Triplet-Triplet fluorescence of 9,10-dibromanthracene in hexane

The temperature dependence of the triplet-triplet fluorescence (TTF) spectrum of 9,10-dibromanthracene in hexane is studied in the near infrared region between 800 and 1050 nm in the temperature range from 200 to 320 K. The TTF spectrum exhibits two distinct bands at 842 and 949 nm at 293 K. Upon cooling from 293 to 200 K, the intensity of the 842-nm band decreases and that of the 949-nm band increases. The different behavior of the band intensities is explained by the overlap of the emission at 950 nm, which can be related to a photoproduct. The 842-nm band is assigned to the 0-0 T ₂(³ B _1g →T ₁(³ B _2u transition. The quantum yield of TTF at 293 K measured within the 842-nm band is 8.3×10^?7 (±20%)), and for emission in the region from 800 to 1050 nm it is equal to 1.4×10^?6 (after subtraction of the contribution from the S ₁→S ₀ singlet-singlet fluorescence). The effect of the intersystem crossing and internal conversion on the temperature dependence of TTF is discussed.