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Synthesis of selectively 4-substituted 9,9′-spirobifluorenes and modulation of their photophysical properties

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Abstract

Synthesis of selectively 4-substituted 9,9′-spirobifluorenes was accomplished by using catalytic [2 + 2 + 2]-cyclotrimerization of specifically substituted diynols with alkynes to the corresponding fluorenols. Further synthetic transformations provided the target molecules. The measurement of the photophysical properties of the prepared 4-substituted 9,9′-spirobifluorenes revealed that their emission maxima depended on the electronic properties of the substituents present in the para position: the presence of an electron accepting group strongly favored the maxima red shift toward the blue VIS region (CF3 λmax = 361 nm vs. MeO λmax = 330 nm). Adding further substituents (aryl or arylethynyl moieties) on the phenyl ring in position 4 did not lead to a dramatic improvement in the emission maxima (CF3C6H4, λmax = 369 nm, CF3C6H4C[triple bond, length as m-dash]C, λmax = 370 nm), but increased their quantum yields considerably. In addition, a series of 9,9′-spirobifluorenes possessing various extended π-systems (pyrene, anthracene, etc.) were synthesized. In general, the emission maxima pattern reflected that of the parent π-systems, but they were red shifted by 10–30 nm. Finally, also a 1-[4-(9,9′-spirobifluorene-4-yl)phenyl]-2-aryl-ortho-carborane was prepared. These data thus may provide guidelines for further design of 9,9′-spirobifluorenes with tailored properties.

Graphical abstract: Synthesis of selectively 4-substituted 9,9′-spirobifluorenes and modulation of their photophysical properties

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Publication details

The article was received on 30 May 2017, accepted on 16 Jun 2017 and first published on 16 Jun 2017


Article type: Paper
DOI: 10.1039/C7OB01319A
Citation: Org. Biomol. Chem., 2017, Advance Article
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    Synthesis of selectively 4-substituted 9,9′-spirobifluorenes and modulation of their photophysical properties

    R. P. Kaiser, J. Mosinger, I. Císařová and M. Kotora, Org. Biomol. Chem., 2017, Advance Article , DOI: 10.1039/C7OB01319A

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