Ultrafast dynamics of a molecular rotor in chemical and biological nano-cavities

Abstract

Molecular rotors have become indispensable tools to monitor several important processes inchemistry and biology owing to their sensitivity towards viscosity. Despite their importance, less attention has been paid to understand the excited state properties of molecular rotors.Recently, Maroncelli and coworkers unraveled the excited state photochemistry of julolidine based molecular rotor, 9-(2-carboxy-2-cyano)vinyl julolidine (CCVJ), and claimed that CCVJ is not a simple rotor probe. Unlike other molecular rotors, the photoisomerization is believed to be the main non-radiative decay pathway for this molecule. Inspired by their report, herein, we have tried to understand how the excited state dynamics of CCVJ is getting affected inside the nano-cavities of cyclodextrins (CDs) and human serum albumin (HSA) protein using steady-state and femtosecond fluorescence up-conversion techniques. We have observed pronounced enhancement in fluorescence quantum yield, when CCVJ is encapsulated in CDs (β-and γ-CD) and HSA. Femtosecond up-conversion study reveals that the ultrafast dynamics of CCVJ is drastically retarded inside the nano-cavities of CDs and protein. All these results suggest that photoisomerization, which is believed to be major nonradiative decay pathway of CCVJ, is severely restricted inside the above mentioned biomimetic and biological nano-cavities. The molecular pictures of orientations of CCVJ inside the nano-cavities of CDs and protein have been discussed by theoretical and molecular modeling studies. We believe the present results might be helpful in exploiting this molecule more in biological and viscosity sensing applications.

Fluorescent Molecular Rotors for Viscosity Sensors

“…It was shown that such physical parameters influence molecular rotational motion,r esulting in changes to the FL quantumy ield. [86] In a rectangulart ube, when the flow patterns of CCVJ followed a parabolic profile andt he velocity of the fluid increased, the FL intensity linearly increased over ac ertain range. CCVJ exhibited similar behavior in fluidic chambers,v alidating its utility as a probe forshear stress and fluid flow.…”

Interaction of a Julolidine-Based Neutral Ultrafast Molecular Rotor with Natural DNA: Spectroscopic and Molecular Docking Studies

“…36 DCVJ has also been used to study different complex molecular systems, such as protein aggregates 37−40 and supramolecular assemblies. 25,30 Recently, DCVJ has been used as a turn-on fluorescence sensor in different applications related to nucleic acid. For example, Wu et al have shown that DCVJ can selectively bind to the abasic sites of DNA, resulting in large enhancement in its emission.…”

On the possibility to accelerate the thermal isomerizations of overcrowded alkene-based rotary molecular motors with electron-donating or electron-withdrawing substituents

“…To date, a variety of interesting applications of synthetic rotary molecular motors have been reported [ 43 – 46 ], such as in molecular transport [ 44 ] and in viscosity sensing [ 45 , 46 ]. A key requirement for such applications is that the motors are able to reach high rotational frequencies under ambient conditions [ 27 , 47 ].…”