Enlightening dynamic functions in molecular systems by intrinsically chiral light-driven molecular motors

Abstract

Chirality is a fundamental property which plays a major role in chemistry, physics, biological systems and materials science.

Excited State Dynamics in Unidirectional Photochemical Molecular Motors

“…32,33,42 The rotor typically contains a single chiral center to provide the stereochemistry required for unidirectional motion, while the stator can be modified, allowing it to be linked to other molecules or to surfaces, as the application requires. 43,44 By modifying the nuclear and electronic structures of rotor and stator, both stereochemistry and steric crowding can be manipulated to control the barrier to THI, such that these second generation motors are capable of megahertz rotational frequencies. 32 It is convenient to begin our discussion of PMM excited state dynamics with 2 rather than with 1 since this structure is the most widely used and has been studied in most detail by both ultrafast spectroscopy and quantum mechanical and molecular dynamics calculations.…”

“…The first generation motor 1 demonstrated the proof of principle and mechanism of PMM function. , Quantitative study of its photochemical behavior revealed a high quantum yield for photoisomerizaton, as expected for the fundamental stilbene architecture coupled to strong steric repulsion; yields in the region of 60–85% were reported. , However, the barrier to THI in 1 is high, such that at room temperature the maximum operational frequency is restricted to a few hertz, yielding an efficiency that is too low for many applications. This limitation stimulated a great deal of synthetic effort and resulted in a family of motors with the general structure 2 (Figure ) comprising a larger aromatic ring system called a “stator” (typically based on a fluorene, 2 , or tricyclic aromatic) linked by a double bond axle to a smaller “rotor”. ,, The rotor typically contains a single chiral center to provide the stereochemistry required for unidirectional motion, while the stator can be modified, allowing it to be linked to other molecules or to surfaces, as the application requires. , By modifying the nuclear and electronic structures of rotor and stator, both stereochemistry and steric crowding can be manipulated to control the barrier to THI, such that these second generation motors are capable of megahertz rotational frequencies . It is convenient to begin our discussion of PMM excited state dynamics with 2 rather than with 1 since this structure is the most widely used and has been studied in most detail by both ultrafast spectroscopy and quantum mechanical and molecular dynamics calculations.…”

From Organic Fragments to Photoswitchable Catalysts: The OFF–ON Structural Repository for Transferable Kernel-Based Potentials

“…Despite the inherent difficulties, creating a more general database that could be used to train ML potentials to describe, for example, the chemical reactivity and the rich conformational and configurational behavior of flexible medium- and large-sized functional organic molecules would be highly valuable. Particularly, it is not only the unique chemical components but also the dynamic movements of these organic molecules that are intrinsically linked to their functionality (e.g., the flexible nature of organocatalysts influences both selectivity and reactivity). , Such problems are particularly well illustrated by photoswitchable organocatalysts (i.e., photochromic molecules featuring a catalytic site that can be toggled between two stereoelectronic states with different reactivities and flexibilities when acted upon by appropriate wavelengths of light). − While data-driven discovery pipelines exist to engineer molecular photoswitches with desired photophysical properties, − fewer studies have focused on investigating chemical reactivity as a function of the rich conformational and configurational behavior of these organocatalysts. Add to this the requirement that each configurational state [e.g., ( E )- or ( Z )-isomer] uniquely corresponds to an “ON” or “OFF” reactivity state, and it becomes clear that a thorough description of conformational states is needed to fully grasp the catalytic properties.…”

Red Circularly Polarized Luminescence from Dimeric H-Aggregates of Acridine Orange by Chiral Induction

“…However, the latter, displaying tunable CD and CPL, have shown promising applications in various photon-based technologies. 2,9,10 The stereocenters of inherently chiral molecules often impose a chiral arrangement in their selfassembled nanostructures. In such cases, the coupled motion of the electric transition dipole moments provides a circular component.…”

“…While the chiroptical signals such as circular dichroism (CD) and circularly polarized luminescence (CPL) emerging from isolated molecular systems − have been well expounded, those from assembled ones are much less understood. However, the latter, displaying tunable CD and CPL, have shown promising applications in various photon-based technologies. ,, The stereocenters of inherently chiral molecules often impose a chiral arrangement in their self-assembled nanostructures. In such cases, the coupled motion of the electric transition dipole moments provides a circular component. ,, Consequently, the transition also acquires magnetic dipole character, giving rise to CD and CPL.…”