Spectroscopic and theoretical studies on the photophysical properties of dichlorotriazine derivatives

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 (δTPA), and induced significant increase in Stokes shift. An optically forbidden but two-photon allowed S2 state with prominent intra-molecular charge-transfer character is found to be responsible for the two-fold larger δTPA of PDT (188 GM at 800 nm) than that of MPDT (94 GM at 780 nm). The methyl substitutes in MPDT considerably enhance the S1-state contribution to its δTPA, while the steric hindrance does not significantly destroy the conjugation between the electron lone pair of N1 and the aromatic π-electrons.