Observation of strong electron-phonon interaction in polymeric diluted organic semiconductor

[Display omitted] Incorporating organic semiconductors in insulating polymer films, creating the so‐called diluted organic semiconductors, has been successfully used in different optoelectronic devices, including organic light-emitting diodes. However, the fundamental understanding of their excited state dynamics and spin physics remains elusive. Here, we present the temperature-dependent photoluminescence (PL) and transient absorption study of a model fluorescent organic dilute semiconductor where organic fluorophore pyrene is incorporated in the insulating Poly-methyl methacrylate (PMMA) polymeric backbone as pendant unit (py-PMMA). We observe that by lowering the temperature from 300 K to 140 K, the monomer fluorescence emission from py-PMMA gets blue-shifted, and their intensity enhances, which is attributed to less charge carrier scattering lattice sites at low temperature. Interestingly, we observe additional higher energy peaks at 368 nm (∼3.36 eV) below 70 K in fluorescence emission, explained by the exciton-phonon coupling. The exciton-phonon interaction constant (γph) is determined as 168 µeV/K, higher than other reported systems. The transient absorption measurement reveals the hot band relaxation (τ1 = 1.9 ps) and exciton- acoustic phonon interaction (τ2 = 27.2 ps) dominating in the excited state. Our study establishes that the electron–phonon interaction can play significant role in determining the optoelectronic properties of the fluorescent dilute organic semiconductor.