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Yadagiri B, Kaswan RR, Tagare J, Kumar V, Rajesh MN, Singh SP, Karr PA, D'Souza F, Giribabu L. Excited Charge Separation in a π-Interacting Phenothiazine-Zinc Porphyrin-Fullerene Donor-Acceptor Conjugate. J Phys Chem A 2024. [PMID: 38758579 DOI: 10.1021/acs.jpca.4c00976] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/18/2024]
Abstract
We have designed, synthesized, and characterized a donor-acceptor triad, SPS-PPY-C60, that consists of a π-interacting phenothiazine-linked porphyrin as a donor and sensitizer and fullerene as an acceptor to seek charge separation upon photoexcitation. The optical absorption spectrum revealed red-shifted Soret and Q-bands of porphyrin due to charge transfer-type interactions involving the two ethynyl bridges carrying electron-rich and electron-poor substituents. The redox properties suggested that the phenothiazine-porphyrin part of the molecule is easier to oxidize and the fullerene part is easier to reduce. DFT calculations supported the redox properties wherein the electron density of the highest molecular orbital (HOMO) was distributed over the donor phenothiazine-porphyrin entity while the lowest unoccupied molecular orbital (LUMO) was distributed over the fullerene acceptor. TD-DFT studies suggested the involvement of both the S2 and S1 states in the charge transfer process. The steady-state emission spectrum, when excited either at porphyrin Soret or visible band absorption maxima, revealed quenched emission both in nonpolar and polar solvents, suggesting the occurrence of excited state events. Finally, femtosecond transient absorption spectral studies were performed to witness the charge separation by utilizing solvents of different polarities. The transient data was further analyzed by GloTarAn by fitting the data with appropriate models to describe photochemical events. From this, the average lifetime of the charge-separated state calculated was found to be 169 ps in benzonitrile, 319 ps in dichlorobenzene, 1.7 ns in toluene for Soret band excitation, and ∼320 ps for Q-band excitation in benzonitrile.
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Affiliation(s)
- B Yadagiri
- Department of Polymers and Functional Materials, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500007, India
- Academy of Scientific and Innovative Research, CSIR-IICT, Tarnaka, Hyderabad 500007, India
| | - Ram Ratan Kaswan
- Department of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-5017, United States
| | - Jairam Tagare
- Department of Polymers and Functional Materials, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500007, India
| | - Vinay Kumar
- Department of Polymers and Functional Materials, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500007, India
- Academy of Scientific and Innovative Research, CSIR-IICT, Tarnaka, Hyderabad 500007, India
| | - Manne Naga Rajesh
- Department of Polymers and Functional Materials, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500007, India
- Academy of Scientific and Innovative Research, CSIR-IICT, Tarnaka, Hyderabad 500007, India
| | - Surya Prakash Singh
- Department of Polymers and Functional Materials, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500007, India
- Academy of Scientific and Innovative Research, CSIR-IICT, Tarnaka, Hyderabad 500007, India
| | - Paul A Karr
- Department of Physical Sciences and Mathematics, Wayne State College, 111 Main Street, Wayne, Nebraska 68787, United States
| | - Francis D'Souza
- Department of Chemistry, University of North Texas, 1155 Union Circle, #305070, Denton, Texas 76203-5017, United States
| | - Lingamallu Giribabu
- Department of Polymers and Functional Materials, CSIR-Indian Institute of Chemical Technology, Uppal Road, Tarnaka, Hyderabad 500007, India
- Academy of Scientific and Innovative Research, CSIR-IICT, Tarnaka, Hyderabad 500007, India
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Yahagh A, Kaswan RR, Kazemi S, Karr PA, D'Souza F. Symmetry breaking charge transfer leading to charge separation in a far-red absorbing bisstyryl-BODIPY dimer. Chem Sci 2024; 15:906-913. [PMID: 38239676 PMCID: PMC10793208 DOI: 10.1039/d3sc05034c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2023] [Accepted: 12/14/2023] [Indexed: 01/22/2024] Open
Abstract
Symmetry breaking charge transfer is one of the important photo-events occurring in photosynthetic reaction centers that is responsible for initiating electron transfer leading to a long-lived charge-separated state and has been successfully employed in light-to-electricity converting optoelectronic devices. In the present study, we report a newly synthesized, far-red absorbing and emitting BODIPY-dimer to undergo symmetry-breaking charge transfer leading to charge-separated states of appreciable lifetimes in polar solvents. Compared to its monomer analog, both steady-state and time-resolved fluorescence originating from the S1 state of the dimer revealed quenching which increased with an increase in solvent polarity. The electrostatic potential map from DFT and the time-dependent DFT calculations suggested the existence of a quadrupolar type charge transfer state in polar solvents, and the singlet excited state to be involved in the charge separation process. The electrochemically determined redox gap being smaller than the energy of the S1 state supported the thermodynamic feasibility of the envisioned symmetry-breaking charge transfer and separation. The spectrum of the charge-separated state arrived from spectroelectrochemical studies, revealing diagnostic peaks helpful for transient spectral interpretation. Finally, ultrafast transient pump-probe spectroscopy provided conclusive evidence of diabatic charge separation in polar solvents by far-red pulsed laser light irradiation. The measured lifetime of the final charge-separated states was found to be 165 ps in dichlorobenzene, 140 ps in benzonitrile, and 43 ps in dimethyl sulfoxide, revealing their significance in light energy harvesting, especially from the less-explored far-red region.
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Affiliation(s)
- Aida Yahagh
- Department of Chemistry, University of North Texas 1155 Union Circle #305070 Denton TX 76203-5017 USA
| | - Ram R Kaswan
- Department of Chemistry, University of North Texas 1155 Union Circle #305070 Denton TX 76203-5017 USA
| | - Shahrzad Kazemi
- Department of Chemistry, University of North Texas 1155 Union Circle #305070 Denton TX 76203-5017 USA
| | - Paul A Karr
- Department of Physical Sciences and Mathematics, Wayne State College 111 Main Street Wayne NE 68787 USA
| | - Francis D'Souza
- Department of Chemistry, University of North Texas 1155 Union Circle #305070 Denton TX 76203-5017 USA
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