New experimental method for determining the S₁ → Sn absorption spectrum of highly fluorescent dyes

A new method has been developed to measure the excited-state absorption cross sections σ 1n , of highly fluorescent dyes. which gives excited singlet-state absorption (ESSA) spectra over most of the UV–visible region, including the one where the fluorescence occurs. The error in the σ 1n values depends on that for the singlet excited-state concentration. Our method used benzophenone as an actinometer to determine the excited-state concentration. Rhodamine 6G was used to test the method; the ESSA spectrum obtained shows a maximum around 530 nm with an excited-state absorption cross section σ 1n value of 2.08 × 10 −16 cm 2 . Our results are discussed and compared with those reported in the literature.