Photochromism of phenoxynaphthacenequinones

1. Photochromism of phenoxynaphthacenequinones Reto Borm, Walter Fischer, Dominik Heger, Bogdan Tokarczyk and Jakob Wirz Photochem. Photobiol. Sci., 2007, 6, 552-559 Miyasaka Lab. M1 Toshiyuki UMESATO

2. Contents Introduction Photochromism Photochromic compounds Results and Discussion Transient absorption Picosecond pump-probe experiments Nanosecond kinetic and spectrographic laser flash photolysis Energy diagram for the photochromic transformation Summary

3. A B Quick Property Changes Optical memories, Optical switches Absorption spectra, Dipole moment, Polarizability …. Fundamental chemical reaction processes Elucidation of reaction mechanism The reaction having time origin Photochromism Photoinduced reversible isomerization in a chemical species between two forms without changes of molecular weight. (at least, one pathway should be photoinduced.) hn hn’ or D

4. Photochromic compounds Azobenzene Spiropyran UV UV Vis., D Vis. DAE PNI UV 405nm Vis. D, 490nm HABI Salicylideneaniline hn hn D hn’,D

5. Photochromic compounds cis – trans isomerization … Azobenzene UV Vis., D trans-form cis-form Molecular length , Polarity … Photoresponsive functional polymer

6. UV Vis., D trans-form cis-form Photochromic compounds cis – trans isomerization … Photomechanics of Liquid-Crystalline Elastomers T. Ikeda, et al, Angew. Chem. Int. Ed., 47, 4986-4988(2008)

7. Photochromic compounds Ring-opening and ring-closing reaction … diarylethene UV Vis. Open form Closed form Thermal stability of both isomers Fatigue resistance Quick response Photochromism in the solid phase Photoactuator

8. UV Vis. Open form Closed form Photochromic compounds Ring-opening and ring-closing reaction … diarylethene Photoactuator S. Kobatake, et al, Nature 2007, 446, 778

9. Photochromic compounds Homolytic reversible cleavage of C-N bond… HABI (hexaarylbiimidazol) hn D HABI Lophyl radicals Research into radical chemistry Polymerisation initiator

10. hn D HABI Lophyl radicals Photochromic compounds Homolytic reversible cleavage of C-N bond… HABI (hexaarylbiimidazol) J. Abe, et al, Org. Lett., 10, 3105-3108(2008) Fast reversible photochromism

11. Transient species ex.) excited state, radical … Photochromic compounds Phenyl group transfer … phenoxynaphthacenequinon hn (l<450 nm) Ft-a : 32% hn (l<520 nm) Fa-t : 1.4% trans ana trans ana 1 (R=H) 2 (R=OC6H5) bir

12. Probe I Pump DA = log I0 rise DA A decay a b a b Transient absorption Transient species Reference Sample hn a → b A Reference a b

13. Picosecond pump-probe experiments trans ana Pump:270 nm 0~40 ps 40 ~ 1640 ps l / nm t / ps t / ns l / nm Vibrational relaxation&Internal conversion Intersystem crossing trans → Sχ → S1 → trans-T1 → 3bir → ana