Two new C,N,N-type ligands (HL2 and HL3), containing a Cphenyl, a Npyridyl, and a Nimidazolyl donor, and their cycloplatinated complexes, [Pt(L2)Cl] (1), [Pt(L3)Cl] (2), [Pt(L2)(PPh3)]+ (3) and [Pt(L3)(PPh3)]+ (4), have been successfully synthesized and characterized. Spectroscopic and 3MLCT luminescent properties of these Pt(II) cyclometalated complexes were found to be pH dependent. This was attributed to the protonation/deprotonation of the acidic 1-imidazolyl-NH moieties on the ligands. All the cycloplatinated complexes (both protonated and deprotonated forms) possessed two-photon excitability with two-photon absorption cross-sections ranging from 6.0 to 30.0 GM (protonated forms) and from 16.2 to 24.9 GM (deprotonated forms). Copyright © 2012 The Royal Society of Chemistry.