To clarify the acyl substitution effect on the fluorescent property of Cypridina oxyluciferin analogs, which have the 4-(dimethylamino)phenyl group at C5, we compared the spectroscopic properties of benzamide 1b and its 2,6-dimethylphenyl derivative 1c in various solvents with those of acetamide 1a. Similarity of the fluorescence wavelengths of 1a–c indicates that the π-electronic conjugation in the excited singlet (S1) state is terminated at the acyl group and that the benzamide moiety in 1b has little effect on modulating the florescence color. The similar fluorescence solvatochromism of 1a–c reveals that their S1 states have a similar intramolecular charge transfer character. The fact that 1a–c have various fluorescence quantum yields and lifetimes depending on solvent polarity and hydrogen bonding interactions in solutions provides information about the decay processes competing with the fluorescence process in the S1 states. Among 1a–c, benzamide 1b exhibits the most sensitive variation of the fluorescence intensity depending on the solvent used. Similarity of the fluorescence spectra of 1a–c adsorbed in NaY zeolites was also observed, which indicates that the S1 states of 1a–c give mobile conformers in the NaY supercages. The relationship between the molecular structures of 1a–c and their spectroscopic properties will provide a guide for designing a new fluorophore based on Cypridina oxyluciferin.
An investigation of the chemiluminescent properties of 2,6-diphenylimidazo[1,2- a]pyrazin-3(7 H)-one derivatives (1), having substituted phenyl groups, is described. Among the derivatives 1, the 6-[4-(dimethylamino)phenyl] derivatives (1a,d–f) gave a high quantum yield (ΦCL ≥ 0.0025) in diglyme/acetate buffer, which is a model reaction condition for the Cypridina bioluminescence. Their efficient chemiluminescence is mainly caused by the electronic effect of the substituent at C6. In particular, the electron-donating 4-(dimethylamino)phenyl group at C6 of 1a,d–f plays an essential role in increasing the chemiexcitation efficiency (ΦS) by the charge transfer-induced luminescence (CTIL) mechanism. The results provide useful information for designing new Cypridina luciferin analogues showing efficient chemiluminescence.
thiazolo[4,5-b]pyrazine (TPy) derivatives with the phenyl group at the C2 position were studied. TPys were readily prepared from the corresponding amidopyrazines, which have a similar fluorescent core to a bioluminescence light emitter, Cypridina oxyluciferin. It was found that the introduction of electron-donating (methoxy and dimethylamino) groups onto the 2-phenyl moiety of the TPy derivatives, as well