Synthesis of Thiazoles Bearing Aryl Enamine/Aza‐enamine Side Chains: Effect of the π‐Conjugated Spacer Structure and Hydrogen Bonding on Photophysical Properties

Abstract

An efficient synthesis of a new series of di‐ and trisubstituted thiazoles (TZs) bearing aryl enamine side‐chains (ETZs) has been developed and the optical properties of these compounds compared with structural analogues containing the isoelectronic aza‐enamine group (ATZs). Spectral characterization demonstrated the difference in the absorption and fluorescence of the ETZs and ATZs in solution and the emergence of fluorescent ETZs in the solid state. The optimized structural geometries and weak intramolecular interactions, electronic characteristics of the ground and excited states, HOMO and LUMO analyses, changes in electron density after S0 → S1v excitation and maps of electrostatic potential (MEPs) calculated by means of DFT have allowed us to estimate the particularities of the geometric and electronic structures of the ETZs and ATZs in the ground and excited states. The availability, synthetic simplicity, stability, large Stokes shifts and high sensitivity to the microenvironment (fluorosolvatochromic behaviour) make the obtained TZs a useful platform for the further design and synthesis of new effective compounds for applications in the field of fluorescence imaging.

Synthesis and Photophysical Properties of 5-N-Arylaminothiazoles with Sulfur-Containing Groups on the Aromatic Ring at the 2-Position

“…The residue was purified by column chromatography (SiO2, hexane : EtOAc = 1 : 1.5) to give the thiazole 9a (0.19 g, 83%) as a yellow solid; mp 185-187 °C; 1 H NMR (CDCl3)  2.75 (s, 3H), 7.00 (d, J = 5.9 Hz, 2H), 7.12 (d, J = 5.9 Hz, 5H), 7.23 (d, J = 7.36 Hz, 6H), 7.70 (d, J = 7.32 Hz, 2H), 7.93 (d, J = 6.88 Hz, 2H), 8.11 (d, J = 8.24 Hz, 2H); 13 C NMR (CDCl3)  43.8 (S(=O)CH3), 121. 4,123.3,124.0,126.9,127.4,128.1,128.2,129.2,133.0,136.4,140.9,146.3,147.1,161.3;MS (EI) 3, 44.5, 120.5, 122.1, 123.1, 124.7, 126.0, 126.4, 127.6, 128.1, 129.0, 129.7, 13.04, 130.6, 132.5, 136.5, 137.8, 140.8, 144.3 44.5,121.6,123.5,126.8,127.4,128.0,128.3,129.3,129.5,132.9,138.7,141.0,142.0,146.3,149.2,160.2;MS (EI) 13 C NMR (CDCl3)  20. 7,21.3,44.5,120.4,121.0,121.5,121.6,125.8,126.2,126.7,126.9,127.0,127.3,127.9,128.8,129.0,129.4,…”

“…4,123.3,124.0,126.9,127.4,128.1,128.2,129.2,133.0,136.4,140.9,146.3,147.1,161.3;MS (EI) 3, 44.5, 120.5, 122.1, 123.1, 124.7, 126.0, 126.4, 127.6, 128.1, 129.0, 129.7, 13.04, 130.6, 132.5, 136.5, 137.8, 140.8, 144.3 44.5,121.6,123.5,126.8,127.4,128.0,128.3,129.3,129.5,132.9,138.7,141.0,142.0,146.3,149.2,160.2;MS (EI) 13 C NMR (CDCl3)  20. 7,21.3,44.5,120.4,121.0,121.5,121.6,125.8,126.2,126.7,126.9,127.0,127.3,127.9,128.8,129.0,129.4,129.7,129.9,130.2,132.9,144.3,165.2;MS (EI)…”

“…In contrast, we have focused on monocyclic aromatic compounds that have thiazole cores. 4 In particular, we recently established synthetic methods for compounds with N-arylamino groups at the 5-position of thiazoles 5 in a series on main group chemistry. 6 We also determined their fundamental photophysical properties 5b and used them in white-light emission, 7 the generation of radical cations showing near-infrared absorption, 8 and the detection of halogenated solvents via vapochromic behaviors.…”

Asymmetric Dual‐State Emitters Featuring Thiazole Acceptors

“…Remarkable examples can be found in the reports of Huang, [9] Belskaya, [10] Murai, [11] and Nallagondu, [12] in which they have explored thiazoles with different substituents, substitution patterns, and varying length of the conjugated fluorophore skeleton, with the resulting emission ranging from 390 nm to 726 nm. [9,13] Some of these thiazole derivatives have been used in WOLEDs, [14] solar cells, [15] OFETs, and OPVs. [16] It is also important to mention that most synthetic methods afford either 2,4,5-trisubstituted [10,17] or 2,4-disubstituted thiazoles, [18] and that fluorophores with 2,5-disubstituted thiazoles are very scarce, with some notable examples reported as DSEgens.…”

Two Approaches for the Synthesis of Fused Dihydropyridines via a 1,6-Electrocyclic Reaction: Fluorescent Properties and Prospects for Application

“…Thioamides are building blocks widely used for the synthesis of nitrogen- and sulfur-containing heterocyclic compounds. − Thioamides can react with various monoelectrophilic, dielectrophilic, and ambient agents, such as α-halocarbonyl compounds and alkyl and alkenyl dihalides. − The CS bond of a thioamide group may react as a dienophile component in [4 + 2] cycloaddition reactions − and as a dipolarophile in the thermal and catalytic variants of 1,3-dipolar cycloaddition reactions. ,, Moreover, α-diazothioacetamides easily transform into 1,2,3-thiadiazoles by a 1,5-electrocyclic reaction. ,− …”