Quantum theory of atoms-in-molecules and Hirshfeld surface analyses indicated an increase in the extent of (i) C-H···H-C; (ii) C-H···O, (iii) π-π interactions and a decrease in the extent of (i) σ-π interaction, (ii) an interplanar angle between the vicinal pyrene units in a series of acetylpyrene derivatives offering blue-green-orange emissive crystals.
Ultrafast intersystem crossing of carbonylpyrenes in chloroform was investigated by femtosecond pump-probe spectroscopy. When compared to the dominant fluorescence decay pathway in pyrene, carbonyl functionalized pyrenes display near-unity triplet formation upon photoexcitation. The excited singlet state (S) undergoes rapid intersystem crossing (k) concomitantly with internal conversion (k) to lower excited singlet states (S) within a timescale of 5-11 ps (1/τ = k + k). Furthermore, intersystem crossing from lower excited singlet states (S) proceeds through coupling with receiver triplet states, eventually leading to high triplet quantum yields (Φ = 97%; tetraacetylpyrene). Followed by internal conversion in the triplet manifolds, phosphorescence decay on a microsecond timescale is observed from the emitter triplet state.
We report the synthesis, X-ray structures and photophysical properties of a few benzoylpyrene (BP) derivatives. Steric hindrance due to incremental benzoyl groups causes a systematic reduction in the orbital overlap (π-π) between vicinal pyrene units affording green-yellow-orange solid-state emitters. Crystallization induced emission could arise from: i) electronic (dipolar/excitonic) interactions, ii) arrested bond rotations, and/or iii) lack of solvation in crystalline 1-4BP (Φ Fl ∼ 2-26%) when compared to that in solution (Φ Fl ≤ 1%). Our earlier effort [Chem. Commun. 2014, 50, 8644] on progressive acylation, in contrast to benzoylation, results in a gradual increase in the π-π overlap between vicinal pyrenes.
A series of extended π-conjugated benzophenone analogs was synthesized through a facile Lewis-acid catalyzed Friedel–Crafts reaction in order to exploit the integral triplet state properties of benzophenone.
C–H⋯H–C and C–H⋯π interaction assisted formation of thermodynamically stable blue emissive AP-I from kinetically stable green emissive AP-II of 1-(anthracen-9-yl)pyrene (AP).
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