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A Molecular Rotor Based on an Unhindered Boron Dipyrromethene (Bodipy) Dye

Lookup NU author(s): Dr Mohammed Alamiry, Professor Andrew Benniston, Graeme Copley, Kenneth Elliott, Emeritus Professor Anthony Harriman, Beverly Stewart, Dr Yong-Gang Zhi

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Abstract

This work describes a fluorescent probe for following changes in the viscosity of the surrounding medium. The optical properties, fluorescence characteristics, and sensitivity to frictional forces with the surrounding medium are superior to the most commonly used molecular probe, namely dicyanovinyl julolidine. The photophysical properties of the target molecule have been recorded in a range of solvents under ambient conditions, over a wide temperature range, and as a function of applied pressure. The mechanism by which the probe responds to changes in local viscosity involves gyration of the mesophenylene ring and accompanying distortion of the dipyrrin framework, as indicated by molecular dynamics simulations. Indeed, temperature-dependence measurements have established that the activation energy is small when the solvent viscosity is relatively low, but there is a turnover to strong activation control at very high viscosity. A small but definite solvent dependence appears when the viscosity is varied by the application of high pressures and this can be traced to differences in the elasticity of the surroundings. Unusually for such fluorescent rotors, there is no indication that the excited state involves charge-transfer interactions. The rotor also responds to changes in the polarizability of the solvent, as induced by changes in applied pressure, and to the extent of polymerization of a monomer. The various experimental observations made at low viscosity are consistent with diffusive motion of the wave packet along the excited tate potential curve until finding a sink that strongly coupled to the highly distorted ground state. © 2008 American Chemical Society.


Publication metadata

Author(s): Alamiry MAH, Benniston AC, Copley G, Elliott KJ, Harriman A, Stewart B, Zhi Y-G

Publication type: Article

Publication status: Published

Journal: Chemistry of Materials

Year: 2008

Volume: 20

Issue: 12

Pages: 4024-4032

ISSN (print): 0897-4756

ISSN (electronic): 1520-5002

Publisher: American Chemical Society

URL: http://dx.doi.org/10.1021/cm800702c

DOI: 10.1021/cm800702c


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