperature phase in TTF-CA (tetrathiafulvalene-p-chloranil). 17,62 In this slow process, proliferation of the domain occurs; however, this crystal also undergoes a first-order thermal phase transition, and there is probably a bottleneck slowing the proliferation process.…”

“…Photoinduced phase transition (PIPT) is a cooperative phenomenon in which a few electrons injected by photoirradiation trigger a change in macroscopic physical properties through various interactions. − Since such phase transitions are ultrafast and efficient, they have attracted significant attention from the scientific viewpoint as well as for applications to ultrafast photoswitching devices. However, PIPT is very difficult to understand and utilize because it involves many nonequilibrium states including photoinduced phases from the Franck–Condon state to the thermal equilibrium state on the femtosecond to nanosecond time scales.…”

“…These previous studies have successfully observed photoinduced changes in the electronic structure. Recently, methods to observe molecular and lattice structure, such as time-resolved diffraction − and time-resolved vibrational spectroscopy, − have been developed, and relatively slow structural dynamics in PIPT have attracted more attention. Time-resolved diffraction using ultrashort X-rays or electron-beams is a direct method, but requires large facilities and is still under development.…”

Photo-Induced Structural Changes at a Surface οf Organic Single Crystals Observed by Vibrational Sum Frequency Generation Spectroscopy

“…Therefore using the p polarized laser, VSFG is sensitive to detect the a g modes induced by the dimerization of TCNQ molecules [5]. Time-resolved infrared vibrational spectra in reflectivity are measured using a broadband femtosecond mid-infrared pulse and a MCT (HgCdTe) linear array detector [8], and the polarization of light is aligned to detect the TCNQ dimerization. The crystal is grown by evaporating the solvent slowly at room temperature and is obtained with black in color and in an elongated-shape [1,9].…”

Photoinduced Phase Transition in Strongly Electron-Lattice and Electron–Electron Correlated Molecular Crystals

“…Thus, PIPT has been intensively investigated in CT complexes because of its scientific complexities and various potential applications. For example, the photoinduced neutral-ionic (N-I) phase transition in tetrathiafulvalene-p-chloranil (TTF-CA), which exhibits the so-called "domino-effect", is the first example of PIPT [4] and has been extensively studied by numerous researchers [5][6][7][8][9].…”