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Unusual solvent polarity dependent excitation relaxation dynamics of a bis[: P -ethynyldithiobenzoato]Pd-linked bis[(porphinato)zinc] complex

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Title
Unusual solvent polarity dependent excitation relaxation dynamics of a bis[: P -ethynyldithiobenzoato]Pd-linked bis[(porphinato)zinc] complex
Author(s)
Jaehong Park; Tae-Hong Park; Louise E. Sinks; Pravas Deria; Jiyong Park; Mu-Hyun Baik; Michael J. Therien
Publication Date
2018-02
Journal
MOLECULAR SYSTEMS DESIGN AND ENGINEERING, v.3, no.1, pp.275 - 284
Publisher
ROYAL SOC CHEMISTRY
Abstract
We report the synthesis and excited-state dynamics of a bis[p-ethynyldithiobenzoato]Pd(ii)-bridged bis[(porphinato) zinc(ii)] complex (PZn-Pd(edtb)2-PZn) that exhibits unusual solvent dielectric (ϵ)-dependent excited-state relaxation behavior. In nonpolar toluene solvent, PZn-Pd(edtb)2-PZn manifests an ultrafast S1 → T1 intersystem crossing time constant (τISC ≈ 2 ps), a broad, high-oscillator strength T1 → Tn transient absorption manifold (λmax(T1 → Tn) = 940 nm), and a near unity triplet-state formation quantum yield (ΦT ≈ 1; τT = 2.2 μs). In contrast, in moderately polar solvents (e.g., dichloromethane (DCM) or THF), the S1 → T1 intersystem crossing quantum yield is significantly suppressed (ΦT ≈ 0.2; τF ≈ 60 ps in DCM). Comparative femtosecond transient absorption studies in DCM and mixed DCM/toluene solvent systems reveal a new low-energy stimulated emission signal, the λmaxem of which is highly sensitive to solvent polarity. The lack of spectral signatures for radical species, and the emergence of intense stimulated emission indicate an additional low energy electronically excited-state (S∗), populated via S1-state relaxation, that also possesses substantial singlet character. As solvent polarity is progressively increased, the energy of S∗ progressively decreases, eventually becoming lower than the S1 state and providing an excited-state relaxation channel that bypasses T1 state formation. These data show that the nature of the PZn-Pd(edtb)2-PZn excited-state dynamics is strongly influenced by the solvent dielectric, and that this Pd(ii)-based linker motif offers new opportunities to engineer excited-state spin distributions and lifetimes in strongly conjugated chromophore assemblies. © 2018 The Royal Society of Chemistry
URI
https://pr.ibs.re.kr/handle/8788114/4733
ISSN
2058-9689
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Center for Catalytic Hydrocarbon Functionalizations(분자활성 촉매반응 연구단) > Journal Papers (저널논문)
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