Polarons and excitons play a central role in the electronic, optical, and transport properties of molecular aggregates, thin films and crystals, semiconducting polymers, and hybrid organic-inorganic semiconductors. In such π-conjugated systems, charged (polarons) and neutral (excitons) excitations are strongly coupled to the nuclear degrees of freedom, underscoring the importance of electron-phonon interactions. In the first half of my talk, I will present a theory describing the spatial coherence length of polarons in disordered organic materials, revealing a simple relationship between the oscillator strength of the infrared absorption band and the polaron coherence function. TheHolstein-type Hamiltonian, represented in a multiparticle basis set, has been successful in quantitatively reproducing several recently measured spectra recorded in doped and undoped polymer films, confirming the association of an enhanced peak ratio with extended polaron coherence. Emphasis will be placed on understanding the fundamental nature and origin of the components polarized along the intra and inter-chain directions and their dependence on structural and conformational disorder, vibronic coupling, and Coulomb binding. In the second half of my talk, we will explore the similarities and differences in the spectral response of excitons and polarons in organic materials, with a particular focus on how simple optical probes like steady-state absorption and photoluminescence can be used to extract information about the exciton and polaron coherence lengths -quantities which are critical for understanding nanoscale energy and charge transport processes in emergent semiconducting materials.

https://drive.google.com/file/d/1NXbalat41jJI4fLdyKG747WsoLs0bzi8/view?usp=sharing