Detection method

An optical sensing element for vapour phase detection of hydrogen peroxide, the optical sensing element comprising a sensing compound provided as a coating on a substrate, wherein the sensing compound is a compound that on exposure to hydrogen peroxide forms a luminescent reporter compound when excited with stimulating radiation at a predetermined wavelength that the sensing compound does not absorb, and wherein the sensing compound is a compound of general formula:

• in which:
• each R group can be the same or different C2-5 alkyl moiety or together with the oxygen atoms to which they are attached form a cyclic structure containing up to 5 carbon atoms, optionally substituted by one or more C1-4 alkyl groups;
• Ar1 is a (hetero)aromatic moiety and/or comprises fused (hetero)aromatic rings or a chain of (hetero)aromatic or fused (hetero)aromatic rings moieties;
• Ar2 is an aromatic unit with electron withdrawing groups attached or a higher electron affinity heteroaromatic moiety selected from an imidazole, pyrazine, triazole, benzotriazole, thiadiazolebenzotriazole, oxadiazole, oxazole, thiazole, thiadiazole, benzothiadiazole, benzobis(thiadiazole), quinoxaline, and thiodiazoloquinoxaline;
• R′ is a solubilising group selected from straight or branched chain alkyl groups containing up to 10 carbon atoms, ethylene glycol chains including 2-methoxymethyl, 2-methoxyethyl, 2-(2-methoxyethoxy)ethyl, and 2-(2-(2-methoxyethoxy)ethoxy)ethyl, and dendrons that include one or more aryl rings and/or hetero atoms;
• m is an integer equal to 1 or greater;
• n is an integer equal to 1 or greater;
• L is a linker unit that is present when n is greater than 1, wherein L is a polymer, carbon atom or alkyl group;
• and/or
• wherein the sensing compound is selected from the following compounds