Hydrophobic Chromophores in Aqueous Micellar Solution Showing Large Two-Photon Absorption Cross Sections

A series of new hydrophobic two‐photon absorbing (2PA) chromophores with varied electron‐donating groups in quasi‐linear and multibranched structures are synthesized to correlate their structure/photophysical property relationships. The feasibility of using these large two‐photon absorption cross‐sectional (δ, expressed in GM = 1 × 10–50 cm4 s photon–1 molecule–1) materials in aqueous solution is also explored. All four hydrophobic 2PA materials can be encapsulated into micelles generated by dispersing an amphiphilic block copolymer, poly(methacrylic acid)‐block‐polystyrene (PMAA‐b‐PS), into water. The micellar nanostructures are characterized using dynamic light scattering, atomic force microscopy, and transmission electron microscopy. After these dyes are incorporated into micelles, they exhibit strong fluorescence in water. It is found that the quantum yield and δ values of these chromophores are strongly dependent on the diameters of the micelles, concentrations of the PMAA‐b‐PS, and molecular structures of the 2PA chromophores. One of the compounds that has a strong triarylamino donor and a multibranched structure exhibits a large δ value of 2790 GM and high quantum yield (0.56) in micelle‐containing water. Although this value is smaller than the original value of 5300 GM in toluene, it is still substantially larger than the values of most water‐soluble 2PA materials, which have δ values of less than 100 GM. Micelles derived from an amphiphilic block copolymer are demonstrated to be efficient nanocarriers to encapsulate highly efficient, hydrophobic, two‐photon‐absorbing chromophores into aqueous solutions. A large two‐photon cross section (δ) up to 2790 GM is achieved in aqueous solution, which is more than one order of magnitude higher than most of the hydrophilic 2PA materials that have δ values of less than 100 GM.