Optical properties of a two-photon chromophore in a polymeric nanostructure

Optical properties of a cationic two-photon absorption (TPA) chromophore, 1,4-bis{4′-[N,N-bis(6′′-trimethylammoniumhexyl)amino]styryl} benzene tetrabromide (C1) upon complexation with an anionic diblock copolymer, poly[(ethylene oxide)-block-(sodium 2-acrylamido-2-methyl-1-propane sulfonate)] (E _m-A _n) and a cationic surfactant, cetyltrimethylammonium bromide (CTAB) have been studied. Electrostatic interaction among C1, cationic CTAB and anionic (E _m-A _n) forms a vesicular polymeric nanostructure (containing C1 in a core), which is soluble in water. Incorporation of C1 into the nonpolar microenvironment inside the nanostructure successfully modulated its optical properties in aqueous medium. In water, fluorescence quantum yield (η) of C1 (0.32) was increased up to 0.55 accompanied with 30∼40 nm PL photoluminescence (PL) spectral shifts by forming the self-assembled nanostructure. This vesicular nanostructure may have a potential application as a two-photon molecular tag for biological imaging by two-photon microscopy.