We investigate the photophysical, photochemical, and electrochemical behaviors of porous molecular assemblies. Our energy future greatly depends on the development of new strategies for efficient photonic energy conversions. For this, we need efficient (artificial) light-harvesting (LH) systems that can deliver the excited energy to appropriate sites to generate redox equivalents (charges with appropriate potential). Alternatively, such redox equivalents can be electrode injected. Nevertheless, these charges need to be propagated to relevant catalytic sites to drive chemical reactions or desired energy conversion (or storage) processes. These are orthogonal problems—highly conducting compositions have low bandgap to compromise the potential of the charges. Our research aims to design molecular assemblies such as porous metal-organic frameworks with optimum optoelectronic properties enabling unique photophysics suitable for better LH functionality as well as required charge transport properties. Currently, we are discovering how linker electronic structure, metal-linker bonding and coordination chemistry, and MOF topology provide a unique toolbox to tune the ground and excited-state electronic properties. We seek to apply these principles to energy conversions with better performance, materials stability, and product selectivity.
Photophysics of crystalline porous frameworks: Here we seek to develop a porous antenna where the optoelectronic properties of these solids can be tuned based on their structure. We have discovered that the excited states in MOFs are dispersed over multiple chromophoric linkers. We also established that the excitonic properties (energy, size, and dynamics) evolve as a function of MOF topology, which dictates the interlinker distance and orientation, and therefore excitonic interaction. The corollary is a new MOF design (based on new linkers and appropriate topological net) featuring efficient directional exciton propagation. Eventually, these excitons will be used to generate multiple excitons (fissions) and/or charge carriers at the appropriate sites.
Electrochemical properties of low-density porous molecular frameworks: Electrochemical behaviors of the redox-active species within the framework are unique: while the pores facilitate diffusion of solvent, substrates, and counter ions, the relative size becomes the key factor. Therefore, (variable) spatial constrain within the nanoscale pores can impart kinetic and reorganization energy requirements. For metal-carboxylate-based insulating MOFs, where the metal nodes provide a large electrochemical window, charge transport is hopping dominated and can be tuned by the topology. We have also discovered a strategy that improves charge transport upon substrate binding. For semiconducting MOFs, charge transport can be more-or-less tuned by engineering the metal-linker bonding and coordination chemistry. Depending on the need, appropriate dialing of these parameters can lead to efficient charge transport facilitating the electrocatalytic process.
Photochemical processes within the framework pore: The photophysical and electrochemical understandings can be leveraged to drive chemical transformations. We are poised to pick on various unique photochemistry that otherwise can be difficult to achieve in homogeneous solutions or solid aggregates. For example, multi-chromophore MOF antennas can be perfect to steam up a catalyst assembly through multi-electron redox activation. Such developments will circumvent common deactivation ‘traps’ (e.g., thermal collision and/or poor solubility -driven precipitation of catalyst intermediates –enroute its active state) seen both in light and electrode-driven catalytic processes. Likewise, MOFs can be the structural platform for selective transformations; especially beneficial for those where recycling expensive (or environmentally not so friendly) catalysts is challenging.
RECM (research experience with chromophores and MOFs) program for regional HS students: The educational outreach program is for regional high school students (>14 yrs age group) to provide hands-on experience on modern Chemical Science research and education. This program—beyond the usual classroom setup—is designed to generate interest and motivate young minds. The exposure to the modern research environment will provide opportunities to use exciting modern instrumentation to complete a small-scale, mentored science project (focusing on basic science and the prospect of a sustainable future). We invite regional HS students to spend 2-3 weeks (paid) in our laboratory to interact and perform scientific research. To participate please contact Dr. Deria (students from under-represented groups, as well as female students, are preferred).