1 research outputs found
Pyridalthiadiazole-Based Narrow Band Gap Chromophores
π-Conjugated materials containing pyridal[2,1,3]thiadiazole
(PT) units have recently achieved record power conversion efficiencies
of 6.7% in solution-processed, molecular bulk-heterojunction (BHJ)
organic photovoltaics. Recognizing the importance of this new class
of molecular systems and with the aim of establishing a more concrete
path forward to predict improvements in desirable solid-state properties,
we set out to systematically alter the molecular framework and evaluate
structure–property relationships. Thus, the synthesis and properties
of 13 structurally related D<sup>1</sup>-PT-D<sup>2</sup>-PT-D<sup>1</sup> compounds, where D represents a relatively electron-rich
aromatic segment compared to PT, are provided. Physical properties
were examined using a combination of absorption spectroscopy, cyclic
voltammetry, thermal gravimetric analysis, differential scanning calorimetry,
and solubility analysis. Changes to end-capping D<sup>1</sup> units
allowed for fine control over electronic energy levels both in solution
and in the bulk. Substitution of different alkyl chains on D<sup>2</sup> gives rise to controllable melting and crystallization temperatures
and tailored solubility. Alterations to the core donor D<sup>2</sup> lead to readily identifiable changes in all properties studied.
Finally, the regiochemistry of the pyridal N-atom in the PT heterocycle
was investigated. The tailoring of structures via subtle structural
modifications in the presented molecular series highlights the simplicity
of accessing this chromophore architecture. Examination of the resulting
materials properties relevant for device fabrication sets forth which
can be readily predicted by consideration of molecular structure and
which lack a systematic understanding. Guidelines can be proposed
for the design of new molecular frameworks with the possibility of
outperforming the current state of the art OPV performance