Tuning the electronic and optical properties of small conjugated organic molecules can lead to the development of wide range of applications in photonics, photovoltaics, organic solar cells and sensors. Herein, we investigate the optoelectronic properties of the oligomer units of the type D-A (donor-acceptor) and D-π-A based on donor (CPDT, cyclopentadithiophene), acceptor (BT, benzothiadiazole) and π-spacer (Pyrene and Perylene dimide (PDI)) molecules and extend the studies to envisage the electron dynamics and intramolecular charge transfer. Based on electronic structure calculations using density functional theory (DFT), we predict a significant change in the optical properties of these oligomer units. Our computations reveal that PDI based D-π-A shows a narrow band gap in the near IR region. The excitation studies and molecular orbital analysis discloses a possible charge transfer from HOMO to LUMO along D-π to A and D-π to π-A in CPDT-Pyrene-BT and CPDT-PDI-BT, respectively. Further, the CPDT-BT and CPDT-Pyrene-BT show photoluminescence in visible region while CPDT-PDI-BT in near IR region demonstrating a promising application in the organic semiconducting devices and solar cells. The transient excitation studies using real-time time dependent DFT demonstrates a temporal change in the electron density and fast electron processes providing robust insights among the D-A and D-π-A systems. The computed reorganization energies and charge transfer rates unveils high electron mobility with PDI π-spacer. Our study aims to pave the path for tuning the properties of D-A systems through a selective choice of the type and number of D, A and π spacers. This will aid the realization of optoelectronic devices with clean and affordable source of energy.

Optical properties and charge transfer in D-A and D-π-A oligomers

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.