CAS: Achieving Long Lived Charge Separated States in Donor-Bridge-Acceptor Dyads Based on 3d Alkynyls – a Synthetic Approach

With funding from the Chemical Synthesis program in the Division of Chemistry, Professor Tong Ren at Purdue University will prepare conjugated metal complexes of interesting photo-activity based on earth abundant metals. Chemists and material scientists have made great stride in molecular photovoltaics using so called dye-sensitized solar cells. The key molecules for the initial capture of solar energy are all based on rare precious metals such as Ru and Ir.

Hence, it is highly desirable to develop molecules of similar capturing capability but based on earth abundant metals such as Cr, Fe and Co. However, most of compounds based on earth abundant metals lose the captured solar energy (so called excited state) before converting it into electricity. Professor Ren and his coworkers will extend the lifetime of excited states by using a new family of macrocycles to support Fe and Co containing molecules, and hence improve the conversion efficiency of solar energy to electricity.

Professor Ren will work with a group of graduate and undergraduate students from diverse backgrounds. Through Purdue Science Express, he and his students will strive to improve the high school STEM education in the rural areas in Indiana through sharing laboratory equipment sets and designing new laboratory curriculum.

The chemistry of metal alkynyls is a vibrant and evolving field, on which important technological advances including photovoltaics, photo-catalysis and molecular electronic devices have been achieved. This project will seek to develop unsymmetric bis-alkynyl complexes with long lived charge separated excited states based on the combination of earth abundant 3d metals and unsaturated [14]-tetraene-N4 macrocycles.

The initial effort will be directed at the identification/preparation of suitable M([14]-tetraene-N4) starting materials, where M is Co(III) or Fe(III) and L is one of the three [14]-tetraene-N4 macrocycles, HMTI, TIM and TMTI. The ensuing effort will be focused on both the development of high yield preparation of the D-B-A dyads, and the understanding of donor/acceptor properties through voltammetry, steady state emission spectroscopy and ground state DFT calculations.

The later phase of the project will be focused on the dynamics of the excited states. Through collaborations, significant aspects include the temporal and spatial evolution of the MLCT states in [M(II)( [14]-tetraene-N4)] complexes will be studied using fs M-edge XANES technique and companion high level CASSCF/CASPT2 analysis; and the dynamics of photo-induced electron transfer with the D-B-A dyad using both pump-probe and time-resolved IR techniques.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.