Aggregation-enhanced fluorescence and two-photon absorption in nanoaggregates of a 9,10-Bis[4′-(4″-aminostyryl)styryl]anthracene derivative

This paper reports the design, synthesis, and theoretical modeling of two-photon properties of a new class of chromophore that exhibits enhanced two-photon absorption (TPA) and subsequently generated strong up-converted emission in nanoaggregate forms. This chromophore utilizes the basic structural unit of 9,10-bis[4′-(4″-aminostyryl)styryl]anthracene that exhibits large internal rotation in the monomer form in organic solvents, whereby the fluorescence is greatly reduced. In nanoaggregates formed in water, the internal rotation is considerably hindered, leading to significant increases of TPA and fluorescence quantum yield. Theoretical modeling of the conformational structure and dynamics has utilized a semiempirical pm3 formalism. The TPA cross sections of the monomer and the aggregate states have been calculated on the basis of the quadratic response theory applied to a single-determinant self-consistent field reference state making use of a split-valence 6-31G* basis set.