Methyl-group effect on the photoluminescence property of a spiro[fluorene-9,9'-xanthene] derivative: a structural and spectroscopic study

In this work, we explore the structural and photoluminescent properties of 1',3',6',8'-tetramethylspiro[fluorene-9,9'-xanthene] (TMSFX), C₂₉H₂₄O. TMSFX was synthesized via a one-pot method and crystallized in the monoclinic space group P2₁/c. Single-crystal X-ray diffraction revealed a unique 90° crossover between the fluorene and xanthene segments. Photoluminescence studies showed that TMSFX exhibits strong blue-white fluorescence on excitation at 321 nm, with emission peaks at 405 and 431 nm, and a fluorescence lifetime of 3.1 ns. In contrast, the methyl-free analog spiro[fluorene-9,9'-xanthene] (SFX) is non-luminescent, highlighting the critical role of methyl groups in enhancing fluorescence. These findings demonstrate the significance of methyl groups in tuning the photophysical properties of organic molecules for potential optoelectronic applications.