Aggregation-induced emission of azines: An up-to-date review

ESIPT‐based AIE luminogens: Design strategies, applications, and mechanisms

“…Although more and more reviews on AIEgens and their applications have been published and discussions on ESIPT-based AIEgens have been included in some of them as a part, a comprehensive and systematic review on ESIPTbased AIEgens has not been presented. [146][147][148][149][150][151][152][153][154][155][156][157][158] In this review, we first summarize the commonly used ESIPT and AIE units and how to use them to construct ESIPT-based AIEgens, and then we discuss the applications of ESIPT-based AIEgens in different fields and the related sensing or working mech-…”

Mechanistic Insight into Selective Sensing of Hazardous Hg2+ and Explosive Picric Acid by Using a Pyrene‐Azine‐Hydroxyquinoline Framework in Differential Media

“…Firstly, structural feature of PHQ reveals large flexibility owing to multiple CÀ C, CÀ N and NÀ N single bonds resulting in active intramolecular rotations and rapid C=N isomerization reaction of azine functionality coupled with quinoline moiety as evident from some previous literature reports on some analogous azine based compounds. [33,34] Secondly, nitrogen lone pairs on hydroxyquinoline rings may be involved in strong intermolecular hydrogen bonding interaction with neighbouring water molecules in semi-aqueous medium that manifest in the formation of exciplex species between quinoline based excited state and a solvent molecule giving rise to weaker emission bands at higher wavelength region as also evident from some previous reports. [35,36] Thirdly, PET process involving lone pair of electrons on azine nitrogen atoms and photoexcited fluorophore moiety (as evident from theoretical studies to be discussed later, shown in Figure 10 and S11) also plays pivotal role in contributing weak emission of PHQ only.…”

Coherent Vibrational Spectrum via Time-Resolved Fluorescence for Molecular Dynamics and Identification of Emitting Species–Application to Excited-State Intramolecular Proton Transfer

“…ESIPT times of HBT and HBQ were determined to be 60 and 13 fs, respectively, and the NWPs of the product keto state have been reported by TA and TF. ,,, Salicylaldehyde azine (SAA) shown in Scheme is an aromatic Schiff base reported to undergo ESIPT and photochromic reactions. − One of the unique properties of SAA is that it is highly water-resistant because the primary enol form of SAA is highly energetically stabilized compared to others, whereas most aromatic Schiff bases are susceptible to hydrolysis . SAA also shows aggregation-induced emission, which, in conjunction with the ESIPT, has been exploited for fluorescence turn-on probe and cellular imaging. , It was reported that photoexcitation produces an excited cis-keto isomer, which returns to the ground state or undergoes twisting motion to form a trans-keto isomer. ,, The ESIPT time constants of salicylaldehyde (SA) and SAA were estimated to be faster than 50 fs (80 fs in ref ) by Ziolek et al, , whereas it was estimated to be 200–300 fs by Mitra and Tamai . SAA was suggested to undergo single proton transfer, although it has two equivalent channels of ESIPT, as shown in Scheme . , Molecules with two possible ESIPT sites that may allow excited-state intramolecular double proton transfer (ESIDPT) are interesting, but the mechanism of the double proton transfer, which can be concerted or stepwise, has been poorly investigated. − Determination of accurate reaction rate and recording of the NWPs of the product state(s), which could be the enol, mono-keto, and di-keto isomers, are essential to investigate the molecular dynamics of the ESIPT and ESIDPT.…”

“…24 SAA also shows aggregation-induced emission, which, in conjunction with the ESIPT, has been exploited for fluorescence turn-on probe and cellular imaging. 27,28 It was reported that photoexcitation produces an excited cis-keto isomer, which returns to the ground state or undergoes twisting motion to form a trans-keto isomer. 25,26,29 The ESIPT time constants of salicylaldehyde (SA) and SAA were estimated to be faster than 50 fs (80 fs in ref 29) by Ziolek et al, 26,29 whereas it was estimated to be 200−300 fs by Mitra and Tamai.…”