Abstract
The steady state and subnanosecond time-resolved fluorescence properties of oxyluciferin and its structural analogues luciferin (LH 2), 6′-methoxyluciferin (MeOLH 2) and 2-cyano-6-hydroxybenzothiazole (BT) were investigated in aqueous (pH 1–10) and ethanol solutions. The structures of the three fluorescence emitters were identified as follows: blue, enol-phenolate; yellow—green, phenol; red, phenolate of keto form. The dissociation rate of the excited luciferin 6′-hydroxyl group is shown to be lower than the rate of emission by the phenol form itself and, consequently, although ground and excited p K values differ considerably (8.5 and −0.5 respectively), blue fluorescence is observed in non-polar and strong acidic aqueous solutions. Fluorescence decay curves for oxyluciferin and its analogues (blue and yellow—green emission maxima) were obtained in water (pH 7.8) and ethanol (96%).
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