Publication date: 28th June 2024
In this talk I will present our research activities using a vibrational probe to understand the effect of structure and interactions between molecules on the photophysical behavior of a conjugated polyelectrolyte. Resonance Raman spectroscopy can provide ground state information on the conformation of conjugated polymers under various environmental conditions, be it either temperature, solvent processing conditions, the film matrix, or under various chemical modifications. However, the intensity of the Raman bands in a resonant experiment contains rich information that has been underexplored in organic electronics. I will show how we employ the tools provided by this spectroscopic method to understand the sequence-dependent templating effect of single-stranded DNAs (ssDNAs) on the conformation of conjugated polyelectrolytes and consequently on the photophysical properties and excited state dynamics of a class of cationic polythiophenes (CPT) originally designed as a biosensor for detecting infection and genetic diseases. [1] Combining the selectivity provided by resonance Raman for a particular chromophore we were able to understand the interactions between a CPT and different ssDNAs that lead to particular templated conformations of the polymer. [2] Resonance Raman intensity analysis then provided insights on the excited state vibrational-mode-dependent reorganization as a function of the extent of interactions between the polymer and the ssDNA. Finally, we combined this information with ultrafast transient absorption experiments in the near- and mid-IR to understand the effect of structural templating on the excited state processes. [3] We found that while certain ssDNA sequences can induce order in the conjugated polymer backbone through extensive interactions between the two partners in the complex, the templating scaffold does not seem to be a mere spectator but instead participates and affects the excited state behaviour. This is something that needs to be considered in the design of functional templated conjugated polyelectrolytes for their suitability for particular bioelectronic applications.