Strong Photophysical Similarities between Conjugated Polymers and J-aggregates

The photophysical properties of emissive conjugated polymer (CP) chains are compared to those of linear J-aggregates. The two systems share many properties in common, including a red-shifted absorption spectrum with increasing chain/aggregate length, enhanced radiative decay rates (superradiance) relative to a single monomer/molecule, and several vibronic signatures involving the vinyl-stretching mode common to many conjugated molecules. In particular, the scaling of the 0-0/0-1 photoluminescence ratio and radiative decay rate with the inverse square root of temperature in red-phase polydiacetylene is also characteristic of linear, disorder-free J-aggregates. The strong photophysical resemblance is traced to the excitonic band structure; in one-dimensional direct band gap semiconductors as well as J-aggregates, the exciton band curvature is positive at the gamma point (k = 0).