Spectroscopic analysis of electronic energy transfer in molecular cassettes formed around boron dipyrromethene dyes

PhD ThesisPhotosynthesis, in its many diverse forms, has provided inspiration for countless researchers over several centuries and continues to spring surprises and new concepts. At the simplest level, photosynthesis can be considered to store sunlight in the form of chemical (or electrochemical) potential. As such, it is often proposed as a model for artificial systems aimed at the conversion and storage of solar energy. One of many key components of photosynthesis concerns the collection of sunlight by various pigments and the transfer of the resultant exciton to a reaction centre, where fuel formation can take place. In this thesis, we examine chemical systems that facilitate electronic energy transfer (EET) between chromophores arranged in rather simple molecular architectures built around boron dipyrromethene (Bodipy) dyes. These latter compounds are taken from an ever-expanding family of robust, highly fluorescent synthetic reagents developed originally as laser dyes and bio-labels. Chapter 1 gives a brief introduction to the general field of EET and covers a few basic concepts special to the photosynthetic apparatus. This is followed by a brief consideration of Förster theory, which is the staple mechanism underpinning much of the work covered in later chapters, and mention of the alternative Dexter theory for EET. By way of acknowledging that we are not the only researchers to explore this type of work, we provide a few key examples of molecular systems designed to probe various aspects of intramolecular EET. These examples cover Bodipy-based arrays and certain bio-inspired molecular systems. In Chapter 2, we describe the behaviour of certain sterically unhindered Bodipy dyes as fluorescent probes for rheology changes, most notably variations in viscosity under ambient conditions. This situation depends on changing the degree of (micro) friction between an appended meso-aryl ring and the surrounding medium. In order to vary in a systematic manner the resistance to gyration of the aryl ring, the photophysical properties of the dye have been recorded in different media and as functions of temperature and pressure. Local viscosity is also affected by the presence of an inert polymer. Extending the system to include an unusual bichromophore where the linkage is through boron-oxygen bonds switches off the sensory action due to light-induced electron transfer. Chapter 3 includes a critical comparison of EET within two disparate molecular types; namely, covalently-linked and non-covalently-linked molecular dyads bearing ii identical subunits drawn from the Bodipy family. Here, the intention is to explore how the binding motif affects the likelihood of intramolecular EET between the subunits. Both systems, which consist of a yellow Bodipy dye as a donor and a blue Bodipy dye as the complementary acceptor, show highly efficient EET. Again, the probability of EET has been probed as a function of applied pressure and temperature to better expose the mechanism. The non-covalently-linked system, which makes use of electrostatic binding between charged species, forms a liquid crystalline state upon heating and it is notable that efficacious EET occurs within this phase. Chapter 4 looks at the nano-mechanical properties of molecular-scale bridges in linear donor-spacer-acceptor compounds by monitoring the probability of intramolecular EET as a function of bridge length. The bridge (or spacer) consists of 1 to 5 ethynylene-carborane units that allow the centre-to-centre distance between the donor and acceptor to be varied systematically from 38 to 115 Å. Interestingly, the probability of EET is higher than the predicted value for all systems except the shortest bridge. On cooling to 77K, the agreement between theory and experiment agrees much better but depends on applied pressure in fluid solution at room temperature. We rationalise these various results in terms of structural distortion of the longer bridges, thereby allowing determination of the strain energy and Young’s modulus for the spacer unit. In Chapter 5, we report on a study of intramolecular EET in a molecular triad where the highest-energy donor is situated in the centre and there are two disparate Bodipy at the terminals. Overall, the probability of EET exceeds 95% and the individual EET steps can be resolved; the rate of EET follows the order of spectral overlap integrals. By selective protonation of one of the Bodipy-based terminals, it is possible to change the relative ordering of the spectral overlap integrals and thereby switch the direction of EET. This chapter also includes an investigation of the general photophysical behaviour of the symmetric triads, where the same Bodipy dye is present at each terminal, in addition to the spectroscopic properties of the isolated chromophores. Experimental variations include changes in solvent polarity, effect of lowing the temperature, moving from fluid to solid phases and applying high pressure to the fluid medium are discussed in this chapter. Finally, Chapter 6 provides a brief summary of the experimental approaches used throughout the work, including instrumentation and chemicals. In addition, the many mathematical equations and computer programs employed are mentioned here.King AbdulAziz University as represented through the Saudi Embassy for providing scholarship funds and the financial support

A numerical study of heat and momentum transfer over a bank of flat tubes

The present study considers steady laminar two-dimensional incompressible flow over both in-line and staggered flat tube bundles used in heat exchanger applications. The effects of various independent parameters, such as Reynolds number (Re), Prandtl number (Pr), length ratio (L/Da), and height ratio (H/Da), on the pressure drop and heat transfer were studied. A finite volume based FORTRAN code was developed to solve the governing equations. The scalar and velocity variables were stored at staggered grid locations. Scalar variables (pressure and temperature) and all thermophysical properties were stored at the main grid location and velocities were stored at the control volume faces. The solution to a one-dimensional convection diffusion equation was represented by the power law. The locations of grid points were generated by the algebraic grid generation technique. The curvilinear velocity and pressure fields were linked by the Semi-Implicit Method for Pressure Linked Equations (SIMPLE) algorithm. The line-by-line method, which is a combination of the Tri-Diagonal Matrix Algorithm (TDMA) and the Gauss-Seidel procedure, was used to solve the resulting set of discretization equations. The result of the study established that the flow is observed to attain a periodically fully developed profile downstream of the fourth module. The strength increases and the size of the recirculation gets larger as the Reynolds number increases. As the height ratio increases, the strength and size of the recirculation decreases because the flow has enough space to expand through the tube passages. The increase in length ratio does not significantly impact the strength and size of the recirculation. The non-dimesionalized pressure drop monotonically decreased with an increase in the Reynolds number. In general, the module average Nusselt number increases with an increase in the Reynolds number. The results at Pr = 7.0 indicate a significant increase in the computed module average Nusselt number when compared to those for Pr = 0.7. The overall performance of in-line configuration for lower height ratio (H/Da = 2) and higher length ratio (L/Da = 6) is preferable since it provides higher heat transfer rate for all Reynolds numbers except for the lowest Re value of 25. As expected the staggered configurations perform better than the in-line configuration from the heat transfer point of view

A review of floating photovoltaic installations: 2007 2013

[EN] The paper gives a review of the various projects that have been realised in throughout the years. These have all been in enclosed water bodies such as reservoirs, ponds and small lakes. The main motivation for the floating photovoltaic (PV) panels was the land premium, especially for agricultural sites were the land was more valuable for growth of the crops (in these cases, grapes because the sites were wineries). The PV panels of the existing projects are mounted on a rigid pontoon structure and vary between horizontal and tilted installations. Future concepts proposed for marine and large lacusterine sites are envisaged to incorporate laminated thin film PV, which would allow the structure to be flexible and able to yield with the oncoming waves, and submergible arrays, which would be submerged in harsh weather conditions. Interest and research has been developing in this niche field throughout the years and has currently reached the megawatt scale with even bigger plans for the future. Copyright (c) 2014 John Wiley & Sons, Ltd.The author acknowledges the co-operation of Prof. Marco Rosa-Clot from Scienza Industria Technologia (SCINTEC), Dr. Miguel Redon Santafe from the Polytechnic University of Valencia, SPG Solar, Pontili Gallegianti, and Dr. Yuzuru Ueda from the Tokyo Institute of Technology in collaboration with the Japan National Institute of Advanced Industrial Science and Technology in providing photographic images of the projects and also details about the installations. The author also would like to acknowledge the support given by MIRARCO in funding their on-going research in floating photovoltaics.Trapani, K.; Redón-Santafé, M. (2015). A review of floating photovoltaic installations: 2007 2013. Progress in Photovoltaics. 23(4):524-532. doi:10.1002/pip.2466S52453223

A Global Collaborative Effort to Enhance Design in a Mechanical Engineering Curriculum in Saudi Arabia

In 2008, King Fahd University of Petroleum and Minerals (KFUPM) in Saudi Arabia and the Massachusetts Institute of Technology (MIT) partnered together to develop project-based curricular material to be tested out in a new undergraduate course offering in KFUPM’s Department of Mechanical Engineering. This paper details some of the unique challenges to collaborating across countries and time zones, and the approaches the KFUPM-MIT team used to address these. These approaches have so far included the establishment of a shared vision for the project and the use of an array of technologies to facilitate distance communication. The paper concludes with a description of lessons learned that might be useful for future programs that plan to engage in international collaboration on design education.Jāmiʻat al-Malik Fahd lil-Batrūl wa-al-Maʻādi

A coupled optical-thermal-electrical model to predict the performance of hybrid PV/T-CCPC roof-top systems

A crossed compound parabolic concentrator (CCPC) is applied into a photovoltaic/thermal (PV/T) hybrid solar collector, i.e. concentrating PV/T (CPV/T) collector, to develop new hybrid roof-top CPV/T systems. However, to optimise the system configuration and operational parameters as well as to predict their performances, a coupled optical, thermal and electrical model is essential. We establish this model by integrating a number of submodels sourced from literature as well as from our recent work on incidence-dependent optical efficiency, six-parameter electrical model and scaling law for outdoor conditions. With the model, electrical performance and cell temperature are predicted on specific days for the roof-top systems installed in Glasgow, Penryn and Jaen. Results obtained by the proposed model reasonably agree with monitored data and it is also clarified that the systems operate under off-optimal operating condition. Long-term electric performance of the CPV/T systems is estimated as well. In addition, effects of transient terms in heat transfer and diffuse solar irradiance on electric energy are identified and discussed

Numerical simulation of lid driven flow in a curved corrugated porous cavity filled with CuO-water in the presence of heat generation/absorption

In this article, numerical simulation is performed for mixed convection lid-driven flow of CuO-water nanofluid enclosed in a curved corrugated. Cylindrical obstacles having three different constraints: (adiabatic, cold, and heated) at its surface are considered. Internal heat generation/absorption and uniform heat is provided at the vertical wall of the cavity. The bottom wall is insulated, and the curve surfaces are maintained with cold temperature. Mathematically equations are developed from physical problems and solved through Galerkin weighted residual method of FEM formulation. The effect of various Reynold number (), Darcy number (), solid volume fraction of nanoparticles (), heat generation/absorption coefficient () and various cylindrical obstacle on velocity, Nusselt number, molecular movements and the flow structure has been studied. Nusselt number increases for high Darcy number due to the convection in lid cavity. For high Reynold number generally Nusselt numbers decrease or remain the same at the wall with an increase of nanoparticles in porous medium. There significant effect of heat sink coefficient on temperature profile and Nusselt number decreases with increasing of Q

Multiple nonlinear regression model for predicting the optical performances of dielectric crossed compound parabolic concentrator (dCCPC)

As a typical type of three-dimensional compound parabolic concentrator (CPC), dielectric crossed compound parabolic concentrator (dCCPC) has drawn a significant research attention in these years to explore its angular characteristics in solar collection for concentrating photovoltaics and daylighting control in buildings. Optical efficiency and transmittance are the main performance indicators to evaluate a dCCPC which may be base-coated as a receiver or non-coated for daylighting. The most common way to accurately determine the performance of a dCCPC is through ray-tracing simulation which requires advanced optical analysis software and lots of time. To facilitate the annual performance evaluation of dCCPC, this study puts forward several mathematical models for multiple nonlinear regression based on a mass of simulation results. The models can predict the transmittance of non-coated dCCPC and the both of transmittance and optical efficiency of base-coated dCCPC from several sky parameters, respectively. The agreement between predicted and simulated values is generally satisfactory. The coefficient of determination (R2) for each model is higher than 0.94 and the mean square error (MSE) is less than 0.002. Six specific time among the whole year are selected to verify the reliability of the prediction models in practice. The limitation and significance of these models are discussed as well. The regression models provide a convenient and accurate approach to predict the optical performance of dCCPC