PhotoswitchableAcids and. Georgina A. Carballo November 5, 2008

Transcription

1 PhotoswitchableAcids and Bases Georgina A. Carballo November 5, 2008

2 Why Should We Care about Photogenerated Acids or Bases? Photoresist Base insoluble Base soluble Can distinguish between irradiated and non-irradiated areas - photolithography Ito, H.; Willson, C. G.; Frechet, J. M. J.; Farrall, M. J.; Eichler, E. Macromolecules 1983, 16,

3 Applications of Photoresists Light 1. Remove mask 2. Wash exposed photoresist Remove unexposed photoresist Etch oxide layer (Plasma) Silicon Wafer Oxide Layer Photoresist Mask Microchip Fabrication 80nm Line and Space Pattern

4 Photogenerated Acids 1,8-Naphthalimide sulfonate photoacid generators Malval, J.-P.; Suzuki, S.; Morlet-Savary, F.; Allonas, X.; Fouassier, J.-P.; Takahara, S.; Yamaoka, T. J. Phys. Chem. A 2008, 112, Ito, H.; Willson, C. G.; Frechet, J. M. J.; Farrall, M. J.; Eichler, E. Macromolecules 1983, 16,

5 Photogenerated Base Light induced generation of a free amine 3,5 -dimethoxybenzoin carbamates as the protecting group Benzofuran cyclization photo-product is major Applications in polymer crosslinking, coatings and microlithography Cameron, J. F.; Willson, C. G.; Frechet, J. M. J. J. Am. Chem. Soc. 1996,118,

6 Externally Regulated Acidity and Basicity Switch Acid Empty p Orbital hν Switch Acid Switch hν Switch

7 Photochromism Reversible transformations of a single chemical species upon electromagnetic radiation where the two states show distinguishable absorption spectra (UV) (vis) Light Dark Photochromism: Molecules and Systems; 1 ed.; Rau, H., Ed.; Elsevier, 1990; Vol

8 Photochromic Molecules Diarylethenes Spirooxazines Spiropyrans Azobenzene Fulgides Berkovic, G.; Krongauz, V.; Weiss, V. Chem. Rev. 2000, 100, Matsuda, K.; Irie, M. J. Photochem. Photobiol., C 2004, 5, Yokoyama, Y. Chem. Rev. 2000, 100,

9 Photoswitchable Base Photoswitching ability given by azobenzene chromophore Z isomerization allows access to piperidine group Peters, M. V.; Stoll, R. S.; Kühn, A.; Hecht, S. Angew. Chem., Int. Ed. 2008,47,

10 Photoisomerization of Azobenzene 0.99nm 0.55 nm Hexane n,π* 432 nm (ε max =4 x 10 2 M -1 cm -1 ) π,π* 318 nm (ε max =2.2 x 10 4 M -1 cm 1 ) Hexane n,π* 430 nm (ε max = 1500 M -1 cm -1 ) π,π* 260 nm Reduced conjugation and planarity of cis-isomer Trans isomer thermally stable by Kcal/mol Change in dipole 0 3.1D Change in length of molecule Cembran, A.; Bernardi, F.; Garavelli, M.; Gagliardi, L.; Orlandi, G. J. Am. Chem. Soc. 2004, 126, Yager, K. G.; Barrett, C. J. J. Photochem. Photobiol., A 2006, 182, Crecca, C. R.; Roitberg, A. E. J. Phys. Chem. A 2006,110, Fujino, T.; Arzhantsev, S. Y.; Tahara, T. Bull. Chem. Soc. Jpn. 2002, 75,

11 Simplified Energy Level for Azobenzene- π π* * * n * n weakened πbond S 0 S 2 Torsion about the N=N bond Photochromism: Molecules and Systems; 1 ed.; Rau, H., Ed.; Elsevier, 1990; Vol. 40.

12 Simplified Energy Level for Azobenzene n π* * * n n * n πbond intact S 0 S 1 In plane inversion Photochromism: Molecules and Systems; 1 ed.; Rau, H., Ed.; Elsevier, 1990; Vol. 40.

13 Accepted Mechanisms for Azobenzene Isomerization Torsion about the N=N bond In plane inversion Photochromism: Molecules and Systems; 1 ed.; Rau, H., Ed.; Elsevier, 1990; Vol. 40.

14 Rotation about N=N Bond S 2 accessed by π π* Single bond character for N-N in S 2 Rotation about the N-N bondpossibleins 2 Lednev, I. K.; Ye, T. Q.; Matousek, P.; Towrie, M.; Foggi, P.; Neuwahl, F. V. R.; Umapathy, S.; Hester, R. E.; Moore, J. N. Chem. Phys. Lett. 1998, 290,

15 In Plane Inversion S 1 accessed by n π* Double bond character of S 1 Excitation with visible light to S 1 will result in in plane inversion Relaxation of S 2 S 1 will also result in inversion Fujino, T.; Arzhantsev, S. Y.; Tahara, T. Bull. Chem. Soc. Jpn. 2002, 75, Lednev, I. K.; Ye, T. Q.; Matousek, P.; Towrie, M.; Foggi, P.; Neuwahl, F. V. R.; Umapathy, S.; Hester, R. E.; Moore, J. N. Chem. Phys. Lett. 1998, 290,

16 Which Mechanism is Preferred? Torsion about the N=N bond In plane inversion Need to look at the transition states for both mechanisms Vibrational spectroscopy N-N ~1000 cm -1, -N=N cm -1 Photochromism: Molecules and Systems; 1 ed.; Rau, H., Ed.; Elsevier, 1990; Vol. 40. Lambert, J.; Shurvell, H.; Lightner, D.; Cooks, G. Organic Structural Spectroscopy; 1 ed.; Prentice Hall: New Jersey, 1998.

17 Raman Spectroscopy-Detecting the Structures of Excited States Inelastic collisions of photons with molecules Scattering spectroscopy Ti:sapphire laser pump 1.8 ps pulses 0 psdelay after the pulse Lambert, J.; Shurvell, H.; Lightner, D.; Cooks, G. Organic Structural Spectroscopy; 1 ed.; Prentice Hall: New Jersey, Fujino, T.; Tahara, T. J. Phys. Chem. A 2000, 104,

18 Picosecond Raman Spectroscopy- N=N Stretching N=N stretching N N N N Photoexciting(273 nm) from S 0 S 2 S 1 transient Raman detected at 0 psdelay (410 nm) Evidence of double bond character of NN at S 1 supports in-plane inversion mechanism N N Fujino, T.; Arzhantsev, S. Y.; Tahara, T. Bull. Chem. Soc. Jpn. 2002, 75, Fujino, T.; Tahara, T. J. Phys. Chem. A 2000, 104,

19 Quantum Yield - Efficiency of Photochemical Reactions Measures the efficiency of a particular light induced process For efficient photochemical process Φ 1 hν Anslyn, E.; Dougherty, D. Modern Physical Organic Chemistry; University Science Books: Sausalito, California, 2006.

20 Photostationary State Analogous to thermal equilibrium Particular proportion of isomers that does not change upon further irradiation Importance of the absorbance [T] [C] = c c t t Where ε = efficiency of absorption Φ= quantum yield Anslyn, E.; Dougherty, D. Modern Physical Organic Chemistry; University Science Books: Sausalito, California, 2006.

21 Rotationally Locked Azobenzenes Testing the photisomerizationmechanism via rotationally restricted azobenzene derivatives trans,trans trans,cis cis,cis Cyclic array of Azobenzenophanes(ABP) restricts rotation about the N=N bond Isomerizationmore plausible via inversion Increase in Φ π,π* might indicate prior relaxation to n,π* Rau, H.; Lueddecke, E. J. Am. Chem. Soc. 1982, 104, PhotoReaction Azobenzene ABP Φ t c Φt,t t,c S 1 S S 2 S Irradiation at 366 nm to the photostationary state

22 Structural Basis for Photoswitchable Base E-isomer Z-isomer Blocked Peters, M. V.; Stoll, R. S.; Kühn, A.; Hecht, S. Angew. Chem., Int. Ed. 2008, 47,

23 Features of PhotoswitchableBases Blocked basic site OFF Accessible basic Site 4aR= Me, R'= t-bu 4bR= t-bu, R'= t-bu 4cR= t-bu, R'= 2,6-Me 2 C 6 H 3 ON Conformationaly restricted Steric shielding of active site Orthogonal positioning of the chromophore Peters, M. V.; Stoll, R. S.; Kühn, A.; Hecht, S. Angew. Chem., Int. Ed. 2008, 47,

24 Photoisomerization of base vs. time UV-Vis spectrum of E and Z Isomers E Me N O O Isomers or base have different absorption spectra. Z Z N N tbu tbu E Z photoisomerizationcan be followed overtime with UV-vis spectroscopy. E Z isomerization 365 nm for 13 min Z E isomerization 400 nm for 4 min Peters, M. V.; Stoll, R. S.; Kühn, A.; Hecht, S. Angew. Chem., Int. Ed. 2008, 47,

25 Parameters Measured for Photoswitchable Bases 4aR= Me, R'= t-bu 4bR= t-bu, R'= t-bu 4cR= t-bu, R'= 2,6-Me 2 C 6 H 3 PSS (Z/E) t 1/2 (h) pkae pkaz 4a 90: NR NR 4b 90: ± ± 0.1 4c >90: ± ± 0.1 PSS (Photostationary state) irradiation at 365 nm Half life of Z isomer at 20 C in the dark Peters, M. V.; Stoll, R. S.; Kühn, A.; Hecht, S. Angew. Chem., Int. Ed. 2008, 47, Hall, H. K. J. Am. Chem. Soc. 1957, 79,

26 Henry Reaction 72% CTA-Cl R R 1 R 2 NO 2 O B R NO 2 B H R NO 2 R R 1 R 2 NO 2 OH LA R 1 O LA R 2 O R 1 R 2 Ballini, R.; Bosica, G. J. Org. Chem. 1997, 62, Luzzio, F. A. Tetrahedron 2001, 57,

27 Henry Reaction Catalyzed by a Smart Base NMR Kinetics Catalytic Activity with 10 mol% base Base k[10-5 s -1 ] k rel exp. 100% Z isomer Z E back rxn Z-isomer at PSS E-isomer E-azobenzene no catalyst PSS= Photostationary State 90:10 Peters, M. V.; Stoll, R. S.; Kühn, A.; Hecht, S. Angew. Chem., Int. Ed. 2008, 47,

28 A Photoswitchable Lewis Acid Photoswitchable N N B O Dative Bond Lewis acidity turned OFF by electron donation from N to B O Lewis acid ON when donor is away from B Yoshino, J.; Kano, N.; Kawashima, T. Tetrahedron 2008, 64,

29 Substituent Effects on the Strength of the B-N bond N N O B O OMe Electron Donating N N O B O 1a 1b 1c F Electron Withdrawing Å Stronger B-N Å Weaker B-N Å Yoshino, J.; Kano, N.; Kawashima, T. Tetrahedron 2008, 64,

30 Photoisomerization of 2-(phenylazo)-phenylboranes OMe F N N O B O N N O B O Substituent at 4' Bond Photoisomerization Irradiation at 360 nm or 431 nm to the position Length (Å) 360 nm E/Z 431 nm Z/E photostationary state H :35 98:2 OMe(EDG) :0 -- F (EWG) :46 94:6 Electron donating groups strengthen the B-N interaction Measured with NMR in C 6 D 6 EDG=Electron donating group EWG = Electron withdrawing group Electron withdrawing groups weaken the B-N interaction Yoshino, J.; Kano, N.; Kawashima, T. Tetrahedron 2008, 64,

31 Isomerization 2-(Phenylazo)-catecholboranes at 360 nm I II III Isomerizes No isomerization Isomerizes Compound E:Z ratio Bond Length Å I 65: II 100: III 69:31 -- Trend is reversed EWG strengthens B-N interaction EDG should weaken B-N interaction Kano, N.; Yoshino, J.; Kawashima, T. Org. Lett. 2005, 7,

32 Testing Lewis Acidity Followed by 11 B NMR 11 B δ21.8 ppm 11 B δ30.8 ppm E-isomer does not act as a Lewis acid Z-isomer shows Lewis acidity 11 B δ18.0 ppm 11 B δ13.8 ppm Kano, N.; Yoshino, J.; Kawashima, T. Org. Lett. 2005, 7,

33 Attempts to Diversify 2-(Phenylazo)-Phenylboranes HO R 1 R 2 HO OH N N O R 1 B O R 2 HO R 3 (HO) 2 B N N O O B N N R 3 (E)-6R 1 =R 3 =Me,R 2 =H (E)-7R 2 =R 3 =Cl,R 1 =H HO HO (E)-5a HO OH H 2 N NH 2 (E)-12 R' R' O N N O B O N N HN NH B N N (E)-8 B O O O R' R' (E)-11 (E)-9,R'=H (E)-10, R'=PH Yoshino, J.; Kano, N.; Kawashima, T. Tetrahedron 2008, 64,

34 Photoswitchable Lewis Acid B O O Resonance stabilization associated with dioxaborole ring system Claimed to be a 4n+2 system OFF ON Letsinger, R. L.; Hamilton, S. B. J. Org. Chem. 1960,25, Lemieux, V.; Spantulescu, M. D.; Baldridge, Kim K.; Branda, Neil R. Angew. Chem., Int. Ed. 2008, 47,

35 Prevention of Irreversible Oxidation (aromatization) Aromatic Aromatic Oxidation is prevented by the addition of substituents at the 2-positions Kellogg, R. M.; Groen, M. B.; Wynberg, H. J. Org. Chem. 1967, 32,

36 π-orbital Symmetry Woodward-Hoffmann Rules Thermally Photochemicaly 4n conrotatory disrotatory 4n+2 disrotatory conrotatory Conrotatory Disrotatory Woodward, R. B.; Hoffmann, R. J. Am. Chem. Soc. 1965,87,

37 Alignment of Orbitals Prior Cyclization Prior E Z isomerization Parallel Antiparallel Ring Closed Isomer Mallory, F. B.; Wood, C. S.; Gordon, J. T. J. Am. Chem. Soc. 1964,86, Uchida, K.; Nakayama, Y.; Irie, M. Bull. Chem. Soc. Jpn. 1990, 63,

38 Features of Dithienylethene Photoswitches Prevention of irreversible oxidation to aromatic compound Thermal irreversibility Sensitivity to irradiation Fatigue resistance Matsuda, K.; Irie, M. J. Photochem. Photobiol., C 2004, 5,

39 Thermal Stabilization of Diarylethenes of Ring-Closed Isomer Thermal Reversion Lifetime 3 min at 30 C Thermal Reversion Lifetime 12h at 80 C Aromatic stabilization Energies in Kcal/mol Thermal irreversibility is achieved by using substituents with low aromatic stabilization energies Irie, M.; Uchida, K. Bull. Chem. Soc. Jpn. 1998, 71, Irie, M.; Mohri, M. J. Org. Chem. 1988, 53,

40 Features of Lewis Acid OFF ON Lewis acidity is OFF due to delocalization of πelectrons that partially occupy the Boron p orbital. Lewis acidity is ON when electrons are crossconjugated to the polyene system. Lemieux, V.; Spantulescu, M. D.; Baldridge, Kim K.; Branda, Neil R. Angew. Chem., Int. Ed. 2008, 47,

41 Photocyclizationof Lewis Acid 285 nm OFF 370 nm 535 nm Photostationarystate reached in 12s with 81% of ring closed isomer Reverts to open ring isomer after irradiation with visible light for 5 min Lemieux, V.; Spantulescu, M. D.; Baldridge, Kim K.; Branda, Neil R. Angew. Chem., Int. Ed. 2008, 47,

42 Calculated LUMO of Simplified Model Node H B O O Lower in energy by 19 Kcal/mol Node at the B H S S H Available p-orbital Lewis acidic Lemieux, V.; Spantulescu, M. D.; Baldridge, Kim K.; Branda, Neil R. Angew. Chem., Int. Ed. 2008, 47,

43 Probing Lewis Acidity with Pyridine Followed by 1 H NMR 1 H NMR δwill not change δ= 8.1 ppm 1 H NMR δwill shift OFF ON Open ring isomer will not bind to pyridine Closed ring isomer has Lewis acid reactivity in the presence of pyridine (Lewis base) Lemieux, V.; Spantulescu, M. D.; Baldridge, Kim K.; Branda, Neil R. Angew. Chem., Int. Ed. 2008, 47,

44 Binding of Closed Ring Isomer to Pyridine H NMR 8.05 Lewis Acidity : ON 1 H NMR Chemical Shift (ppm) Equivalents of Pyridine Ring Closed Isomer Binds with pyridine Chemical shift decreases upon binding 1 H δconsistent with 1:1 stoichiometry Lemieux, V.; Spantulescu, M. D.; Baldridge, Kim K.; Branda, Neil R. Angew. Chem., Int. Ed. 2008, 47,

45 Summary Acids and bases were given the ability to be turned on and turned off by attaching a molecular switch. Azobenzeneand dithienylethenewere shown to be effective at photoswitching acidity and basicity. The applications of photoswitchableacids and bases are yet to be explored.

46 Dr. Baker Qin, Sampa, Hui, Tom Dr. Jackson Dr. Hecth Dr. Blanchard Dr. Wulff Babak Karrie, Luis S., Wynter, Heyi, Yiding, Wen, QuanXuan, Scott Acknowledgements