Push鈥揚ull Porphyrin-Containing Polymers: Materials Exhibiting Ultrafast Near-IR Photophysics

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• 作者：Xiaorong Wang ; Gessie Brisard ; Daniel Fortin ; Paul-Ludovic Karsenti ; Pierre D. Harvey
• 刊名：Macromolecules
• 出版年：2015
• 出版时间：October 13, 2015
• 年：2015
• 卷：48
• 期：19
• 页码：7024-7038
• 全文大小：1007K
• ISSN：1520-5835

文摘

Four push鈥損ull polymers of structure (C鈮鈥?b>[Zn]鈥揅鈮鈥?b>A)_n (A = isoindigo (P1), bis(伪-methylamino-1,4-benzene)quinone (P2), 2-(N-methylamino-1,4-benzene)-N-1,4-benzene-maleimide (P3), and 2,2鈥?anthraquinone (P4); [Zn] = [bis(meso-aryl)porphyrin]zinc(II) = donor) and models M1 and M2 (A鈥测€揅鈮鈥?b>[Zn]鈥揅鈮鈥?b>A鈥? A鈥?= respectively naphtoquinone and 2-anthraquinone) were prepared and characterized (¹H and ¹³C NMR, elemental analysis, GPC, TGA, cyclic voltammetry, steady state and ultrafast time-resolved UV鈥搗is and emission spectroscopy) and studied by density functional theory (DFT) and time-dependent DFT (TDDFT) in order to address the nature of the low-lying singlet and triplet excited states. P1 (fully conjugated polymer), P2 (formally nonconjugated but exhibit strong electronic communication accross the chain) and P4 (formally nonconjugated but local conjugation between the donor and acceptor) are near-IR emitters (位_max > 750 nm). M1 and M2 are mono-C鈮鈥?b>[Zn]鈥揅鈮 species, and P3 exhibits a very modest CT contribution (as maleimide is a weak acceptor) and are not near-IR emitters. The nature of the S₁ and T₁ excited states are CT processes donor* 鈫?acceptor. In P1鈥?b>P4, a dual fluorescence (7.7 < 蟿_F < 770 ps; except one value at 2.5 ns; P3) is depicted, which are assigned to fluorescences arising from the terminal and central units of the polymers identified from the comparison with M1 and M2. The high and low energy fluorescences are respectively short (77 < 蟿_F < 166 ps) and long-lived (688 < 蟿_F < 765 ps) suggesting S₁ energy transfers with rates, k_ET, of 7.1 (P1), 12 (P2) and 4.5 (ns)^鈭? (P4). The fs transient absorption spectra exhibit particularly very short triplet lifetimes (2.3 < 蟿_T1 < 87 ns) explaining the absence of phosphorescence. Also ultrafast lifetimes (85 < 蟿 < 1290 fs) for species excited in the 0鈥? peak of the Q-band (650 nm; i.e., 蟺蟺* porphyrin level) indicating its rather efficient nonradiative deactivation (S_n 鈭?> S₁ and S_n 鈭?> T_m). When cooling takes place or the solution concentration is increased, new red-shifted fluorescence bands appear, evidencing aggregate formation. Both fluorescence and transient absorption lifetimes of P1鈥?b>P4 become shorter and their band intensity lower. Finally, the position of the optically silent phosphorescence has been predicted to be in the 1300 (P1, P2) and 1000 nm (P3, P4) zones (DFT).