The synthesis and photophysical study of (C/\N)Pt(II)Q complexes, where C/\N is a bidentate cyclometalating ligand and Q is 8-hydroxyquinoline or quinoline-8-thiol, are presented. The compounds were obtained as a single isomer with N atoms of the C/\N and Q ligands trans-coordinated to the Pt(II) center as shown by X-ray crystallography. These chromophores absorb intensely in the visible region and emit in the deep-red spectral region from a quinolate-centered triplet intraligand charge-transfer excited state. The emission maxima are in the range 675-740 nm, with the quantum yields and lifetimes of up to 0.82% and 5.3 mus, respectively, in deoxygenated organic solvents at room temperature. These complexes are efficient photosensitizers of singlet oxygen in air-saturated solutions, with yields up to 90%.