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4-Ethoxy-2-(pyridin-2-yl)-5-(3,4,5-trimethoxyphenyl)thiazole (EPTT) was prepared in a four-step synthetic protocol. Column shaped single crystals of EPTT were obtained from a saturated EtOH solution. Both single crystals and a THF solution of EPTT were investigated in terms of their photophysical properties and electronic structure. The crystals showed very intense fluorescence upon photoexcitation as well as a red shifted emission maximum compared to a THF solution of EPTT (single crystals: λem = 523 nm, ΦFL = 0.82, THF solution λem = 477 nm, ΦFL = 0.67). Quantum chemical methods were then employed to unravel the underlying fundamental transitions and explain the experimental results. Calculations for a small dye cluster modeled after the x-ray crystal structure predicted three dark intermolecular CT states, S1-S3, below the intramolecular CT state (S4) for EPTT in the crystalline state. Photoexcitation and subsequent relaxation along the excited states relaxation pathways may populate the low-lying dark intermolecular CT states, which in consequence leads to an exciton moving along the stacked dyes in the crystal. This finding explains the significantly enhanced red-shift of the solid-state fluorescence of EPTT compared to the dissolved dye.

A small library of N,N-diethyl- and -diethanolsulfonamides of differently substituted 2-(2-pyridyl)- and 2-pyrazinyl-4-alkoxythiazoles has been synthesized and investigated in terms of their photophysical properties, electronic structure (quantum chemical calculations at the CAM-B3LYP/6-31+G(d,p) level of theory) and thin film morphology (Langmuir–Blodgett- and spin-cast films). By using the Langmuir–Blodgett technique we show how to exert direct control over the degree of aggregation in thin films made from different thiazole type dyes. In combination with spectroscopic investigations, we gained an in-depth understanding of the influence of aggregation on the electro-optical properties of thin films made of the here-investigated substances.

A series of donor-π-acceptor (D-π-A) substituted 4-hydroxythiazoles have been synthesized. Electron-donating groups (4-methoxyphenyl and 4-dimethylaminophenyl) were installed in the 5-position of the thiazole; thiophene/pyridine-bridged acceptors (formyl groups and their Knoevenagel condensation products) were placed in the 2-position. The influence of D-π-A character on the photophysical properties and electronic structure was investigated by means of UV/Vis and fluorescence spectroscopy.

A series of four donor aryl alkynyl substituted thiazole derivatives 3a-d and three similar aryl donor-acceptor systems 6a-c have been synthesized. All compounds bear different electron-donating groups in the 5-position of the thiazole core. The influence of both electron donor strength and the additional phenylethynyl unit on photophysical properties, i.e. UV/Vis absorption, fluorescence emission and fluorescence lifetime, has been evaluated. Additionally, theoretical calculations have been performed at the CAM-B3LYP/6-31+G(d,p) level and good agreement with the experimental data has been achieved. The new derivatives synthesized via palladium catalyzed cross coupling are characterised by moderately strong emission between 474 and 538 nm (ΦF = 0.35-0.39) and Stokes' shifts ranging from 0.54 to 0.79 eV (4392-6351 cm(-1)). The smaller chromophores of type 6 exhibit modest to high fluorescence emission (ΦF = 0.45-0.76) between 470 and 529 nm and their Stokes' shifts range from 0.59 to 0.65 eV (4765-5251 cm(-1)).

Reported is a study on the influence of regioisomerism on the photophysical properties in 4-hydroxy-1,3-thiazole-based push–pull-chromophores/fluorophores to evaluate the molecular structure–property relationship as a basic foundation for future design strategies concerning this class of dyes. Surprisingly, the nitro groups used as acceptors do not act as a fluorescence quencher, instead the derivatives synthesized exhibit quantum yields of 37–40%. Two 4-ethoxy-1,3-thiazole derivatives which differ only in the positioning of their electron donating (methoxy) and electron withdrawing (nitro) groups have been synthesized and examined in terms of their photophysical properties, i.e. UV/Vis absorption and fluorescence emission spectra. Additionally, quantum chemical calculations have been performed to unravel the underlying fundamental transitions and to explain the experimental results.

Molecular probes are widely used tools in chemical biology that allow tracing of bioactive metabolites and selective labeling of proteins and other biomacromolecules. A common structural motif for such probes consists of a reporter that can be attached by copper(I)-catalyzed 1,2,3-triazole formation between terminal alkynes and azides to a reactive headgroup. Here we introduce the synthesis and application of the new thiazole-based, azide-tagged reporter 4-(3-azidopropoxy)-5-(4-bromophenyl)-2-(pyridin-2-yl)thiazole for fluorescence, UV and mass spectrometry (MS) detection. This small fluorescent reporter bears a bromine functionalization facilitating the automated data mining of electrospray ionization MS runs by monitoring for its characteristic isotope signature. We demonstrate the universal utility of the reporter for the detection of an alkyne-modified small molecule by LC–MS and for the visualization of a model protein by in-gel fluorescence. The novel probe advantageously compares with commercially available azide-modified fluorophores and a brominated one. The ease of synthesis, small size, stability, and the universal detection possibilities make it an ideal reporter for activity-based protein profiling and functional metabolic profiling.