**3.3 9-[2-(3-Carboxy-9,10-dimethyl)anthryl]-6-hydroxy-3H-xanthen-3-one (DMAX)**

Following the same approach of Umezawa group, Tanaka et al. synthesised another fluorescence probe molecule for the faster and efficient detection of 1 O2, 9-[2-(3-carboxy-9,10-dimethyl)anthryl]-6-hydroxy-3H-xanthen-3-one (DMAX) (**Figure 8**), targeting to achieve great sensitivity and rapid rate of formation of endoperoxide compare to already reported one i.e. DPAX (**Figure 8**) [27]. The crucial point of DMA compound is that it reacts rapidly with <sup>1</sup> O2 to give the 9,10 endoperoxide, DMA-EP with rate constant k = 9.1 × 108 M−1 s−1 in water. This observation clearly indicates that DMAX shows much greater sensitivity for <sup>1</sup> O2 than DPAX. Comparing to this reaction, the classical singlet oxygen trap 1,3-diphenylisobenzophuran (DPBF) reacts with <sup>1</sup> O2 with a comparable rate constant k = 9.6 × 108 M−1 s−1 but DPBF reacts with other reactive oxygen species like hypochlorite, hydroxyl radical to generate the same products.

Both DMAX and its endoperoxide DMAX-EP have similar excitation and emission wavelength (λex = 492 nm and λem = 515 nm) but DMAX-EP is highly fluorescent whereas DMAX itself is practically non-fluorescent (**Figure 8**). From their study Tanaka et al. confirmed that fluorescence intensity of DMAX increases with

#### **Figure 8.**

*Reaction of 9-[2-(3-carboxy-9,10-dimethyl)anthryl]-6-hydroxy-3H-xanthen-3-one (DMAX) with 1 O2 to produce DMAX-EP (adapted from [27]).* λ*ex = 492 nm and* λ*em = 515 nm.*

#### **Figure 9.**

*Initial rate of fluorescence increase of DMAX (in hollow sphere) and DPAX-1(in hollow square) with increasing concentration of EP-1 [adapted from [27]].*

*Photophysical Detection of Singlet Oxygen DOI: http://dx.doi.org/10.5772/intechopen.99902*

concentration dependent manner of singlet oxygen generator, 3-(1,4-Dihydro-1,4 epidioxy-4-methyl-1-naphthyl)propionic acid (EP-1) and a good linear relationship has been observed for fluorescence intensity and concentration of EP-1. This enables DMAX to use as a quantitative detection probe for <sup>1</sup> O2. **Figure 9** demonstrate the change of gradient of fluorescence intensity of DMAX and DPAX-1 with increasing concentration of EP-1 having gradient 1.0 and 1.9 × 10−2 (arbitrary unit)s−1[EP-1 (mM)]−1 for DMAX and DPAX respectively. This result suggests that DMAX reacts with 1 O2 more rapidly and sensitivity is 53 times more than that of DPAX [27].

Tanaka et al. further confirmed that DMAX did not show any change in fluorescence intensity upon reaction with 1.0 mM H2O2, 0.1 mM nitric oxide and 0.2 mM superoxide suggesting the specificity towards <sup>1</sup> O2. Further the hydrophobicity of DMAX is less than that of DPAXs making it suitable to use for assays in biological sample [27].
