Ultrafast Bidirectional Dihydroazulene/Vinylheptafulvene (DHA/VHF) Molecular Switches:  Photochemical Ring Closure of Vinylheptafulvene Proven by a Two-Pulse Experiment

Abstract

The photochromic couple dihydroazulene/vinylheptafulvene (DHA/VHF) is an established system for molecular switching. The photoinduced ring opening of the thermally stable dihydroazulene proceeds in the picosecond time regime with subsequent rapid relaxation to the electronic ground state. So far it was not possible to reverse the reaction photochemically. It was always found that the back reaction proceeds thermally on a longer time scale. In the case of the cyanophenyl-DHA derivative utilized in the present study, this is accounted to s-cis/s-trans isomerization of the primarily formed s-cis VHF. Since this particular isomerization takes much longer than nanoseconds, we now successfully applied a second visible femtosecond pulse subsequent to the initial UV pulse (25 ps delay) achieving ring closure of the primarily formed s-cis VHF. The now bidirectional photoswitching was monitored by the changes in the cw spectrum. As a result, the DHA/VHF system is found to be a multifold switchable system by itself: it is both a very fast photoreversible switch and a photochemical/thermal switch with a thermal lock mode.

Development of Ultrashort Pulse Lasers for Ultrafast Spectroscopy

“…Ultrafast dynamics of the various chemical reactions and carrier dynamics in condensed matter like semiconductors have been studied using the ultrashort visible-NIR pulse or its SH. Elucidation of ultrafast dynamics in various systems accelerates development in various applications like photosensors [3][4][5], ultrafast optical switches [6][7][8], and ultrafast optical memories [9][10][11]. Many interesting ultrafast dynamics in biological systems including photosynthesis [12][13][14] and vision processes [15][16][17], were studied by ultrafast spectroscopy using the visible or UV pulse lasers.…”

Development of Sub 10 fs Visible-NIR, UV, and DUV Pulses and Their Applications to Ultrafast Spectroscopy

“…The method can also be used for the study of photophysical and photobiological processes like vision [5] and photosynthesis [6]. Ultrafast dynamics provides key information for the study of photosensors [7][8][9], optical memory [10][11][12], and optical switches [13][14][15].…”

Single-molecule detection of dihydroazulene photo-thermal reaction using break junction technique

“…We became interested in exploring the dihydroazulene ( dha )/vinylheptafulvene ( vhf ) system1516 as previous studies have shown light-controlled conductance switching of dha derivatives in a silver nanogap fabricated using sublimable molecules and also bias-induced switching for a junction operating in the Coulomb blockade regime1718. Fabrication of junctions by sublimation puts some constraints on the molecules that can be studied in regard to molecular weight and stability.…”