RELATIONSHIP BETWEEN CHEMICAL REACTIVITY AND PHOTOCHROMISM ... RELATIONSHIP BETWEEN CHEMICAL REACTIVITY

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  • RELATIONSHIP BETWEEN

    CHEMICAL REACTIVITY AND PHOTOCHROMISM USING 1,2-DITHIENYLETHENE-BASED

    MOLECULAR SWITCHES

    by

    Vincent Lemieux B.Sc. Honours, McGill University 2003

    THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

    DOCTOR OF PHILOSOPHY

    In the Department of Chemistry

    © Vincent Lemieux 2008

    SIMON FRASER UNIVERSITY

    Summer 2008

    All rights reserved. This work may not be reproduced in whole or in part, by photocopy

    or other means, without permission of the author.

  • ii

    Approval

    Name: Vincent Lemieux

    Degree: Doctor of Philosophy

    Title of Thesis: Relationship Between Chemical Reactivity and Photoactivity Using 1,2-Dithienylethene-Based Molecular Switches

    Examining Committee:

    Chair Dr. David J. Vocadlo Assistant Professor, Department of Chemistry

    Dr. Neil R. Branda Senior Supervisor Professor, Department of Chemistry

    Dr. Ross H. Hill Supervisor Professor, Department of Chemistry

    Dr. Vance E. Williams Supervisor Associate Professor, Department of Chemistry

    Dr. Peter D. Wilson Internal Examiner Associate Professor, Department of Chemistry

    Dr. Michael M. Haley External Examiner Professor, Department of Chemistry University of Oregon

    Date Defended/Approved: July 22, 2008

  • iii

    Abstract

    Molecular systems with integrated chemical reactivity and photochromic

    functions are potentially beneficial for the development of novel functional materials.

    Rationally designed photoresponsive compounds can be used to regulate chemical

    reactivity using light, and such systems could significantly influence both synthesis and

    drug delivery by increasing efficiency and decreasing undesired side-reactions or side

    effects. Chemical reactivity can also be employed to control the photochromic behaviour

    of photoswitches, providing a locking mechanism and enabling chemical detection

    through facile monitoring.

    Dithienylethene-based molecular switches are particularly well-suited to the

    development of functional systems with integrated chemical reactivity functions since

    they can be toggled between two thermally stable and structurally unique isomers when

    irradiated with light of the appropriate wavelengths. Dithienylethene derivatives exhibit

    significant differences between their ring-open and ring-closed forms, which can

    influence their reactivity. Alternatively, multiple strategies permit the regulation of their

    photochromic properties through chemical reactions or interactions. The research

    presented in this thesis focuses on the development of novel approaches to integrate

    photochromism and chemical reactivity.

    First, the concept of reactivity-gated photochromism is introduced and

    demonstrated using a spontaneous and mild chemical reaction. Results show that

  • iv

    non-photoswitchable molecules can be rendered photoactive by creating the

    dithienylethene architecture using the Diels-Alder cycloaddition.

    The use of the dithienylethene architecture as a photocleavable group that

    combines reactivity-gated photochromism and photogated reactivity is then presented.

    This approach is based on the Diels-Alder reaction between photostable dienes and

    dienophiles to generate photoswitchable dithienylethene derivatives. The photoresponsive

    unit is employed to regulate the reverse cycloaddition, enabling selective and sequential

    photorelease of the small dienophile auxiliary.

    Finally, the Lewis acidity of a boron-containing dithienylethene derivative is

    photomodulated. Upon exposure to light of the appropriate wavelengths, the

    isomerisation of the dithienylethene backbone causes a bond rearrangement of the 1,3,2-

    dioxaborole unit, directly affecting the electron density of the boron centre and changing

    the Lewis acidity of the atom.

    Keywords: Photochromism, reactivity-gated photochromism, photogated reactivity, dithienylethenes, Diels-Alder reaction, photorelease, Lewis acidity.

  • v

    Dedication

    À Christine, à mes parents, Sylvie et Yvon,

    et aux montagnes de la Colombie-Britannique

  • vi

    Acknowledgements

    I would like to thank my senior supervisor Neil Branda for his guidance and

    motivation. In addition, I extend my thanks to the members of my supervisory committee,

    Vance Williams and Ross Hill, for their helpful advice. Thanks to Philippe Reutenauer

    for useful discussions concerning the retro-Diels-Alder reaction. Special thanks to Simon

    Gauthier for his help with the photorelease project presented in Chapter 3 and to Daniel

    Spantulescu for his guidance in improving the synthesis of α-hydroxyketones as

    discussed in Chapter 4. I would like to acknowledge Kim K. Baldridge for carrying out

    calculations concerning the boron project. I am also grateful to the Branda group

    members, past and present, for sharing their knowledge and experience, especially David

    Sud who shared his bench with me for 3 years and Chad Warford who shared his

    fumehood in the last 2 years.

    Several technicians and specialists at Simon Fraser University contributed to

    various extents to my projects: Mei-Keng Yang for elemental analyses; Hongwen Chen

    and Philip Ferreira for mass spectrometry; Andrew Lewis, Marcy Tracey, and Collin

    Zhang for NMR services.

    Finally, my family and friends have provided invaluable moral support and

    encouragements; thanks to all of them. I also acknowledge Les Cowboys Fringants,

    Malajube, Radiohead, The Offspring, Metallica, and all the others who inspired me with

    their music in the laboratory and during the redaction of this thesis.

    Merci Christine, sans toi je n’aurais jamais réussi.

  • vii

    Table of Contents

    Approval ............................................................................................................................ ii

    Abstract............................................................................................................................. iii

    Dedication ...........................................................................................................................v

    Acknowledgements .......................................................................................................... vi

    Table of Contents ............................................................................................................ vii

    List of Figures................................................................................................................... xi

    List of Schemes.............................................................................................................. xxii

    List of Equations ......................................................................................................... xxvii

    List of Tables ..................................................................................................................xxx

    List of Abbreviations ................................................................................................... xxxi

    List of Molecules ..........................................................................................................xxxv Numbered molecules of Chapter 2 ............................................................................xxxv Numbered molecules of Chapter 3 .......................................................................... xxxvi Numbered molecules of Chapter 4 ........................................................................ xxxviii

    Chapter 1: Introduction ....................................................................................................1 1.1 Light and chemical reactivity ..........................................................................1 1.2 Photochromism................................................................................................2 1.3 Dithienylethene (DTE) derivatives..................................................................5

    1.3.1 General description of DTE derivatives ......................................................5 1.3.2 The photochemical ring-closing reaction of DTEs......................................6 1.3.3 Photostationary state....................................................................................7 1.3.4 Photochemical side reactions of DTEs ........................................................8 1.3.5 Synthetic versatility of DTE derivatives......................................................9 1.3.6 Effects of the ring-closure reaction on DTEs ............................................10

    1.4 Integration of photochromism and chemical reactivity.................................12 1.5 Modulation of chemical reactivity using DTE derivatives............................14

    1.5.1 Modulation of reactivity using geometric and steric differences in DTEs..........................................................................................................14

    1.5.2 Modulation of reactivity using electronic differences in DTEs.................18 1.6 Modulation of DTEs photochromism using chemical r