Substituent Effect at the C4-Position of 1,3a,6a-Triazapentalene.

Various 2,4-disubstituted-1,3a,6a-triazapentalenes possessing methyl and phenyl groups at the C4-position were synthesized. Fluorescence observation of the synthetic 4-methyl- and 4-phenyl-1,3a,6a-triazapentalenes revealed that the introduction of a substituent at the C4-position allowed a long-wavelength shift of the fluorescence maximum. Furthermore, the phenyl group at the C4-position was found to induce a substantial increase in the extinction coefficient value.

Synthesis of yellow and red fluorescent 1,3a,6a-triazapentalenes and the theoretical investigation of their optical properties.

To expand the originally developed fluorescent 1,3a,6a-triazapentalenes as fluorescent labelling reagents, the fluorescence wavelength of the 1,3a,6a-triazapentalenes was extended to the red color region. Based on the noteworthy correlation of the fluorescence wavelength with the inductive effect of the 2-substituent, electron-deficient 2-(2-cyano-4-methoxycarbonylphenyl)-1,3a,6a-triazapentalene and 2-(2,6-dicyano-4-methoxycarbonylphenyl)-1,3a,6a-triazapentalene were synthesized. The former exhibited yellow fluorescence and the latter exhibited red fluorescence, and both compounds exhibited large Stokes shifts, and the 1,3a,6a-triazapentalene system enabled the same fluorescent chromophore to cover the entire region of visible wavelengths.

One-pot synthesis of highly fluorescent 2,5-disubstituted-1,3a,6a-triazapentalene.

A one-pot synthetic method was established for the preparation of 2,5-disubstituted-1,3a,6a-triazapentalenes. The fluorescence observation of the synthetic 2,5-disubstituted-1,3a,6a-triazapentalenes revealed that the introduction of a substituent at the C5 position allowed a substantial change in the fluorescence quantum yield with little effect on the fluorescence wavelength.