It is well known that pristine graphitic carbon nitride (g-C3N4) exhibits low carrier mobility and low visible response, thus hindering its application to some extent. The derivatization on g-C3N4 derivatives is the way to tune its band gap and thus modify its electronic and optical properties. In present work, the geometric, electronic and optical properties of g-C3N4 and its derivatives (C6N7)(n), [C6N7(C-2)1.5](n), [C6N7(C-4)(1.5)](n), [C6N7(C3N3)](n) and [C6N7(N-2)1.5](n) were investigated by first-principles calculations. Compared to g-C3N4, the band gaps of five carbon nitride derivatives decrease. The work function of carbon nitrides derivatives are larger than g-C3N4. The strong absorption peak of g-C3N4 is around 350 nm, while the absorption spectra extents of five carbon nitride derivatives increase, the absorption wavelength ranges extend to the visible region. For five carbon nitride derivatives, the HOMOs and LUMOs show significant delocalization compared to that of g-C3N4, which are helpful to facilitate the enhancement of carrier mobility. It infers that the photogenerated e /h(+) pairs in five carbon nitride derivatives effectively separate, which can improve the photocatalytic efficiency. The present results are expected to give a guide for design and application of the g-C3N4 derivatives in further experimental and theoretical investigations. (C) 2018 Elsevier B.V. All rights reserved.