Extended Alkenyl and Alkynyl Benzotriazoles with enhanced Two‐Photon Absorption properties as a promising alternative to Benzothiadiazoles

A series of donor-pi-acceptor-pi-donor (D-pi-A-pi-D) benzoazole dyes with 2H-benzo[d][1,2,3]triazole or BTD cores have been prepared and their photophysical properties characterized. The properties of these compounds display remarkable differences, mainly as a result of the electron-donor substituent. Dyes with the best properties have visible-light absorption over lambda=400 nm, large Stokes shifts in the range of about 3500-6400 cm(-1) , and good fluorescence emission with quantum yields of up to 0.78. The two-photon absorption properties were also studied to establish the relationship between structure and properties in the different compounds synthesized. These results provided cross sections of up to 1500 GM, with a predominance of S2 <--S0 transitions and a high charge-transfer character. Time-dependent DFT calculations supported the experimental results.