**6.1 TTF substituted singlet oxygen probe: 2-methyl-6-phenyl-3,7 dihydroimidazo[1,2-α]pyrazine-3-one (CLA), MCLA and FCLA**

A number of Chemiluminescence probes have been developed in recent years for 1 O2 detection. Among the mostly used Chemiluminescence probes for <sup>1</sup> O2 includes 2-methyl-6-phenyl-3,7-dihydroimidazo[1,2-α] pyrazine-3-one (CLA), and its derivatives MCLA and FCLA [41–43] (shown in **Figure 13**). These compounds are very good in detecting <sup>1</sup> O2 and spontaneously emit light but the major drawback of these compound is that they not only reacts with singlet oxygen but also with superoxide anion; thus lacks the selectivity for <sup>1</sup> O2.

Chemiluminescence probe with a strong electron donor tetra thiafulvalenem (TTF) and anthracene as a luminophore possess excellent selectivity and sensitivity for <sup>1</sup> O2 detection. As TTF moiety is a strong electron donor, it enhances the reaction between anthracene skeleton to react specifically with <sup>1</sup> O2 to form highly luminescent endoperoxide.

Guanxin Zhang et al. reported 4,4′(5′)-bis[2-(9-anthryloxy)ethylthio] tetrathiafulvalene (as shown in **Figure 14**) as selective and sensitive probe for <sup>1</sup> O2 with a much better response for <sup>1</sup> O2, representing better selectivity than CLA [40, 44]. 4,5-dimethylthio-4′-[2-(9-anthryloxy) ethylthio] tetrathiafulvalene was another Chemiluminescence probe with similar functionality [40, 45]. A linear relationships between the Chemiluminescence intensity and the amount of <sup>1</sup> O2 was found for H2O2/ClO− system and the LOD of 76 nM/L was reported for 1 O2. In mixed solvent of

#### **Figure 13.**

*(a) The chemical structure of CLA and its reaction with singlet oxygen; (b) the chemical structure of MCLA and (c) the chemical structure of FCLA (adapted from [41–43]).*

#### **Figure 14.**

*The chemical structure and reaction scheme of (a) 4,4*′*(5*′*)-bis[2-(9-anthryloxy)ethylthio] tetrathiafulvalene, (b) 4,5-dimethylthio-4*′*-[2-(9-anthryloxy)ethylthio] tetrathiafulvalene with with 1 O2 and (c) the chemical structure of tetrathiafulvalene-anthracence dyad1 (adapted from [40, 44, 45]).*

tetrahydrofuran and H2O, both the probes cannot be applied. However, tetrathiafulvalene-anthracence dyad1 (as shown in **Figure 13c**) dissolve easily in methanol and ethanol and permits detection of 1 O2 under relatively low polarity solvent.
