Organic Near‐Infrared Luminescent Materials Based on Excited State Intramolecular Proton Transfer Process^†

Abstract

Organic near-infrared (NIR) luminescent materials have captured intense research interest owing to their potential applications in optical communication, data storage, bioimaging, sensing and night vision. Excited state intramolecular proton transfer (ESIPT) process with absorption in normal form while emission in tautomer form can lead to a distinct redshift emission, based on which, a lot of organic NIR luminescent materials were designed. Because of attractive features such as ultrahigh sensitivity to the surroundings, large Stokes shift, and inherent four level system, ESIPT based NIR luminescent materials are supposed to be ideal fluorescent probes and gain materials. In this review, first, organic near-infrared luminescent materials based on ESIPT process are summarized according to the core structures. Second, recent advances of ESIPT-based organic near-infrared fluorescent probes and organic NIR lasers are reviewed. Finally, the current challenges and prospects of ESIPT-based organic NIR luminescent materials are introduced.

Regulated stepwise ESDPT mechanism associated with chalcogen substitutions in BDIBD derivatives

“…Depending on photoexcitation, the acidity of proton donor groups is enhanced, leading to an increase in the basicity of acceptor groups. [21][22][23][24] Both these factors facilitate the generation of isomers through intramolecular or intermolecular PT reactions.…”

Substituent effect on photophysical properties and proton transfer process of HBQ derivatives

“…These characteristics make it potentially useful in many fields. For example, fluorescent probe [13][14][15][16][17], UV stabilizer [18,19], luminescent material [20][21][22], etc. In general, many factors can regulate ESIPT behavior, such as solvents, hydrogen bonding, and interactions with other molecules.…”

Complexes on the Base of a Proton Transfer Capable Pyrimidine Derivative: How Protonation and Deprotonation Switch Emission Mechanisms

“…Due to the large variety of emissive excited states, the emission of ESIPT-capable molecules is sensitive to various stimuli. − The breaking of the intramolecular hydrogen bond due to the interaction of the ESIPT site of the molecule with other molecules or ions or due to deprotonation causes strong changes in the luminescence response of ESIPT-capable molecules. The protonation of ESIPT-capable molecules can proceed at the hydrogen bond-accepting atom switching the ESIPT reaction off or at other heteroatoms leading to modulating ESIPT and ESIPT-coupled luminescence. − Binding metal ions by ESIPT dyes which is accompanied by the deprotonation in most cases (only rare examples of ESIPT-capable metal complexes are known) ,,− also results in strong changes of emission. − This sensitivity allows one to switch the emission of ESIPT-capable molecules between various emission mechanisms and makes them a multivariate platform for the design of stimuli-responsive emissive materials, probes, and sensors.…”