Photophysical and Photochemical Features of Lysine Derivatives Bearing Two Triphenylaminocinnamic-Based Fluorophores

A Morita-Baylis-Hillman adduct (MBHA) derivative bearing a triphenylamine (TPA) moiety was previously found to react with Nα-acetyl-l<i>-</i>lysine methyl ester with the formation of the corresponding diadduct derivative as the major reaction product and a monoadduct as the minor one. The characterization of photochemical features of the diadduct bearing two triphenylaminocinnamic (TPAC) fluorophores suggested that this compound shows the tendency to undergo the [2 + 2] photocycloaddition reaction. This hypothesis was evaluated in the present study in both the diadduct derivatives obtained with Nα-acetyl-l-lysine methyl ester and Nα-acetyl-l-lysine. The hypothesis was confirmed in the case of the diadduct derivative obtained from Nα-acetyl-l-lysine methyl ester, whereas the UV-A irradiation of the diadduct derivative obtained from Nα-acetyl-l-lysine led to the formation of a strongly emissive (QY = 69%, λ_em = 460 nm) symmetric dimer.