  The electronic structure of chair-type biphenylene ribbons is studied within
the framework of the Hubbard Hamiltonian in the approximation of static
fluctuations. An expression is obtained for the Fourier transform of the
Green's functions, whose poles determine the spectrum of elementary
excitations. The energy spectrum of biphenylene ribbons indicates that
nanoribbons with a width of 6, 9, 12, 15, 18 carbon atoms are in the
semiconductor state. Densities of state of electrons of biphenylene ribbons of
various widths are presented in comparison with the results of experimental
measurements of differential conductance of biphenylene ribbons. It is shown
that the width of the band gap decreases exponentially with an increase in the
width of the biphenylene ribbon. Ribbons with a width of 21 carbon atoms or
more are in the metallic state.
