Matrix-isolation, photochemistry, and spectroscopy of benzothienyl diazo compounds

Photolysis of matrix-isolated 3-thienyl diazomethane generates triplet s-Z and s-E-3-thienyl carbene, which is characterized by IR, UV-vis, and EPR spectroscopy. The EPR spectrum of the triplet carbene proved unusual, and so a variety of NBO and spin density calculations, as well as simulations of the spectra were carried out to better understand the experimental findings. (Chapter 4) To build on previous work, the remainder of this work focused on the photochemistry and spectroscopy of the unsubstituted and methyl substituted 2- and 3-benzothienyl diazo compounds. While the methyl substituted 2-benzothienyl diazoethene was successful in generating the corresponding carbene, irradiation of 2-benzothienyl diazomethane under any conditions was unsuccessful in generating 2-benzothienyl carbene. Instead, 2-benzothienyl diazomethane opens up to a cyclic allene (irradiation at lambda > 534 nm) and a bicyclic cyclopropene (irradiation at lambda > 363 nm). Narrow band irradiation was carried out in an attempt to convert the cyclic allene to either 2- or 3-benzothienyl carbene, however these attempts were unsuccessful. (Chapter 1).;3-Benzothienyl diazomethane was matrix isolated and its photochemistry explored. The photochemistry of the benzannulated compound mirrored that of the parent 3-thienyl diazomethane, except that no triplet carbene was detected. Upon irradiation (lambda > 472 nm) the diazo compound is converted to a bicyclic cyclopropene, which, at lambda = 340 nm opens to give a mixture of E- and Z-vinyl acetylene thiones as well as a cyclopropene thione. This cyclopropene thione is a deep purple color, due to its aromatic charge-transfer character. Further irradiation at lambda = 300 converts some of the acetylenic species to the same cyclic allene observed upon irradiation of 2-benzothienyl diazomethane. (Chapter 2).;The last member of this family, 1-(3-benzothienyl) diazoethane, was successful in generating triplet 1-(3-benzothienyl) ethylidene upon irradiation at lambda > 571 nm as characterized by UV-vis and EPR spectroscopy. The EPR spectrum shows the same unusual characteristics as 3-thienyl carbene, with a large difference in D values between the s-E and s-Z rotamers of the carbene. Shorter wavelength irradiation (lambda > 472 nm) converts the carbenes to E- and Z-vinyl benzothiophene. (Chapter 3).