We have investigated the spectral characteristics, quantum yield ϕF, lifetime τF, and polarization of fluorescence of NH-isomers of dibenzobarrelene disubstituted tetraazaisobacteriochlorin at 293 and 77 K. The following information has been obtained from low-temperature measurements: 1) the weak shoulder on the edge of the long-wavelength 0-0 absorption band disappears at 77 K and, therefore, can be assigned to the cis-NH-isomer [the principal component of the tautomeric mixture is the trans-isomer a (b)]; 2) the low value of ϕF at room temperature is due to temperature-viscosity quenching whereas ϕF at 77 K is close to 1 and τF = 5.3 nsec; 3) the energy of the weak electronic transition G → Q2 and the interval $$\Delta E_{Q_2 } E_{Q_1 } \approx 2750 cm^{ - 1} $$ have been determined. Quantum-chemical calculations found that replacing the methine bridges by nitrogen stabilizes the non-aromatic trans-isomer a (b) whereas the non-planarity of the macrocycle and the alternation of bond lengths increase for the cis-isomers. The calculated electronic absorption spectra of the a isomer reproduce rather well the experimental data. It is shown that the four-orbital model is applicable for the lower excited states Q1 and Q2 for all NH-isomers.