Heterocyclic molecules with ESIPT emission: synthetic approaches, molecular diversities, and application strategies

Abstract

Excited-state intramolecular proton transfer (ESIPT) is one of the most essential emission processes in most circumstances because of its dual emission band in most cases and its high Stokes shifts. These distinguishing properties make ESIPT-based probes more suitable for a variety of applications, including analyte sensors, solid-state sensing mechanisms, optical technologies, and biomarkers for endogenous or exogenous compounds in various settings. As a result, researchers around the world are working on ESIPT emissions and developing different scaffolds for various applications or industry demands. This field of study is rapidly expanding and there is a need for an up-to-date review of synthesis methodologies and applications. This paper provides the highlights of ESIPT-based heterocyclic scaffolds, synthesis strategies, and application scenarios in the literature from 2017 to 2023.

Keywords: ESIPT emission; fluorescence; sensors; synthesis.

Figure 1

A) The most popular heterocycles for ESIPT emission; B) different substituents with different heterocycles for ESIPT emission; C) CIM and CIN structures for ESIPT emission.

Scheme 1

Proposed ESIPT mechanism.

Scheme 2

Imidazole-based probe for selective recognition for Fe³⁺.

Scheme 3

A) ESIPT-ON mechanism for Hg²⁺ and B) HOCl detection via a benzothiazole derivative.

Scheme 4

Detection of Mg²⁺ ions with benzimidazole derivatives having amine cavities.

Scheme 5

Design of a chemosensor with a propargyl group for detection of palladium ions.

Scheme 6

Sensing of Cu²⁺ ions with ESIPT-based phthalimide probe 21.

Scheme 7

Imine-based chemosensor for detection of CN ions.

Scheme 8

Synthesis of symmetric bisbenzoxazole-thiophene-diol and its derivatives for double ESIPT emission.

Scheme 9

Synthesis of ESIPT-based imidazole derivatives with dual emission.

Scheme 10

Synthesis of nitrile-substituted 2-(oxazolinyl)-phenols 34–37.

Scheme 11

Imidazole derivative for ESIPT emission and its detection mode for anions.

Scheme 12

Investigation of indole derivatives for possible ESIPT emission.

Scheme 13

Benzophenone derivatives 53–55 for ESIPT emission.

Scheme 14

N-Hydroxy imidazole derivatives for ESIPT emission.

Scheme 15

Benzoxazole derivative with alkyne units for ESIPT emission.

Scheme 16

Detection of biothiols with acrylate unit through ESIPT emission (Cys: cysteine, Hcy: homocysteine, GSH: glutathione).

Scheme 17

Synthesis of mitochondria-targeted chemosensor 67.

Scheme 18

Synthesis of compound 71 for ER tracking and detection of ONOO⁻.

Scheme 19

Synthesis of probe for detection of hydrogen sulfur in living media.

Scheme 20

Synthesis of probe 81 for peroxynitrite detection.

Scheme 21

Benzothiazole derivatives for chemosensors for the selective detection of HOCl.

Scheme 22

ESIPT-emitted flavonoid for detection of heptad-interfaced G-quadruplexes.

Scheme 23

Benzimidazole derivatives for HOCl detection.

Scheme 24

New ESIPT-based probe for thiol detection.

Scheme 25

Selective detection of thiols with an imidazo[1,5-α]pyridine derivative as a chemosensor.

Scheme 26

Design of a new probe for HSO₃⁻ ions.

Scheme 27

Detection of galactosidase enzyme with new ESIPT-based probe.

Scheme 28

Detection of amino acids with a benzothiazole core with ESIPT emission.

Scheme 29

Synthesis of imidazole-based probe 114 for detection of phosgene.

Scheme 30

ESIPT-based probe having benzothiazole and carborane rings for recognition of mustard gas.

Scheme 31

ESIPT-emitted imidazopyridine derivative.