On the Transition from a Biomimetic Molecular Switch to a Rotary Molecular Motor

Abstract

The experimental investigation of the unidirectional motion characterizing the photoisomerization of single-molecule rotary motors, requires accessible lab prototypes featuring an ECD signal sensitive to the geometrical and electronic changes occurring during an ultrafast reactive process. Here we report a combined experimental/computational study of a candidate obtained via the asymmetrization of a light-driven biomimetic molecular switch. We show that the achieved motor has an ECD band remarkably sensitive to the isomerization motion and it is therefore suitable for time-resolved ECD studies. However, we also find that, unexpectedly, the synthesized motor isomerizes on a time-scale longer than the sub-picosecond time measured for the achiral parent. A result that points to alternative candidates conserving a high reaction speed.

Designing light-driven rotary molecular motors

“…Similar results were observed for a structurally related p -HDBI motor. 60 These studies provide a basis for the growth of a novel generation of photochemically-driven rotary motors, fortified with a biomimetic framework.…”

“…Biomimetic motors based on p -HDBI have also been prepared, with similar values for the photoisomerisation QY ( E → Z = 23%). 60 …”

“… 59 More recently, motors based on the biologically relevant fluorophore p -hydroxybenzylidenedimethylimidazolone ( p -HDBI) have also been developed. 60 …”

Design, Synthesis and Characterization of a Visible‐Light‐Sensitive Molecular Switch and Its PEGylation Towards a Self‐Assembling Molecule

“…[38,39] In this last design effort, we were inspired by the structure of the Green Fluorescent Protein (GFP) fluorophore 5-(4-hydroxybenzylidene)-1H-imidazol-2(5H)-one (p-HBDI), to transform an efficient emitter into an LDMS that featured a sub-picosecond E/Z photoisomerization (HBDI-LPs, see Figure 1A) under UV light exposure. [38,39] In parallel, some of us have developed the concept of "affinity polymerization" based on the molecular recognition between 3-phenylbenzofulvene derivatives (i. e. 6-MO-BF3k [40] reported in Figure 1C) mediated by intermolecular π-stacking interactions. [41][42][43][44] In these systems, spontaneous polymerization occurs in the apparent absence of catalysts or initiators and involves the exocyclic double bond of these trans-diene monomers.…”

“…To this scope, we have prepared analogues positively charged N‐alkylated or N‐protonated indanylidene pyrroline Schiff bases (NAIPs and NHIPs respectively), which perform ultra‐fast double bond photoisomerization [33–37] . The same biomimetic approach was then used to design a negatively charged LDMS [38,39] . In this last design effort, we were inspired by the structure of the Green Fluorescent Protein (GFP) fluorophore 5‐(4‐hydroxybenzylidene)‐1 H ‐imidazol‐2(5 H )‐one ( p ‐HBDI), to transform an efficient emitter into an LDMS that featured a sub‐picosecond E /Z photoisomerization ( HBDI‐LPs , see Figure 1A) under UV light exposure [38,39] …”