Thermally activated motion of cold excitons in conjugated polymers

• Published in: International journal of quantum chemistry 2023-05, Vol.123 (10), p.n/a
• Main Authors: Köse, Muhammet Erkan, Köse, Esra
• Format: Article
• Language: English
• Subjects: Activation energy; Chemistry; energy transfer; exciton; Excitons; Harmonic oscillators; Hopping (motion); Monte‐Carlo simulation; Organic light emitting diodes; Physical chemistry; Polyacetylene; Polymers; Polythiophene; quantum mechanical calculations; Quantum physics; Room temperature; Thermal energy; Vibration mode
• ISSN: 0020-7608; 1097-461X
• DOI: 10.1002/qua.27088

Thermally activated migration of localized cold excitons were investigated in archetypal conjugated polymers; trans‐polyacetylene, polythiophene, and poly(p‐phenylene vinylene). Room temperature thermal energy has been found to provide sufficient energy to avail substantial mobility for excitons. A simple undistorted but displaced harmonic oscillator model has been assumed to predict the activation energy for exciton hopping between identical sites in perfectly planar conjugated chains, promoted by vibrational modes with Bu symmetry. The activation energies of exciton hopping has been found to increase in the order of trans‐polyacetylene (6.4 meV), polythiophene (29.5 meV), and poly(p‐phenylene vinylene) (147.4 meV). A rough Monte‐Carlo simulation based on incoherent hopping mechanism reveals excitons can displace in an average of 2.17 nm in polythiophene whereas those distances are much smaller in poly(p‐phenylene vinylene) (0.24 nm) and trans‐polyacetylene (0.37 nm). The simulation results partially explain why polythiophene based polymers are better suited for organic photovoltaic applications whereas poly(p‐phenylene vinylene) are more appropriate for organic light emitting diode applications. Thermally activated diffusion dynamics of relaxed excitons were investigated theoretically. The activation energies of exciton migration were determined for commonly used conjugated polymers. The cold excitons are found to migrate significant distances over polythiophene backbone whereas such migration is much more limited in poly(p‐phenylene vinylene) chains due to high energetic barrier for diffusion. The results shed a light on why some conjugated polymers are better suited for specific optoelectronic applications.