Strongly red-fluorescent novel donor–π-bridge–acceptor–π-bridge–donor (D–π–A–π–D) type 2,1,3-benzothiadiazoles with enhanced two-photon absorption cross-sections

Novel donor–π-bridge–acceptor–π-bridge–donor (D–π–A–π–D) type 2,1,3-benzothiadiazole fluorescent dyes connected to the N,N-diarylamino terminus via various type π-conjugate spacers exhibits large two-photon absorption cross-sections and high fluorescent quantum yields in orange-red color.