Two-Photon-Excited Fluorescent Tetrabranched Triphenylborane Featuring the Cooperative Effect of Branching in Two-Photon Absorption

We here disclose a new type of two-photon-excited fluorescent triarylborane, tetrabranched triphenylborane 1, which contains four electron-donating [4-(N,N-diphenylamino)­phenyl]­ethynyl branches at 2,6-positions of two phenyl rings. The cross section of 1 reaches 275 GM (1 GM = 10⁻⁵⁰ cm⁴ s photon⁻¹) in tetrahydrofuran. Compared with dibranched triphenylborane 2, the 2-fold increase in the number of electron-donating branches induces a 3.6-fold increase in the two-photon absorption cross section, suggesting the great cooperative effect of branching in the enhancement of two-photon absorption.