•We designed and synthesized two novel carbazole-based dye molecules.•The dye D4 containing thiophene group showed better photoelectronic and photovoltaic properties than D3.•The two dyes could be applied as sensitizers in nano-TiO2 DSSCs.Two carbazole-based dye molecules: 3-(6-benzothiazol-2-yl-9H-hexylcarbazole-3-yl)-2-cyano-acylic acid (D3) and 3-[5-(6-benzothiazol-2-yl-9H-hexylcarbazole-3-yl)-thiophen-2-yl]-2-cyan-acylic acid (D4) were synthesized by an approach from carbazole derivate using Vilsmeier-Haack, Suzuki cross-coupling and Knoevenagel reactions. Their physical and electrochemical properties were investigated. D3 and D4 exhibit different optical properties, such as UV absorption, photoluminescence, fluorescence quantum yield and fluorescence lifetime in different solvents. Compared with D3 without a thiophene unit, the maximum absorption wavelength of D4 red-shift obviously and its fluorescence intensity is also enhanced. A shift of the EHOMO and ELUMO is observed for D3 (EHOMO = 2.06 V, ELUMO = −1.39 V vs. NHE) and D4 (EHOMO = 1.73 V, ELUMO = −1.33 V vs. NHE). D3 and D4 can be used as dyes for dye-sensitized solar cells (DSSCs) with TiO2 nanomaterial because their EHOMO are lower than the conduction band edge of TiO2 [−0.5 V (vs. NHE)] and their ELUMO are higher than the I3−/I− redox potential [0.42 V (vs. NHE)].

A new carbazole-based Schiff-base (1) as a multi-functional fluorescent chemosensor was designed, synthesized and characterized, which can selectively recognized Fe3+ and Cu2+ ions over a number of other metal ions. Compound 1 could detect Fe3+ and Cu2+ by UV–Vis method and fluorescence method. The stoichiometry ratio of 1-Fe3+ and 1-Cu2+ are 2:1 and 1:1, respectively, by the method of Job’s plot. Moreover, the detection limits were calculated to be 4.23 × 10−6 mol/L for Fe3+ ion and 5.67 × 10−6 mol/L for Cu2+ ion. In the presence of Fe3+/Cu2+ ions, the fluorescence enhancement was attributed to the inhibited CN isomerization and the obstructed excited state intramolecular proton transfer (ESIPT) of compound 1. At the same time, the interactions of compounds 1 with other ions were also investigated and unobvious UV–Vis absorption and fluorescence spectral changes were observed. Thus a new kind of chemosensor for Fe3+/Cu2+with high sensitivity and selectivity was introduced.Graphical abstractHighlights► We designed and synthesized a new carbazole-based Schiff base sensor. ► Compound 1 could be used as a multi-functional sensor for detecting Fe3+/Cu2+ by both using UV–Vis and fluorescence methods. ► We found that the bonding mode between compound 1 and Fe3+/Cu2+ is different.