E/Z Isomerization in Crystals—Phase Rebuilding on Photolysis with Long‐Wavelength Radiation

Abstract

I 1 J The g tensors and linewidths vary slightly for different samples. A representative EPR spectrum gives g , = 2.26, g,, = 2.02 (solid-state at 77 K). H,,,0.32x0.04x0.04mm3, hexagonal, P6,22, a = b =12.1121(5), c =17.3157(10),&, V = 2199.9(2) A3, 2 = 6, psalcd = 1.800 g~m -~, Mo,,radiation ( ; . = 0.71073 A), p = 1.22 mm-'. Data were collected on a Siemens CCD Smart system in the range 4<20< 54". 11859 measured reflections, 1625 unique, 1276 with F,40(F,) were used to refine 98 parameters to R(wR) = 0.0479(0.0786), GOF = 1.185; F Z refinement in SHELXTL 5.0. A $J scan absorption correction gave min. and max. transmission factors of 0.79 and 0 91. The highest peak in the final difference map = 0.527 e k ' . Crystallographic data (excluding structure factors) for the structure reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publlcation no. CCDC-179.110. Copies of the data can be obtained free ofcharge on application to The Director,CCDC, 12Union Road,CambridgeCB21EZ,UK(fax: 1nt.code +(1223) 336-033; e-mail: teched@chemcrys.cam.ac uk). [14] a) The tight binding band structure calculations used an extended Huckel-type Hamiltonian: R. Hoffmann, J Chem. Phys. 1963, 39, 1397. b) A modified Wolfsberg-Helmholz formula was used to evaluate the nondiagonal H,, values: J. Ammeter, H.-B. Biirgi, J. Thibeault, R. Hoffmann, J Am. Chem. SOC. 1978,100,3686. c) The exponents and parameters used were taken from R. H. Summerville, R. Hoffmann, L Am. Chem. Soc. 1976, 98, 7240. I151 M.-H. Whangbo, R. Hoffmann, J Am. Chem. Soc. 1978, 100.6093, [16] Preliminary data support a localized system as a result of strong electron correlation effects in one dimension. Application of pressure (ca. 25 kbar) is expected to restore metallic character (room temperature conductivity = 2 Scm-'):

Surface and Bulk Effects in Photochemical Reactions and Photomechanical Effects in Dynamic Molecular Crystals

“…Kaupp and Haak showed that Z-BDHF can isomerize to E-BDHF in a crystal-to-crystal process. 42 Desiraju and Kearsley noted that upon exposure to UV light for several hours crystals of E-BDHF bend and crack, but did not investigate the origin of these observations further. 43 Our own assessment of the reactivity of single crystals of BDHF exposed to UV excitation revealed highly incongruous mechanical response: while some crystals did not display any visible motility even at high excitation powers, others bent rapidly or burst violently.…”

Organic Solid-State Reactions with 100% Yield

“…are known with the reactions of 83 to give 84 (selective irradiation at 365 nm; photodimers of 84 occur at l>300 nm irradiation) [49]), 85 to give 86 [50] (the product lattice is interlocked [1]), 87 (P2 1 /c) to give 88 (P2 1 ) (EAEZ; the bent product molecules 88 pack in crossing mono-and bilayers with interlocked stacks [51]), and 89 to give 90 (neat or acetone complex; T<-15°C; colloidal particles formed in a macroscopically unchanged crystal [52]) (Scheme 7). The reactions of 83, 87, and 89 have been studied by AFM.…”

“…Most of the E/Z isomerizations in the solid state have been photochemically observed [48], but mostly not as uniform quantitative reactions. If these isomerizations cannot be performed under selective conditions of irradiation (an exception is 83/84) [49], the only chance to have these reactions uniform with 100% yield is a very efficient isomerization (according to the phase rebuilding mechanism) that leads to an isomeric product with heavily interlocked crystal lattice. Under such circumstances side reactions of the substrate and photoconversions of the product are prohibited (including the back reaction, of course).…”

Organic Solid-State Reactions

“…The cis-2-benzylidenebutyrolactone gives the trans-isomer upon irradiation with 365 nm light to avoid product absorption [18,117]. Both a rotational and a "hula-twist" mechanism can be modeled from the crystal packing.…”