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Insights for designing mechanochromic spiropyrans from first principles dynamics and minimum energy pathways

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Title: Insights for designing mechanochromic spiropyrans from first principles dynamics and minimum energy pathways
Author(s): Cremar, Lee
Director of Research: Martinez, Todd J.
Doctoral Committee Chair(s): Martinez, Todd J.
Doctoral Committee Member(s): Moore, Jeffrey S.; Dlott, Dana D.; Hirata, So
Department / Program: Chemistry
Discipline: Chemistry
Degree Granting Institution: University of Illinois at Urbana-Champaign
Degree: Ph.D.
Genre: Dissertation
Subject(s): Mechano-chemistry Spiropyran Mechano-chromophore First Principles
Abstract: The energy needed for a chemical reaction usually comes in the form of heat or light, which may alter the arrangement of reactant molecules on the ground state or place them on an excited state to surmount an energy barrier. An alternative and less well-explored way of initiating a chemical reaction is to use an applied force to distort the reactant molecules along a specific reaction coordinate. Recent experiments have demonstrated that the nature of the applied force can have a significant effect on the distribution of reaction products. This may allow the development of novel stress-responsive materials. In this work, we use first principles dynamics and constrained optimization approaches to investigate the mechanochemical activity of a spiropyran molecule. When a particular bond is broken, the spiropyran changes color. In combination with an understanding of the specific reaction products enhanced by applied forces, this can be exploited to create a mechano-chromophore, which changes color according to the distribution of stress in a polymeric material. Our simulations explore the amount of applied force required to induce bond rupture and the specific mechanism of bond rupture for different directions and magnitude of the applied force. We use the steered molecular dynamics method in combination with “on the fly” solution of the electronic structure problem, allowing arbitrary bond rearrangement in response to the applied force. The nature of the minimal energy pathway (MEP) on the force modified potential energy surface (FMPES) was investigated and utilized to determine reaction rate expressions within the context of transition state theory.
Issue Date: 2012-09-18
URI: http://hdl.handle.net/2142/34565
Rights Information: Copyright 2012 Lee D. Cremar
Date Available in IDEALS: 2012-09-18
Date Deposited: 2012-08
 

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