A second generation motorized nanocar was designed, synthesized, and imaged. To verify structural integrity, NMR-based COSY, NOESY, DEPT, HSQC, and HMBC experiments were conducted on the intermediate motor. All signals in (1)H NMR were unambiguously assigned, and the results were consistent with the helical structure of the motor. The nanocar was deposited on a Cu(111) surface, and single intact molecules were imaged by scanning tunneling microscopy (STM) at 5.7 K, thereby paving the way for future single-molecule studies of this motorized nanocar atop planar substrates.

Unimolecular submersible nanomachines (USNs) bearing light-driven motors and fluorophores are synthesized. NMR experiments demonstrate that the rotation of the motor is not quenched by the fluorophore and that the motor behaves in the same manner as the corresponding motor without attached fluorophores. No photo or thermal decomposition is observed. Through careful design of control molecules with no motor and with a slow motor, we found using single molecule fluorescence correlation spectroscopy that only the molecules with fast rotating speed (MHz range) show an enhancement in diffusion by 26% when the motor is fully activated by UV light. This suggests that the USN molecules give ∼9 nm steps upon each motor actuation. A non-unidirectional rotating motor also results in a smaller, 10%, increase in diffusion. This study gives new insight into the light actuation of motorized molecules in solution.

We have observed the mixed-valence and radical cation dimer states of a glycoluril-based molecular clip with tetrathiafulvalene (TTF) sidewalls at low concentration (1 mM) at room temperature. This molecular clip has four consecutive anodic steps in its cyclic voltammogram, which suggests a sequential oxidation of these TTF sidewalls to generate species existing in several distinct charge states: neutral monomers, mixed-valence dimers, radical cation dimers, and fully oxidized tetracationic monomers. The observation of characteristic NIR spectroscopic absorption bands at approximately 1650 and 830 nm in spectroelectrochemistry experiments supports the presence of intermediary mixed-valence and radical cation dimers, respectively, during the oxidation process. The stacking of four TTF radical cations in the dimer led to the appearance of a charge-transfer band at approximately 946 nm. Nanoelectrospray ionization mass spectrometry was used to verify the tricationic state and confirm the existence of other different charged dimers during the oxidation of the molecular clip.

At room temperature, four-adamantane-wheeled nanocars thermally diffuse on an air–glass interface. A line-scan imaging method was developed to improve the time resolution in tracking their surface movement. The fast imaging technique disclosed that the four-wheeled nanocars diffuse on glass surfaces in a quasi-random two-dimensional (2D) diffusion manner. That is, they have a high tendency to keep a linear diffusion trajectory at a short time scale, which is consistent with the wheel-rolling mode diffusion. The nanocar molecules lose the directionality over time, indicating that other diffusion modes, e.g., pivoted movement, may also contribute to their thermal diffusion at room temperature. The characteristic linear movement time for the two types of nanocar molecules in this study was ∼1.2 s, from which the activation energy for the nanocars to pivot away from the original direction was estimated to be ∼65 kJ mol–1. Finally, it was shown that using the line-scanning method the diffusion coefficient of quasi-random 2D diffusing nanocars can be accurately estimated to be ∼10.0 × 10–16 m2 s–1.

The design and synthesis of a 4,4‐difluoro‐4‐bora‐3a,4a‐diaza‐s‐indacene (BODIPY)‐based motorized nanocar and two control molecules for single‐molecule fluorescence microscopy studies (SMFM) is described. The nanocar incorporates a fast rotatory light‐driven motor (3 MHz at 25 °C) that is expected to move in circles. In addition, two control molecules without wheels and bearing a fast or a slow motor (2 revolutions per hour) were also synthesized to investigate the role of the motor, wheels, and the photocompatibility of the light‐driven rotary motor with the BODIPY fluorophore. The high quantum yields of 0.40–0.78 of these molecules make them suitable for future SMFM studies.

We have synthesized a new molecular switch-based on a macrocycle-clip complex-whose switching behavior not only can be controlled through the use of either K+-[2,2,2]cryptand or NH4+-Et3N systems but also provides color changes that are visible to the naked eye; consequently, this system operates as a two-input NOR functioning molecular logic gate.

Single-molecule fluorescence microscopy at an air–solid interface severely suffers from photobleaching. In this study, we evaluated using a triplet-state quencher cyclooctatetraene (COT) group to enhance the photostability of cy5-attached molecular machines. For single-dye-modified nanocars, the photobleaching lifetime of the dye was extended by 2.1 times after the attachment of the COT group. For two-COT-two-dye-attached unimolecular submersible nanomachine (USN) molecules, both one-step and two-step photobleaching of the dyes were observed, similar to those cy5-USNs without COT protection. The fraction of one-step photobleaching events was nearly a constant under different laser powers, indicating that one-step photobleaching is a single-photon process and that the product of the first photobleaching event destroys the second dye. The COT-cy5-USNs showed a larger fraction of two-step photobleaching events as compared to cy5-USNs, indicating that the COT group provides further protection for the second dye from the oxidative product generated in the first dye photobleaching process. Overall, the protected, doubly labeled COT-cy5-USN molecules have a total photobleaching lifetime extended by 2.4 times over unprotected cy5-USN molecules or by 3.3 times over unprotected, single cy5-labeled molecules. This study shows the potentials and the limits of using triplet quencher COT to protect fluorescent dyes at the air–glass interface.

No abstract