Issue 33, 2017

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

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 (CF3λmax = 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

Supplementary files

Article information

Article type
Paper
Submitted
30 May 2017
Accepted
16 Jun 2017
First published
16 Jun 2017

Org. Biomol. Chem., 2017,15, 6913-6920

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, 15, 6913 DOI: 10.1039/C7OB01319A

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