The Fluorescent Properties of pH‐Independent Cypridina Oxyluciferin Derivatives.

The co‐factors independent cypridina bioluminescence was often used to detect molecular oxygen. Whereas the native cypridina oxyluciferin and the majority analogues only emit blue light, it limits the application of the cypridina oxyluciferin derivative in detection active oxygen species. To overcome these limitations, we design two series of oxyluciferin derivatives: 2‐acetamido‐5‐aryl‐3‐(p‐trifluoromethylphenyl)pyrazine and 2‐acetamido‐5‐aryl‐3‐(p‐methoxylphenyl)pyrazine. The results found that the fluorescence emissions of the cypridina oxyluciferin derivatives cover the whole region of visible light. Especially, 2‐acetamido‐5‐(trans‐2,3,6,7‐tetrahydro‐1H,5H‐benzo[i,j]quinolizine‐ethenyl)‐3‐(p‐trifluoromethyl phenyl)pyrazine (1 h) can emit red light. By comparison of the emission spectra and oscillator strengths, it found that electron‐donating group in C3 position contributed to blue shift wavelength and improve luminous efficiency. The increasing conjugated length by introducing a conjugated double bond made the emission spectra shift to red and the luminescence strengths much stronger. Moreover, the analysis of the relative stabilities at the ground and excited states indicates that neutral forms, not amide ions, are dominant at physiological pH. [ABSTRACT FROM AUTHOR]