| Abstract |
Bis(dioxaborine) dyes of the A-pi-A format (A: acceptor, pi: conjugated bridge) were prepared and photophysically characterized. The best performing dyes feature (a) visible-light absorption (>400 nm), (b) high molar absorption coefficients (up to 70000 (-1)(M) cm(-1)), (c) Stokes shifts in the range of ca. 2500-5800 cm(-1), and (d) strong fluorescence emission with quantum yields of up to 0.74. This yields very bright-emitting dyes for one-photon excitation. However, the most intriguing feature of the dyes is their strong two-photon absorption. This was achieved by means of increased pi-conjugation in the phenylene or phenylene-thiophene bridges through the variation of the conjugation length and rigidity. This provided two-photon absorption cross sections of up to 2800 GM (1 Goeppert-Mayer (GM)= 10- 50 cm(4)sphoton(-1)). Considering the mentioned high fluorescence quantum yields, exceptionally bright-emitting A-pi-A two-photon absorbing dyes with low molecular mass are obtained. Time-dependent density-functional theory calculations corroborated the experimental results. |
