Measurement of rate constants for quenching singlet oxygen with a Cypridina luciferin analog (2‐methyl‐6‐[p‐methoxyphenyl]‐3,7‐dihydroimidazo[1,2‐a]pyrazin‐3‐one) and sodium azide

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Abstract
The rate constants for [1O2] [MCLA] and [1O2][NaN3] were measured by quenching the near-infrared emission (1Δg→3∑g) in steady state with MCLA and NaN3, respectively. 1O2 was constantly generated by energy transfer to O2 from Ar laser-excited Rose Bengal. The Stern—Volmer plots yielded the second-order rate constants of 2.94 × 109 M−1 S−1 and 3.83 × 108 M−1 S−1 for quenching 1O2 with MCLA and NaN3 in water at pH 5.4, respectively. The 1O2 + MCLA reaction emitted light with maximum at 465 nm at pD 4.5 identical to the O2− + MCLA reaction.