Advancing the State of Knowledge
RFA2 will develop the fundamental science of charge neutral, π-conjugated, macromolecular chemistries with tunable open-shell configurations. Organic macromolecules are particularly appealing candidates to replace and/or complement traditional semiconducting materials in devices and are being used as building blocks of new optoelectronic devices (organic thin film transistors, organic light-emitting diodes (OLEDs), solar cells, and photonic devices). Non-linear optics, where optical properties of materials depend on the intensity of light, is one such example where there is an intense research effort currently underway. However, to realize this immense potential, we need to have a better understanding of how molecular structures (motifs) alter the electronic structure of macromolecules. This RFA utilizes exhaustive and detailed computational and state-of-the-art characterization tools to pin down structure property relationships to establish design rules for identifying molecular features for specific optoelectronic applications. One of the unifying theoretical concepts at the heart of these properties is the diradical character (which is a measure of the degree of open-shell character (unpaired electrons) see RFA2 Overview Figure).
The RFA2 effort will afford the rational development of materials with complex and tunable electronic structures, varying magnitudes of intramolecular electron-electron pairing, cooperative electronic properties based on π-electrons, and controlled spin alignments; design paradigms which underlie the development of next generation optoelectronic technologies. Synthetic control of these features will impart varying degrees of, and distinct, optical, electronic, spin, magnetic, transient, and multifunctional activities not possible with other semiconductor materials. Research objectives and tasks (defined below) have been developed to address the following research questions:
2.1 What are the molecular, electronic, and solid-state requirements for the adaptation of various ground state (GS) electronic configurations (aromatic, quinoidal, biradicaloid, polyradicaloid, high-spin)? How can these be applied to diverse materials systems?
2.2 What factors govern the magnitude of intramolecular electron-electron pairing in тт-extended biradicaloids and lead to unique optical, NLO electrical, transient, spin, and magnetic properties?
2.3 How do we control spin alignments and manipulate the energies between these states to access truly stable, high spin OSCs? Is the total spin (S) a function of systems with more than two “sites” for unpaired electrons and what effect will radical delocalization have on spin coupling (J) in extended systems? To what extent can J be tuned? How do we use anisotropic, hierarchical, and supramolecular structures to influence S and J?
2.4 What new phenomena and properties are available, to what degree can they be controlled, and how can they be translated into devices?
2.5 Can powerful computational approaches be developed, through experimental benchmarking, to make use of the collective properties of conjugated тт-electrons as a design paradigm to access long range electronic, structural, magnetic, excited, coherent, and quantum states?
Goals and Objectives
Goal 2: Synthesize charge neutral, pi-conjugated, macromolecular chemistries with tunable open-shell configurations and establish theoretical basis for predicting properties
Objective 2.1: Establish design rules for pi-extended open-shell organic macromolecular systems
Objective 2.2: Quantify the role of diradical index on photophysical, electrical, magnetic, and spin properties