Electron-transfer Photoinduced From Naphtholate Anions - Anion Oxidation Potentials and Use of Marcus Free-energy Relationships

The fluorescing excited states of four naphtholate type anions are quenched by various acceptors according to an electron-transfer mechanism. By use of the Marcus free energy relationship, the electron-transfer rate constants were correlated with the reduction potentials of the acceptors and a first set of oxidation potentials (around 0.5 V) was estimated for the anions. The fluorescence of perylene was quenched by the naphtholate anions but a second set of oxidation potentials, different from the preceeding one was obtained for the anions (around 1 V). The difference was rationalized by considering that a hydrogen bond between the anion and the solvent is broken during the excitation when the anions are in their excited states. The hydrogen bond is broken during the electron-transfer quenching when the naphtholate anions are in their ground states. This implies, in the first case, an intrinsic activation barrier, taking the H bond rupture into account. In the second case, the fraction of the excitation energy available for electron transfer must be evaluated. The oxidation potentials after correction were finally estimated around 0.8 V. In DMF, the oxidation potential of the 2-naphtholate anion is found to be decreased (around 0.1 V) and this is probably related to the lack of any hydrogen bonding in this solvent. The use of the Marcus model and the possibility of measuring in the inverted Marcus region are discussed

Structural Glazing: Design under High Windload

Bonding of glass onto aluminum frames, known as “Structural Silicone Glazing”, has been applied for more than 40 years in glass curtain wall facades. Silicone sealants are being used in this application because of their outstanding resistance to weathering (UV, temperature, moisture, ozone), They also provide resistance to water egress and thermal insulation. Their role, structurally, is to resist to windloads and to compensate for differential thermal expansion of glass and aluminum frame. For windload resistance, silicone bite is calculated using a simplified equation which assumes a uniform stress distribution along the sealant bite. Finite Element Analysis (FEA) was used in this study calculate the stress distribution in the sealant as a function of sealant bite and thickness and show the importance of the sealant geometry (bite and thickness) on the local stress distribution. The study shows that for glass deflections in the 1% region (L/d=100), large sealant joints and/or high modulus sealants lead to higher local stresses