An Antilock Molecular Braking System

Abstract

A light-driven molecular brake displaying an antilock function is constructed by introducing a nonradiative photoinduced electron transfer (PET) decay channel to compete with the trans (brake-off) → cis (brake-on) photoisomerization. A fast release of the brake can be achieved by deactivating the PET process through addition of protons. The cycle of irradiation-protonation-irradiation-deprotonation conducts the brake function and mimics the antilock braking system (ABS) of vehicles.

Fate of photoexcited trans-aminostilbenes

“…Trans-aminostilbenes are a class of p-donor-acceptor (D-A) systems that have been investigated as fluorescent probes [1][2][3][4][5][6], cell imaging dyes [7][8][9], and the active materials in a variety of optoelectronic devices such as organic light-emitting diodes [10,11], dye-sensitized solar cells [12][13][14], nonlinear optics [15][16][17][18][19][20], and molecular switches [21,22]. These applications are all associated with the electronically excited states, in which the lowest singlet excited state (S 1 ) possesses a significant degree of charge separation as a result of intramolecular charge-transfer (ICT) from the amino to the stilbene moiety upon photoexcitation.…”

Wholly Synthetic Molecular Machines

“…[33][34][35] Sandwich-like p-metal complexes can serve as imilar purpose: for example, Aida [36,37] has employed ferrocene as the rotary axle in his molecular scissors. On account of their susceptibility to photo-isomerization, double bonds have been incorporated into molecular machines when bending movements are deemed to be desirable in addition to rotation.B oth azobenzene [38][39][40][41][42][43][44] ands tilbene [45][46][47][48] have been used widely in the construction of photo-responsive molecular machines. [49] Bending movementsc an also be supplied by diarylethene [50][51][52][53] and spiropyrans, [54][55][56][57][58] both of which undergo reversible ring-closing and ring-opening reactions.…”

Light‐Gated Molecular Brakes Based on Pentiptycene‐Incorporated Azobenzenes

“…[7,[10][11][12][13][14][15][16][17][18][19] One such prototypei s" molecular brakes", which possess two or more states that differ in the rotationr ate of ar igid subunit (rotor) about as ingle bond;t hese states could be interconverted by using external stimuli (fuels). [19][20][21][22][23][24] Among the various forms of fuel, light has the advantages of rapid input, remote control, and no waste deposition. However,l ight gating often suffers from incomplete switching.…”

“…The reversible cis-trans (Z-E)p hotoisomerization of alkenes and azobenzenes has provided an important basis for the design of light-gated molecular devices. [19][20][21][22][23][24][25][26][27][28] The on-off switching efficiency depends on the quantum yields of the E! Z (F EZ )a nd Z!E isomerizations (F ZE )a nd on the relative molar absorptivity of the E (e E )a nd Z isomers (e Z )a tt he irradiation wavelengths, according to Equation (1), in which [E]/[Z] PSS denotes the E/Z molar ratio at the photostationary state (PSS).…”