The use of two-photon absorbing (TPA) chromophores for applications in photodynamic therapy (PDT) and fluorescence imaging provides many advantages. The non-linear properties make it possible to increase both observation depth in animals and 3D resolution. Nevertheless, for in vivo applications, improving biocompatibility of these inherently lipophilic chromophore is a challenge.

            The development of new chromophores for PDT-TPA using a molecular engineering approach using bromide substituents as singlet oxygen generators is described. Parameters like positions and numbers of bromide, conjugated length and chromophore symmetry are studied. The study shows the importance of bromide atom position and of the symmetry on the inter system crossing efficiency.

            During the engineering study, spectroscopic observations and rationalizations permit to envision the design of new chromophores for two-photon laser scanning fluorescent microscopy. The biocompatibility of these chromophores is provided by (hydroxyethyl)acrylate polymer, which provides a covalent water-soluble shell. These chromophores are used to make high resolution images of cerebral vascularization. One of these chromophores shows intravital specific interaction with endothelial cells in blood vessels. Applications of the chromophore are described.

            Strategies to increase the intravital selectivity of polymer/chromophores units towards cancer cells and tumors are presented. A modification of the hydroxyl function by imidazolium group is described. Complexation studies of polymer with DNA and in cellulo spectroscopic studies were performed.