Surface photochemistry: Semiconductor mediated reactions of some saturated strained hydrocarbons

Abstract

Quadricyclane (1) and 1,8-bishomocubane (2) have been found to undergo valence isomerization to norbornadiene and tricycl0[4.2.2.0~.~]deca-3,7-diene, respectively, on illuminated CdS and ZnO. An electron transfer mechanism is proposed.Quantum yield, solvent effects, the role of oxygen, and the quenching of the reaction were investigated, and were consistent with this interpretation. The thermal reaction of 1 on CdS was also suggested to be an electron transfer process involving, in this case, defects or trapped holes on the surface of the semiconductor. An examination of a series of strained hydrocarbons structurally related to 1 (

Carbon tetrabromide as an electron acceptor in heterogeneous photocatalysis

“…Molecular oxygen has been found to enhance the rate of many semiconductor-mediated reactions (9)(10)(11)(12)(13)(14)(15)(16)(17). As an electron acceptor, adsorbed on the semiconductor surface, it traps the electron as superoxide ion.…”

Chelating the Surface of Zinc in Zinc Oxide Nanocrystals: Spectroscopic Characterization of ZnO Surface-Bound Eriochrome Black T and 8-Hydroxyquinoline

“…By understanding the features on the surface of ZnO NCs, which influence the observed luminescent changes, the sensory, catalytic, and electronic applications can be developed. − In this paper we have examined the binding character of two chromophoric chelating agents, HQ and ErT and their effect on the absorption and emission properties of ZnO NCs. The static binding of both of the chelates was inferred from quenching dynamics though Stern−Volmer analysis, and the binding constants determined to be K a = 2.52 × 10 −6 and 7.14 × 10 −6 M −1 for HQ and ErT, respectively.…”

“…The surface of semiconducting zinc oxide (ZnO) plays a large role in its optical, catalytic, and electronic properties. − In nanomaterials the importance of this surface increases tremendously due to the large surface to volume ratio, quantum confinement, and increasing relative quantity of the surface-related defects. ,,− Investigating the coordination geometries of zinc and oxygen on the surface of ZnO nanocrystals (NCs) would provide insight into surface related properties and effects of surface modification on the physiochemical properties of the nanomaterials. The surface structure of nanomaterials is difficult to assess, as most analytical methods represent an average of the surface properties .…”

Rh(III)-Photosensitized Interconversion of Norbornadiene and Quadricyclane

“…Triplet-sensitized irradiation of N results in clean and efficient conversion (φ ≈ 0.9) to the higher energy isomer Q . , The reversion of Q to N , with the liberation of the strain energy as heat, can be affected by transition metal catalysts. The conversion of Q to N may also be facilitated by one-electron oxidation, followed by valence isomerization of Q •+ to N •+ (eq 1). − Chemically induced dynamic nuclear polarization (CIDNP) studies have established the existence of Q •+ and N •+ as two distinct species and have provided indirect evidence for the valence isomerization reaction. − We recently reported the direct detection of Q •+ by time-resolved ESR and estimated the rate constant for the valence isomerization to N •+ ( k vi ≈ 10 6 s -1 ) …”

“…The conversion of Q to N may also be facilitated by one-electron oxidation, followed by valence isomerization of Q •+ to N •+ (eq 1). [4][5][6][7][8][9][10][11][12][13][14] Chemically induced dynamic nuclear polarization (CI-DNP) studies have established the existence of Q •+ and N •+ as two distinct species and have provided indirect evidence for the valence isomerization reaction. [15][16][17][18] We recently reported the direct detection of Q •+ by time-resolved ESR and estimated the rate constant for the valence isomerization to N •+ (k vi ≈ 10 6 s -1 ).…”