Intersystem Crossing in Naphthalenediimide-Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

Year: 2019

Authors: Hussain M., Taddei M., Bussotti L., Foggi P., Zhao JZ., Liu QY., Di Donato M.

Autors Affiliation: Dalian Univ Technol, Sch Chem Engn, State Key Lab Fine Chem, E-208 West Campus,2 LingGong Rd, Dalian 116024, Peoples R China; LENS European Lab Nonlinear Spect, Via N Carrara 1, I-50019 Sesto Fiorentino, Italy; Ist Nazl Ottica Largo Enrico, INO, Fermi 6, I-50125 Florence, Italy; Univ Perugia, Dipartimento Chim, Via Elce Sotto 8, I-06123 Perugia, Italy; Shandong Univ Sci & Technol, Coll Chem & Environm Engn, Qingdao 266590, Shandong, Peoples R China.

Abstract: Oxoverdazyl (Vz) radical units were covalently linked to the naphthalenediimide (NDI) chromophore to study the effect of the radical on the photophysical properties, especially the radical enhanced intersystem crossing (REISC), which is a promising approach to develop heavy-atom-free triplet photosensitizers. Rigid phenyl or ethynylphenyl linkers between the two moieties were used, thus REISC and formation of doublet (D-1, total spin quantum number S=1/2) and quartet states (Q(1), S=3/2) are anticipated. The photophysical properties of the dyads were studied with steady-state and femtosecond/nanosecond transient absorption (TA) spectroscopies and DFT computations. Femtosecond transient absorption spectra show a fast electron transfer (<150 fs), and ISC (ca. 1.4-1.85 ps) is induced by charge recombination (CR, in toluene). Nanosecond transient absorption spectra demonstrated a biexponential decay of the triplet state of the NDI moiety. The fast component (lifetime: 50 ns; population ratio: 80 %) is assigned to the D-1 -> D-0 decay, and the slow decay component (2.0 mu s; 20 %) to the Q(1)-> D-0 ISC. DFT computations indicated ferromagnetic interactions between the radical and chromophore (J=0.07-0.13 eV). Reversible formation of the radical anion of the NDI moiety by photoreduction of the radical-NDI dyads in the presence of sacrificial electron donor triethanolamine (TEOA) is achieved. This work is useful for design of new triplet photosensitizers based on the REISC effect.

Journal/Review: CHEMISTRY-A EUROPEAN JOURNAL

Volume: 25 (68)      Pages from: 15615  to: 15627

More Information: J.Z. thanks the NSFC (21673031, 21761142005, 2181101275, and 21421005), the Fundamental Research Funds for the Central Universities (DUT2019TA06), and State Key Laboratory of Fine Chemicals (ZYTS201901) for financial support.
KeyWords: electron transfer; intersystem crossing; naphthalenediimide; photocatalysis; triplet photosensitizer
DOI: 10.1002/chem.201903814

Citations: 13
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