Excited-state absorption and anisotropy properties of two-photon absorbing fluorene derivatives

The electronic structure of fluorene derivatives N-(7-benzothiazol-2-yl-9,9-bis-decyl-9H-fluoren-2-yl)-acetamide (1); 9,9-didecyl-2,7-bis-(N,N-benzothiazoyl)fluorene (2); 4,4′-{[9,9-bis(ethyl)-9H-fluorene-2,7-diyl]di-2,1-ethenediyl}bis(N, N-diphenyl)benzeneamine(3); and4,4′,4″([9,9-bis(ethyl)-9H-fluorene-2,4,7-triyl]tri-2, 1-ethenediyl}tris(N,N-diphenyl)benzeneamine (4) were investigated by a steady-state spectral technique, quantum-chemical calculations, and a picosecond pump-probe method. These derivatives are of interest for their relatively high two-photon absorption. The steady-state excitation anisotropy spectra reveal the nature of the ground-state absorption bands. Semiempirical quantum-chemical calculations of the fluorene derivatives (AMI, ZINDO/S) show good agreement with experimental data. The spectral positions and alignment of various electronic transitions of derivatives 1-4 were estimated from their excited-state absorption and anisotropy spectra.