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.

Selective Tuning of the HOMO–LUMO Gap of Carbazole‐Based Donor–Acceptor–Donor Compounds toward Different Emission Colors

“…[25] All the compounds give relatively high fluorescence quantum yields (Φ PL ) in dichloromethane solution: 0.6 for 1, 0.55 for 2, 0.30 for 3, and 0.35 for 4 (Rhodamine B as the standard, Φ PL = 0.65 in ethanol). [3] Figure 4. Room-temperature uncorrected emission spectra of 3 and 4 in heptane, dioxane, THF, dichloromethane, and MeCN at 1 ϫ 10 -6  (λ ex 3: 412 nm; 4: 450 nm).…”

“…[3,4] The EL and NLO performances of these molecules are effectively dependent on their HOMO-LUMO or band gaps associated with intramolecular D-A interactions. The strength of D-A interactions is determined by donor and acceptor groups and the connecting π bridges.…”

A New Series of Quadrupolar Type Two‐Photon Absorption Chromophores Bearing 11, 12‐Dibutoxydibenzo[a,c]‐phenazine Bridged Amines; Their Applications in Two‐Photon Fluorescence Imaging and Two‐Photon Photodynamic Therapy

“…The red shift of the charge transfer band in 6 compared to 4 and 7 is consistent with the trend observed for 2,1,3-benzothiadiazole-based D-A-D type compounds. [18,19] Apparently, the non-coplanarity between phenylene and phenazine in 4 results in less effective interaction between the donor and the acceptor. Relative to the para-substitution in 6, the metasubstitution of the peripheral diphenylamines in 7 seems to deconjugate [20] the effective interaction between the amines and the phenazine.…”

Photophysical Properties of Two New Donor-Acceptor Conjugated Copolymers and Their Model Compounds: Applications in Polymer Light Emitting Diodes (PLEDs) and Polymer Photovoltaic Cells (PPCs)

“…Through this study, it is found that the calculated results reproduce very well the corresponding experimental data [87]. In order to study the emission properties of P3HT2BTCz compounds, the TD/B3LYP method was applied to the geometry of the lowest singlet excited state optimized at the CIS level with 3-21G* basis set [124]. The normalized photoluminescence (PL) spectrum of P3HT2BTCz (Fig.…”