Probing H- and J- aggregate spectral signatures via Stokes formalism for polarized light: applications to P3HT

Spectroscopic measurements, particularly PL (and subsequently absorption measurements) have seen significant use as a means of probing H- and J- aggregate behavior in P3HT among other polymer systems. While excitonic transitions associated with these aggregate formations are readily obtained and visualized at low temperature (T<70K), thermal affects broaden their spectral signatures, making it difficult to accurately resolve signatures of one transition to another. Modeling, including Frank Condon fitting and numerical calculations have been able to deconvolute peaks from PL signatures, even from high temperature data (T>150K). However, these fitting techniques involve in depth fitting algorithms and don’t necessarily interact directly with acquired PL signatures, instead providing best fit approximations. Here, we show how the Stokes Formalism can be applied to acquire polarization dependent spectroscopic emission, and that the off axis linear polarization shows heightened resolution of aggregate emissions typically unresolvable at high temperature (T>150K). Subsequent analysis of this polarized emission is then used following proposed theory to obtain emission peak rations, coherence lengths, coherence numbers among other pertinent parameters.