ESIPT geometrical isomers with distinct mechanofluorochromism and intra/intermolecular H-bonding controlled tunable fluorescence

Abstract

Integrating intramolecular H-bonding functionality in organic fluorophore produces excited state intramolecular proton transfer (ESIPT) mechanism facilitated large Stokes shifted fluorescent materials. The tunable and environmental sensitive fluorescence of ESIPT molecules...

Dual emission of ESIPT-capable 2-(2-hydroxyphenyl)-4-(1H-pyrazol-1-yl)pyrimidines: interplay of fluorescence and phosphorescence

“…However, studies of isomeric ESIPT-capable molecules are relatively scarce in the literature. [89][90][91][92][93][94][95][96][97][98][99][100][101][102][103] Due to the presence of two nitrogen atoms in the positions 1 and 3 of the six-membered cycle, the pyrimidine ring offers particularly interesting opportunities for the synthesis of isomeric molecules. 104,105 For example, introducing the protondonating 2-hydroxyphenyl group in the positions 2 or 4(6) of the pyrimidine ring ensures the formation of a short O-HÁ Á ÁN intramolecular hydrogen bond as a pre-requisite for ESIPT and leads to two isomeric series of ESIPT-capable molecules (Scheme 2).…”

“…However, studies of isomeric ESIPT-capable molecules are relatively scarce in the literature. 89–103…”

Tuning the photophysical properties of ESIPT active unsymmetrical azine dyes by the change in the substituent and solvent: TD-PBE0 and TD-CAM-B3LYP studies

“…In another study, four organic fluorophores with two intramolecular H-bonding functionalities and unsymmetrical structures (salicylaldehyde–imine and benzophenone–imine) have been designed and explored. 38 All dyes showed tunable solid-state fluorescence between 536 and 645 nm dependent on inter/intramolecular H-bonding interaction. Four novel salicylaldehyde–diphenyl–azine (SDPA) skeleton-based luminogens with tunable emission have been synthesized by Jain et al 39 The photophysical studies in different solvents elucidated their ESIPT and AIE characteristics.…”

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

“…Azole and benzazole ESIPT-capable derivatives are workhorses in the area of ESIPT studies. − The most common molecular pattern of these compounds which is widely relied upon in the design of ESIPT dyes includes the proton-accepting azole/benzazole moiety combined with the proton-donating 2-hydroxyphenyl group or its analogues introduced in the α position to the azolic N atom. In contrast, pyrimidine derivatives are relatively rarely used for the design of ESIPT-fluorophores in comparison with azole and benzazole ones. ,− However, being combined with suitable proton-donating groups, they can serve as proton-accepting moieties. ,, Moreover, introducing additional donor groups in the pyrimidine core can lead to more complex molecular architectures of pyrimidine-based compounds suitable for binding metal ions and providing numerous sites for protonation, including isomeric ones. ,, In turn, the synthesis of isomeric ESIPT-capable compounds allows researchers to shed more light on the impact of structural factors on ESIPT and on relationships between ESIPT and luminescence. − The coordination of conventional dyes and ESIPT emitters to metal ions with d electronic configuration such as Zn 2+ is known to enhance the quantum efficiency of emission. − Earlier we demonstrated that emissions of 4-(1 H -pyrazol-1-yl)-6-(2-hydroxyphenyl)­pyrimidines and 2-(2-hydroxyphenyl)-4-(1 H -pyrazol-1-yl)­pyrimidines, which belong to two different isomeric families (Chart ), share such a common feature as dual emission associated with singlet-to-singlet and triplet-to-singlet transitions, which is contributed by anti-Kasha fluorescence of the tautomeric form. ,, However, their coordination behavior toward Zn 2+ ions appeared to be quite different, whereas the 4-(1 H -pyrazol-1-yl)-6-(2-hydroxyphenyl)­pyrimidine derivative can bind Zn 2+ ions through the N,N-site of the molecule, which produces multicolor emission of the complex, 2-(2-hydroxyphenyl)-4-(3,5-dimethyl-1 H -pyrazol-1-yl)­pyrimidine derivatives cannot do this. We associated this with steric effects imposed by methyl and phenyl substituents introduced in positions 3 and 5 of the pyrazolyl group.…”