Investigating the Properties of Triangle Terthiophene and Triphenylamine Configured Propeller-like Photochromic Dye with Ethyne Bridge.

Synthesis-oriented design led us to the construction of a propeller-like dye, containing the triangle terthiophene and triphenylamine units. It reveals typical photochromic properties with alternated UV (390 nm) and visible light (˃ 440 nm) irradiation and the dye solution (in THF) color was also toggled between yellow-green and colorless. A new absorption band was observed in visible region (415-600 nm). Additionally, the photochromic dye was highly emissive with the absolute quantum yield being 0.27. After UV light irradiation, the emission was quenched significantly (Φ = 0.08) at photo-stationary state, and thus establishing a switchable emission "on-off" system by alternated UV/visible light irradiation cycle. Detailed structural analysis was carried out based on the optimized dye structure. Both the antiparallel conformation and the distance of reactive carbon atoms (< 4.2 Å) led to the smoothly photochromic behavior.

Photo-Induced Fluorochromism of a Star-Shaped Photochromic Dye with 2,4-Dimethylthiazole Attaching to Triangle Terthiophene.

A photochrmic triangle terthiophene dye with 2,4-dimethylthiazole attached was synthesized and shows regular photochromic properties when irradiated with UV/Vis light alternately. It was found that the attaching of 2,4-dimethylthiazole has a significant effect on both the photochromism and fluorescence of triangle terthiophene. During the photocyclizatioin prcess, not only the color but also the fluorescence of the dye in THF can be toggled between ring-open and ring-closed forms of the dye. Additionally, the absolute quantum yields (AQY) of ring-open and ring-closed forms of the dye (0.32/0.58) were greatly larger than the literature report. Along with the 254 nm light irradiation, the fluorescence color changed from deep blue (428 nm) to sky blue (486 nm) in THF. A fluorochromism cycle could be established based on the UV/visible light irradiation cycle, which provides a strategy for the design of new type fluorescent diarylethene derivatives for biological application.

Investigation of Triangle Terthiophene and Hydroxyphenylbenzothiazole Configured Fluorescent Dye with a Triple Bond Bridge.

A photochromic dye was constructed by incorporation of a carbon-carbon triple bond spaced triangle terthiophene skeleton and hydroxyphenylbenzothiazole. Regular photochromic behavior was investigated with alternated UV (254 nm) and visible light (≥ 400 nm) irradiation. The color of dye in solution can be cycled between pink and colorless. Additionally, the dye solution strongly fluoresces in THF with the absolute quantum yield (QY) being 0.56. When irradiation with 254 nm light, the emissive solution can be effectively quenched to photo-stationary sate (Φ = 0.05). An emission "on-off" cycle could be established based on the UV/visible light irradiation cycle. The photochromic dye also exhibits good photo- and thermal-stability at room temperature. The emission decay profile indicates typical single component character with the fluorescence lifetime being 6.68 ns. The emission color was determined by the CIE 1931 coordinates of x = 0.14, y = 0.25 in the blue region.

Investigating the Properties of Double Triangle Terthiophene Configured Dumbbell-Like Photochromic Dye with Ethyne and 1,3-Butadiene Bridge.

Dumbbell-like photochromic dyes were constructed by incorporation of double triangle terthiophene with ethyne or 1,3-butadiene bridge. Regular photochromic behavior was investigated with alternated UV (365 nm) and Visible light (˃ 400 nm) irradiation. However, the different bridge group leads to distinct difference in their photochromic wavelength. For the ethyne bridged triangle terthiophene (DT1), the photochromic wavelength was observed around 500-700 nm (peak value: 605 nm) and the solution turned to red with 365 nm light irradiation. However, the photochromic wavelength was blue shift to 418-550 nm and the solution was turned to light yellow for 1,3-butadiene bridged dye (DT2). Both of the colored solution can be bleached via visible light irradiation. Additionally, the two dyes in THF were emissive with absolute quantum yield (QY) of 0.36/0.40. Along with the photo-induced photocyclization process, the emissive solution can be effectively quenched at photo-stationary sate (Φ = 0.05/0.04). And emission "on-off" cycle could be established based on the UV/visible light irradiation cycle.