Spectroscopic studies on the lanthanide sensitized luminescence and chemiluminescence properties of fluoroquinolone with different structure

Lanthanide sensitized luminescence and chemiluminescence (CL) are of great importance because of the unique spectral properties, such as long lifetime, large Stokes shifts, and narrow emission bands characteristic to lanthanide ions (Ln3+). With the fluoroquinolone (FQ) compounds including enoxacin (ENX), norfloxacin (NFLX), lomefloxacin (LMFX), fleroxacin (FLRX), ofloxacin (OFLX), rufloxacin (RFX), gatifloxacin (GFLX) and sparfloxacin (SPFX), the luminescence and CL properties of Tb3+–FQ and Eu3+–FQ complexes have been investigated in this contribution. Ce4+–SO32− in acidic conditions was taken as the CL system and sensitized CL intensities of Tb3+–FQ and Eu3+–FQ complexes were determined by flow-injection analysis. The luminescence and CL spectra of Tb3+–FQ complexes show characteristic peaks of Tb3+ at 490 nm, 545 nm, 585 nm and 620 nm. Complexes of Tb3+–ENX, Tb3+–NFLX, Tb3+–LMFX and Tb3+–FLRX display relatively strong emission intensity compared with Tb3+–OFLX, Tb3+–RFX, Tb3+–GFLX and Tb3+–SPFX. Quite weak peaks with unique characters of Eu3+ at 590 nm and 617 nm appear in the luminescence and CL spectra of Eu3+–ENX, but no notable sensitized luminescence and CL of Eu3+ could be observed when Eu3+ is added into other FQ. The distinct differences on emission intensity of Tb3+–FQ and Eu3+–FQ might originate from the different energy gap between the triplet levels of FQ and the excited levels of the Ln3+. The different sensitized luminescence and CL signals among Tb3+–FQ complexes could be attributed to different optical properties and substituents of these FQ compounds. The detailed mechanism involved in the luminescence and CL properties of Tb3+–FQ and Eu3+–FQ complexes has been investigated by analyzing the luminescence and CL spectra, quantum yields, and theoretical calculation results.

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► Provide new insight into the luminescent properties of Ln3+–FQ complexes.
► Spectroscopic properties of Ln3+–FQ vary greatly with different FQ and Ln3+.
► Mechanism was discussed based on spectral analysis and theoretical calculations.