title: Novel 2,1,3-benzothiadiazole-based red-fluorescent dyes with enhanced two-photon absorption cross-sections.
abstract: This paper reports the two-photon absorbing and orange-red fluorescence emitting properties of a series of new 2,1,3-benzothiadiazole (BTD)-based D-pi-A-pi-D-type and star-burst-type fluorescent dyes. In the D-pi-A-pi-D-type dyes 1-6, a central BTD core was connected with two terminal N,N-disubstituted amino groups via various pi-conjugated spacers. The star-burst-type dyes 8 and 10 have a three-branched structure composed of a central core (benzene core in 8 and triphenylamine core in 10) and three triphenylamine-containing BTD branches. All the BTD-based dyes displayed intense orange-red color fluorescence in a region of 550-689 nm, which was obtained by single-photon excitation with good fluorescent quantum yield up to 0.98 as well as by two-photon excitation. Large two-photon absorption (TPA) cross-sections (110-800 GM) of these BTD dyes were evaluated by open aperture Z-scan technique with a femtosecond Ti/sapphire laser. The TPA cross-sections of D-pi-A-pi-D-type dyes 2-6 with a benzene, thiophene, ethene, ethyne, and styrene moiety, respectively, as an additional pi-conjugated spacer are about 1.5-2.5 times larger than that of 1c with only a benzene spacer. The TPA cross-sections significantly increased in three-branched star-burst-type BTDs 8 (780 GM) with a benzene core and 10 (800 GM) with a triphenylamine core, which are about 3-5 times larger than those of the corresponding one-dimensional sub-units 9 (170 GM) and 11 (230 GM), respectively. The ratios of sigma/e(pi) between three-branched and one-dimensional dyes were 6.5:3.8 (for 8 and 9) and 6.0:4.0 (for 10 and 11), which are larger than those predicted simply on the basis of the chromophore number density (1:1), according to a cooperative enhancement of the two-photon absorbing nature in the three-branched system.
authors.affiliation: Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, 6-1 Kasuga-koh-en, Kasuga 816-8580, Japan.
authors.forename: Shin-ichiro
authors.initials: S
authors.lastname: Kato
authors.forename: Taisuke
authors.initials: T
authors.lastname: Matsumoto
authors.forename: Motoyuki
authors.initials: M
authors.lastname: Shigeiwa
authors.forename: Hideki
authors.initials: H
authors.lastname: Gorohmaru
authors.forename: Shuuichi
authors.initials: S
authors.lastname: Maeda
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Ishi-i
authors.forename: Shuntaro
authors.initials: S
authors.lastname: Mataka
mesh_terms: D003116:Color; D005456:Fluorescent Dyes / Q000737:chemistry*; D015394:Molecular Structure; D010777:Photochemistry; D017785:Photons; D013830:Thiadiazoles / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D013830:Thiadiazoles; C015700:benzo-1,2,3-thiadiazole