Synthesis and Rxns
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Introduction to the Synthesis of Photochromes: Spiropyrans & Diarylethenes Stefan Hecht Department of Chemistry Humboldt-Universität zu Berlin SFB 658 Kolloquium – June 16, 2011 Focus of this presentation cis/trans isomerization ring-closing/-opening metal complexes L N N 9,0 Å hν N N N hν hν' / Δ 6,3 Å N N Fe N O Ar N Ar 15-18 D 3-4 D ¾ azobenzenes (stilbenes) ¾ imines ¾ hemithioindigos Ar hν' / Δ N O Ar ¾ spiropyrans/spirooxazines Part One: Spiropyrans ¾ diarylethenes ¾ fulgimides ¾ porphyrins ¾ phthalocyanins hν hν' R S S R open R S S R closed PROPERTY CHANGES LUMO LUMO based on structural reorganization and differences in conjugation and/or dipole moment HOMO macroscopic HOMO scale meso Part Two: Diarylethenes molecular Part One: Spiropyrans Moore and coworkers Nature 2009, 459, 68. Feringa and coworkers Science 2005, 309, 755. Spiropyrans’ basics NO2 hν1 (UV) N O spiropyran Numbering for nomenclature: NO2 hν2 (Vis) / Δ N O merocyanine Electronic structure: Conformational dynamics of the merocyanine N. P. Ernsting, T. Arthen-Engeland, J. Phys. Chem. 1991, 95, 5502. Review: V. I. Minkin, Chem. Rev. 2004, 104, 2751. Effect of substitution τ1/2 = 104 s (in EtOH for R=CO2CH3) τ1/2 = 100 ps (in 1-propanol) = 2 s (in methylcyclohexane for R=OMe) undergoes intersystem crossing (ISC) during excitation follows singlet pathway h SP 1 SP* CTC + TTC Solvatochromism of merocyanine Synthesis of spiropyrans Synthesis of indole precursors Fischer Fischer indole indole synthesis synthesis route route condensation mono alkylation double alkylation condensation Bischler Bischler indole indole synthesis synthesis route route Part Two: Diarylethenes 100 110 Irie and coworkers Science 2001, 291, 1769. Changes of Surface Morphology of a Single Crystal ring closure causes a overall contraction of the molecule open-ring closed-ring 100 vaccancies in the bulk crystal are generated 110 Irie and coworkers Science 2001, 291, 1769. Shape Control of Single Crystals changes in corner angles Irie and coworkers Science 2001, 291, 1769. changes in length Shape Control of Single Crystals - Bending light light Irie and coworkers Nature 2007, 446, 778. Diarylethenes‘ basics hν hν' R S S open R R S S closed M. Irie J. Photochemistry and Photobiology C: Photochemistry Reviews 2004, 5, 169. R Diarylethene structural design rules The “parent“ material for the diarylethenes is stilbene: This structure has to be modified by locking the Z (cis) orientation and protection of the ortho-positions of the aromatic groups. Diarylethene electronic design rules A (hetero)aromatic system has to be selected where the energy difference between the open and closed isomers is not too large. Thiophenes as well as thiazoles are among the best systems. The bridging unit has to be (photo)chemically stable and allow for a coplanar orientation to achieve high cyclization quantum yields. Stability not good good excellent excellent Planarity very good excellent good poor Diarylethene syntheses I With preformed bridges from lithiated heterocycles and perfluorocyclopentene: M. Irie et al. Tetrahedron 1998, 54, 6627. Diarylethene syntheses II Non-symmetrical switches with perfluorocyclopentene bridge: T. Kawai et al. Chem. Eur. J. 2009, 15, 1977 Diarylethene syntheses III From lithiated heterocycles and 1,2-dihaloheterocycles via Suzuki cross-coupling: e.g.: triangular terarylenes T. Kawai et al. Eur. J. Org. Chem. 2007, 3212-3218 Diarylethene syntheses IV From lithiated heterocycles and 1,2-dihalomaleimide via Suzuki cross-coupling: A. Heynderickx et al. Tetrahedron 2007, 63, 9483 Diarylethene syntheses V From lithiated heterocycles and 1,2-dihalomaleimide via Stille cross-coupling: Diarylethene syntheses VI Formation of the bridging moieties in the final step: H. Tian Adv. Mater. 2000, 12, 1597 Diarylethene syntheses VII Formation of the bridging moieties in the final step via McMurry Reaction: J. H. van Esch et al. Eur. J. Org. Chem. 2003, 155- 166 Diarylethene syntheses VIII Formation of the bridging moieties in the final step via McMurry Reaction: Y. Cheng J. Org. Chem. 2005, 70, 5001 Diarylethene syntheses IX Formation of the bridging moieties in the final step via McMurry Reaction: Y. Cheng, D. X. Zeng, M.G. Fei Org. Lett. 2003, 5, 1435 Diarylethene syntheses X Formation of the bridging moieties in the final step via intermolecular cyclizations: M. M. Krayushkin et al. Russian Chem. Bull. Int. Ed. 2001, 50, 116 Diarylethene syntheses XI Formation of the bridging moieties in the final step via intermolecular cyclizations: M. M. Krayushkin et. al Org. Lett. 2008, 10, 1319
