Strong absorber vs. strong emitter in extended π-conjugated systems: a carbo-benzene – benzothiadiazole chromophore. (16th March 2022)

• Record Type: Journal Article
• Authors: Loaeza, Luis; Maraval, Valérie; Saquet, Alix; Ramos-Ortiz, Gabriel; Chauvin, Remi; Farfán, Norberto
• Is Part Of: New journal of chemistry. Volume 46:Number 14(2022)
• Page Start: 6494
• Page End: 6501
• Publication Date: 2022-03-16
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/d2nj00569g
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : In the search for photoluminescent carbo-benzenes, with the view to measuring the two-photon absorption cross-section by the TPEF method, thienylbenzothiadiazole groups are envisaged as intrinsic fluorophoric substituents through acetylenic linkers. Abstract : In the search for carbo -benzene derivatives with sizable photoluminescent properties, e.g. with the view to measuring the two-photon absorption cross-section with the efficient TPEF method ( vs. the z -scan method), a thienyl-benzothiadiazole (BTD) motif was envisaged as an intrinsic fluorophoric substituent through an acetylenic linker. A quadrupolar tetraphenyl- carbo -benzene with 2 BTD-containing substituents was synthesized from a key [6]pericyclynedione dielectrophile and 2 equiv. of a dihexylthienylbenzothiadiazolylacetylene nucleophile. Reductive aromatization of the resulting [6]pericyclynediol was found to occur in 20% yield using SnCl2 only, a quite high yield in the absence of HCl. The parent benzenic derivative was obtained by Sonogashira coupling of 1, 4-diodobenzene with 2 equiv. of the same terminal alkyne, providing a new fluorophoric oligophenyleneethynylene derivative ([3]OPE) emitting at λ em = 550 nm with a quantum yield of Φ F = 70%. For the highly carbon-rich carbo -benzene-BTD conjugate, the solubility provided by the four hexyl substituents allowed full characterization by 1 H– 13 C NMR spectroscopy and voltammetry, in particular giving a very small absolute potential for a reversible reduction at E 1/2 = −0.53 V/SCE. A classical UV-vis absorption spectrum was recorded, with a maximum band at λ abs1 = 499 nm ( ε 1 = 5.79 10 4 L mol −1 cm −1 ). UV-Vis emission spectra were also recorded, showing residual intrinsic fluorescence of the functional substituents at λ em = 570 nm, at a local minimum of the absorption spectrum before a secondary band at λ abs2 = 612 nm ( ε 2 = 1.75 10 4 L mol −1 cm −1 ). Nevertheless, accurate measurements allowed the determination of the carbo -benzene's fluorescence quantum yield: Φ F = 0.3%. A short analysis of electron delocalization is provided from basic DFT calculations.