Supramolecular Photochemistry Controlling photochemical reactions through templatation Concept Examples In the absence of control photoaddition leads to multiple products > + f¥ fr & P • Multiple products with different stereo and regiochemistry possible (assuming no electronic or steric preference). • Pre-organization is essential to achieve selectivity. The cost for selectivity should be pre-paid, i.e., system should be entropically prepared B 2 Water Soluble Hosts as Confining Media Cyclodextrins Cucurbiturils Pd Nano Cage Calixarenes SDS / CTAC NaCh / NaDCh Dendrimers Octa acid 4 Concept of Reaction Cavity Reaction cavity Role of Weak Interactions van der Waals Charge transfer 6 Pre-organization Through Weak Interactions 7 Templation in solution through hydrogen bonding Host R Guest templated by host Temptation in solution through hydrogen bonding MeO XX, 2H R R COOMe O^X^_^O T O Me Me O B (R = hexyl) C Quantum yields of photodimers (x 0.001) dimers a a + 0.5 equiv of b a + 0.5 equiv of c d 0.7 2.3 0.7 e 0.1 0.6 0.1 f <0.1 0.8 <0.1 Ar Ar D X A AX Ar Ar E COOMe COOMe «e^Y^H H'NYYOMe C6H12 C6H12 ^COOM^cOOMe hv Ar Ar D Isomerization slowed; dimerization enhanced O O A X X 9 Templation in solution through hydrogen bonding C8H17 C8H17 h-nynyn + Interface helps to orient reactant molecules Outside Inside are the same Poor alignment Multiple products Homogeneous Systems: Solution, crystals • Water molecule Br" I TT TT TT TT Highly aligned Single products Microheterogeneous systems and some homogeneous systems : Silica, clay, zeolite surfaces, and monolayers, micelles, bilayers, organic, inorganic hosts and biological systems in water. 11 SDS C16 CTAB Temptation with the help of an organic host: Cyclodextrins Oligosaccharides consisting of 6 or more a-1,4-linked D-glucose units Volume (Ä3): 176 (a), 346 (ß), 510 (y) Dia at the larger end 8.8 (a), 10.8 (ß), 12.0 (y) 14 Temptation with the help of an inorganic host: Fujita pd host Size controlled inclusion. Interior dia ~ 30 A Interior hydrophobic Water soluble A H2 /x\ Or ■•»»/ NO2 - -► H2 O Ar = R-Ph hv - A^^COOCH3 A^sUCOOCH= syn H-H dimer + PjiO^COOCHa Substrate % of Syn H-H dimer % of cis isomer in nanocage O 63 37 45 55 H=C°V0.-VAOCH 3 42 58 O 40 60 16 Ri Syn HH Syn HT Anti HH Ri= R^2= R3=H Water Pd-nanocage 60 >90 40 - R1=Me, R2=R3=H Water Pd-nanocage 15 >90 - 85 R2= OMe, R1= R3=H Water Pd-nanocage >90 >90 - R3=OMe Water Not soluble r1=r2= h Pd-nanocage >90 - - Schmidt's generalization of solid state reactions hv a - form Double bond separation: 3.6 - 4.1Ao Nearest neighbour relation; Centric # - form (3.9 - 4.1Ao; Translation) % - form (4.7 - 5.1Ao; Translation) ft Ph COOH - TRUXILLIC ACID COOH COOH # - TRUXINIC ACID NO REACTION Topochemical principle: Reactions in the solid state take place with minimum atomic movements. 20 Ph Solid COOH trans-Cinnamic acids photo inactive in solid state (y-form) Crystals No Reaction hv Solution Ar = R-Ph CB[8] OcH3 CH3 Ar Solid state % of dimer in % of cis isomer CB[8] R=4-OCH3 -- 72 28 R=3-OCH3 -- 72 28 R=3-CH3 -- 83 17 trans-Cinnamic acids that yield anti H-T dimer upon irradiation in solid state (a-form) hv Crystals Solution HoocTs^Ar Ar = R-Ph CB[8] Ar So|id rtjrfe % of Syn H-H dimer % of cis isomer % of anti H-T dimer in CB[8] R=H R=4-OH R=4-NH3* 100 100 100 54 38 88 46 62 12 Photodimerization of trans-Cinnamic acids Ar hv COOH Solid hv IT Solution It Ar COOH a - form Double bond separation: 3.6 - 4.1A Nearest neighbour relation; Centric ß - form (3.9 - 4.1Ä; Translation) $ - form (4.7 - 5.1Ä; Translation) COOH Ar COOH - truxillic acid Ar COOH COOH ß - truxinic acid No reaction Topochemical principle: Reactions in the solid state take place with minimum atomic movements. G. M. J. Schmidt et al. 'Solid State Photochemitsry, A Collection of Papers, Verlag Chemie, 1976? a-trans-C\r\mm\c acid Leads to centrosymmetric dimer p-trans-Cinnamic acid Leads to mirror symmetric dimer 29 Templation through Cl—Cl interaction: Crystal engineering 30 Templation through Cl---Cl interaction 31 Templation through ionic interaction Ar Ar c NH3+ -OOC NH3+ -OOCV Ar = o-MeC6H4 Ar = o-ClC6H4 Ar = tm-NO2C6H4 Ar = 2-thienyl Ar Ar hu, Ar solid HO2C CO2H "-truxinic acid 30% 84 70 13 CO2H 23% 9 4 0 Temptation through hydrogen bonding 0 ,°-h-nQ>-V_ h-nO> 0 35 Templation through hydrogen bonding 0-c Thiourea as a Template: Importance of Hydrogen Bonding CSD entry: AMILIR CSD entry: AMILOX H \ 38 H2N H2N >= H2N S H2N >=° X = H, F, Cl, Br, Me, OMe and CN 39 O N Cl An overview of photochemistry of stilbazoles in thiourea co-crystals X = H X = F X = Cl X = Br X = CH3 X - H, F, Cl, Br, Me, OMe and CN ■1 .■ ■: .; -1 ■-. ::>. -2 PPM 1H NMR (CDCl3) of cyclobutane protons in dimer products Stilbazole not oriented suitably for photodimerization E. Cariati, D. Roberto, R. Ugo, V. I. Srdanov, S. Galli, P. Macchi, A. Sirom New J. Chem. 2002, 26, 13. Stilbazole + HCI 4-Halo Stilbazole.HCI Salt \ 3.691 A **\4.500 A Inter-planar distance = 3.416 A J Plane defined using the pyridyl ring 3.691 A Inter-planar distance = 3.569A NH 4-Halo Stilbazole.HCl Salt . 3.752 A \ 3.865 A 3.752 A Inter-planar distance = 3.489 A Inter-planar distance = 3.393A Cl NH Inter-planar distance = 3.553 A \- Inter-planar distance = 3.425A NH 47 3.768 A \ 3.807 A / 3.768 A Inter-planar distance = 3.537 A Plane defined using the pyridyl ring Inter-planar distance = 3.645A F3C NH \ 3.691 A **\4.500 A 3.691 A hv Anti H-T Dimer 48 F Weak interactions help orient molecules Cation—! bond O z X Hydrogen bond -ED —EA Charge transfer bond Chlorine—Chlorine ED = electron donor EA = electron acceptor Quadrupole—Quadrupole jt-jt bond