(376bn) Design and Analysis of High-Spin Ground State Donor-Acceptor (DA) Polymers: A Computational Study

There have been a lot of efforts to design new types of organic materials having a high-spin state that can be a replacement of traditional silicon-based materials used in semiconductor, light-emitting-diodes, photovoltaics, and solar cells. Polymeric materials having alternating donor-acceptor (DA) units are under intensive study due to its solution processability, backbone flexibility, light-weight and low processing cost than silicon-based materials. For years, stable high-spin state DA polymers have been elusive to the scientific community. High-spin state organic molecules have drawn intensive interest in the field of organic chemistry as well as in materials science. Although, the unpaired electrons in high-spin molecules exert exotic properties, however, their design and characterization have confounded the scientific community due to the intrinsic instability of these molecules. Computational modelling can be used to design new types of molecules and study their properties in depth. Here, we report the design and characterization of two new donor-acceptor (DA) polymers, which have degeneracy (ΔE_ST=0) between the singlet (S=0) and triplet (S=1) states in the neutral form. Large separation between the unpaired electrons both in singlet and triplet states with a pure diradical character (y=1.0) proves that polymers have a high tendency to be in a triplet (S=1) state for longer chain lengths. This study shows the possibility to synthesize new DA polymers, which are stable at ambient conditions, with intriguing molecular and electronic properties.