One- and two-photon photophysical properties of the cyanuric chloride derivatives, 2-(4'-N,N-diethylamino)phenyl-4,6-dichloro-1,3,5-triazine (PDT) and 2-(3',5'-dimethyl-4'-N,N-diethylamino)phenyl-4,6-dichloro-1,3,5-triazine (MPDT), were investigated. Compared to PDT, the methyl substitutes in MPDT caused drastic reduction in molar extinction coefficient, fluorescence quantum yield and two-photon absorption cross-section (delta(TPA)), and induced significant increase in Stokes shift. An optically forbidden but two-photon allowed S-2 state with prominent intra-molecular charge-transfer character is found to be responsible for the two-fold larger delta(TPA) of PDT (188 GM at 800 nm) than that of MPDT (94 GM at 780 nm). The methyl substitutes in MPDT considerably enhance the S-1-state contribution to its delta(TPA), while the steric hindrance does not significantly destroy the conjugation between the electron lone pair of N1 and the aromatic pi-electrons. (C) 2007 Elsevier B.V. All rights reserved.