Photophysics of Oligothiophenes End‐Capped with Platinum(II) Auxochromes. Issue 2 (1st October 2020)

• Record Type: Journal Article
• Authors: Gundogan, Ali S.; Jagadesan, Pradeepkumar; Schanze, Kirk S.
• Is Part Of: ChemPhotoChem. Volume 5:Issue 2(2021)
• Page Start: 160
• Page End: 166
• Publication Date: 2020-10-01
• Subjects: intersystem crossing -- oligothiophenes -- platinum -- spin-orbit coupling -- triplet states; Photochemistry -- Periodicals; Periodicals; Electronic journals; 541.35
• DOI: 10.1002/cptc.202000123
• Languages: English
• ISSNs: 2367-0932

Abstract

Abstract: A series of four oligothiophenes end‐capped with −Pt(PBu3 )2 Cl moieties on both ends of the oligomers was synthesized, and their excited state properties were investigated. The observation of low fluorescence quantum yield (<2 %) for the oligomers indicates the strong effect of platinum on the intersystem crossing (ISC) efficiency. No phosphorescence was detected for any of the oligomers; however, strong triplet‐triplet absorption was observed by nanosecond transient spectroscopy for oligomers with more than one thiophene unit. The oligomers displayed short triplet lifetimes (∼1–2 μs) compared to the unmetallated oligomers, due to large spin‐orbit coupling induced by the platinum atom. The lower limits of the ISC yields were indirectly determined by measuring the singlet oxygen quantum yields. Femtosecond–picosecond transient absorption studies revealed that the ISC rate ranges from 10 12 –10 10 s −1, decreasing with increasing oligomer length. Electrochemical studies showed that the oligomers exhibit relatively low oxidation potentials (ca. 0.1 V vs. Fc/Fc + ). Quenching of the oligomers' triplet state absorption, simultaneously with the rise of their corresponding cationic radical absorption band in nanosecond transient spectra in the presence of methyl viologen, as an electron acceptor, established that the electron transfer occurs from their triplet state. Abstract : Metal matters : A series of four thiophene oligomers featuring −Pt(PBu3 )2 Cl units on both the ends of the chains were synthesized and studied. Oligomers with two or more thiophenes exhibit larger spin−orbit coupling induced by the platinum atom compared to the unmetallated thiophene oligomers, and the intersystem crossing (ISC) rate in oligomers slows down as the oligomer chain length increases.