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 cm 4 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.