The Luminescence of Pd and Pt Benzohydroporphyrazines in the Near-IR Range
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The Luminescence of Pd and Pt Benzohydroporphyrazines in the Near-IR Range P. P. Pershukevicha, D. I. Volkovicha, E. A. Makarovab, E. A. Lukyanetsb, and K. N. Solovyova, * a
Stepanov Institute of Physics, National Academy of Sciences of the Republic of Belarus, Minsk, 220072 Belarus b Organic Intermediates and Dyes Institute (NIOPIK), Moscow, 123995 Russia *e-mail: [email protected] Received March 25, 2020; revised March 25, 2020; accepted July 7, 2020
Abstract—The phosphorescence of three new palladium and three platinum complexes of benzo-fused hydroporphyrazines—analogues of phthalocyanine, in which molecule one or two isoindole fragments are replaced by a hydrogenated pyrrole ring which gives macrocycles of the type of chlorin, bacteriochlorin, and isobacteriochlorin—analogues of photosynthetic pigments, is studied in the near-IR range under stationary lamp excitation. The phosphorescence spectra of the complexes of trans-dibenzotetrahydroporphyrazines are recorded for the first time (for both platinum and palladium) which could not be found for a long time because of the unprecedented remoteness of the 0–0 bands from the visible region (1.67, 1.52 μm for Pd, Pt) as well as because of the low quantum yield of phosphorescence. The fluorescence of these complexes in the near-IR range is found as well. The approximate additivity of the action of the structural factors—hydrogenation of the pyrrole rings, aza-substitution, and benzo-substitution—on the energy of the lowest triplet state T1 is shown based on the comparison of the experimental results with the own and published data for palladium complexes of the tetrapyrrole series. The obtained information is substantial for the targeted creation of emitters in the near-IR range (1.0–1.7 μm). Keywords: palladium and platinum complexes of benzohydroporphyrazines, trans-dibenzotetrahydroporphyrazine, analogues of phthalocyanine, near-IR range, absorption spectrum, phosphorescence spectrum, quantum yield of phosphorescence, lowest triplet state, luminescence of singlet oxygen DOI: 10.1134/S0030400X20110181
INTRODUCTION In regard to studying the connection of physical properties with the structure of tetrapyrrole molecules and searching for the ways of their practical applications in the IR range, we synthesized Pd and Pt complexes based on new analogues of phthalocyanine and hydroporphyrazines–benzohydroporphyrazines. Arenohydroporphyrazines [1–4] and their derivatives [5] are a new subclass of tetrapyrrole compounds with intensive absorption in the near-IR range (NIR). The spectral–luminescent properties of benzohydroporphyrazines—zinc complexes [6] and corresponding free bases [6, 7]—were studied by our research group. NIR phosphorescence of the palladium and platinum complexes with tetramethyltribenzodihydroporphyrazine and octamethyldibenzotetrahydroporphyrazine with the adjacent position of the hydrogenated tetrapyrrole rings was recorded in [8]. In this work, we applied (throughout the whole text) the following designations:
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