Spectroscopic and Theoretical Identification of Two Thermal Isomerization Pathways for Bistable Chiral Overcrowded Alkenes

• Published in: Chemistry : a European journal Vol. 22; no. 38; pp. 13478 - 13487
• Main Authors: Kistemaker, Jos C. M., Pizzolato, Stefano F., van Leeuwen, Thomas, Pijper, Thomas C., Feringa, Ben L.
• Format: Journal Article
• Language: English
• Published: WEINHEIM Blackwell Publishing Ltd 12.09.2016; Wiley; Wiley Subscription Services, Inc
• Subjects: Alkenes; bistable switches; Chemistry; Chemistry, Multidisciplinary; computational chemistry; Dynamics; Fatigue strength; Helicity; High temperature; Irradiation; Isomerization; Liquid chromatography; molecular switches; Photochemicals; photoisomerization; Physical Sciences; Science & Technology; Selectivity; Switches; thermal isomerization; Thermal stability; Ultraviolet radiation; MOLECULAR-ORBITAL METHODS; HELIX INVERSION; LIGHT; photoisomerization; computational chemistry; thermal isomerization; CIS-TRANS-ISOMERIZATION; 2ND-ROW ELEMENTS; VALENCE BASIS-SETS; UNIDIRECTIONAL ROTATION; STRUCTURAL MODIFICATION; MOTORS; molecular switches; ROTARY MOTION; bistable switches
• ISSN: 0947-6539; 1521-3765; 1521-3765
• DOI: 10.1002/chem.201602276

Chiroptical molecular switches play an important role in responsive materials and dynamic molecular systems. Here we present the synthesis of four chiral overcrowded alkenes and the experimental and computational study of their photochemical and thermal behavior. By irradiation with UV light, metastable diastereoisomers with opposite helicity were generated through high yielding E–Z isomerizations. Kinetic studies on metastable 1–4 using CD spectroscopy and HPLC analysis revealed two pathways at higher temperatures for the thermal isomerization, namely a thermal E–Z isomerization (TEZI) and a thermal helix inversion (THI). These processes were also studied computationally whereby a new strategy was developed for calculating the TEZI barrier for second‐generation overcrowded alkenes. To demonstrate that these overcrowded alkenes can be employed as bistable switches, photochromic cycling was performed, which showed that the alkenes display good selectivity and fatigue resistance over multiple irradiation cycles. In particular, switch 3 displayed the best performance in forward and backward photoswitching, while 1 excelled in thermal stability of the photogenerated metastable form. Overall, the alkenes studied showed a remarkable and unprecedented combination of switching properties including dynamic helicity, reversibility, selectivity, fatigue resistance, and thermal stability. Molecular switches: The synthesis of four chiral overcrowded alkenes and the experimental and computational study of their photochemical and thermal behavior is presented. The alkenes studied showed a remarkable and unprecedented combination of switching properties including dynamic helicity, reversibility, selectivity, fatigue resistance, and thermal stability.