**6.2 Stable dioxetene chemiluminescence probe**

Dioxetene chemistry offers potential for selective and sensitive detection of <sup>1</sup> O2. McNeill and co-workers reported "trap and trigger" Chemiluminescence probe for 1 O2 [46] using Schaap's dioxetene [47] enol ether precursor to trap the 1 O2 in the first step and in the second step Chemiluminescence was triggered by adding fluoride ion. This probe was limited application in organic solvents due to the quenching mechanism of the emitting species in water [48]. Nir Hananya et al. developed a new Chemiluminescence probe by incorporating an electron withdrawing substituent at the ortho position of phenol group of Schaap's dioxetene, namely SOCL-CPP [15] (**Figure 15**). SOCL-CPP reacts with <sup>1</sup> O2 to generate a phenol-dioxetene species that spontaneously decompose in aqueous medium to generate corresponding electronically excited benzoate ester [15].

A green light emission is obtained from excited benzoate ester. The incorporation of acrylic acid substituent at the ortho position of phenol is to generate a donor-acceptor

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

#### **Figure 15.**

*Structure of SO chemiluminescent probe* **SOCL** *and its chemiexcitation pathway upon reaction with 1 O2 (adapted from [15]).*

pair that enhances the emissive nature of benzoate intermediate [15]. Addition of a chlorine substituents at the ortho position reduces the pKa of the phenol and thus enriches the percentage of phenoxy ion that eventually accelerate the chemiexcitation kinetics of the phenol-dioxitene species to monitor in real time.

### **7. Conclusions**

Singlet oxygen as a highly reactive form of molecular oxygen plays a vital role in many environmental and biomedical processes. Selective and sensitive detection and quantification of singlet oxygen species provides crucial information for understanding its involvement and mechanism in various processes. EPR method for the detection of 1 O2 has major disadvantage of requiring an expensive instrument and complicated operating procedures. Direct photoluminescence measurement from <sup>1</sup> O2 at about 1270 nm is useful for singlet oxygen detection but that also suffers drawback due to very low quantum efficiency. UV–Vis absorbance probes for selective detection of <sup>1</sup> O2 is significant but low sensitivity put some limitation for spectrophotometric method. Molecular fluorescence or lanthanide based fluorescence probe and Chemiluminescence probe provides high sensitivity and desirable selectivity, therefore ensure great potential for singlet oxygen detection. Additional benefits of fluorescence probe including the capability of detection of <sup>1</sup> O2 among various other reactive oxygen species. The temporal and spatial resolution of these probes can provide detailed information on site and the kinetics of singlet oxygen production or decay. In comparison to organic fluorescence probe, lanthanide complex based time gated luminescence probe possess many advantages such as long luminescence lifetime, large Stokes shift and sharp emission profile that makes them suitable for time gated detection mode for minimising background luminescence interference. Chemiluminescence probes does not require any excitation light sources, can be applied in certain cases where background fluorescence and various light scattering phenomena lower the signal to noise ratio. Furthermore, due to high sensitivity

of Chemiluminescence detection, only low concentration of probe is necessary eventually decreasing the occurrence of artifactual interference of secondary reactions. Although, much has been conferred in this concise chapter, perhaps these are not all, but the future will invoke more questions and thus newer and emerging methods, would help expand the level of our understanding.
