Influence of substituent position on thermal properties, photoluminescence and morphology of pyrene–fluorene derivatives

• New position-dependent conjugated hydrocarbon fluorenyl–pyrenes were synthesized by Suzuki cross-coupling reaction.
• All compounds exhibited deep blue fluorescence with excellent quantum yields (≈78% in dichloromethane).
• The substituent number and positions affected thermal properties, solubility, optical properties and the morphology.

New position-dependent conjugated hydrocarbon dyes containing a pyrene core and multi-fluorene moieties 3 have been synthesized and characterized by 1H/13C NMR spectroscopy, as well as by optical and theoretical studies. The solubility of mono-, bis- and tetra-fluorenyl–pyrene 3 tends to decrease and leads to varied thermal properties. The results of the optical studies and DFT calculations revealed that the energy gap can be easily modified or fine-tuned by either varying the substituent number or position. Remarkably, such pyrene–fluorene materials exhibited deep blue fluorescence (λmax = 400–458 nm in CH2Cl2) with excellent quantum yields (≈78%). These results suggest that these new pyrene–fluorene derivatives have potential application in OLED technology as blue host materials.

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