Conformational aspects of the photochromic reactivity of two N-salicylidene aniline derivatives in a polymer matrix

Avădanei, Mihaela; Tigoianu, Radu; Serpa, Carlos; Pina, João; Cozan, Vasile

doi:10.1016/j.jphotochem.2016.09.024

Cited by 12 publications

(8 citation statements)

References 41 publications

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“…A detailed understanding of the effect of nonplanarity is essential to the rational control of ESIPT in nonplanar molecules or in sterically constrained environments where nonplanar rotamers may exist. Of the nonplanar molecules that exhibit ESIPT, the aromatic Schiff base salicylideneaniline (SA) and its derivatives have perhaps been the most thoroughly studied both experimentally and theoretically. − The ESIPT in SA is ultrafast and has been observed to complete within 50 fs of photoexcitation. ,, Following ESIPT, SA undergoes twisting about its phenolic bond; the excited-state lifetime of SA is controlled by this twisting motion and is fairly short. Recent estimates of the excited-state lifetime from time-resolved photoelectron spectroscopy (TRPES) are on the order of 1 ps in the gas phase .…”

Section: Introductionmentioning

confidence: 99%

Effect of Nonplanarity on Excited-State Proton Transfer and Internal Conversion in Salicylideneaniline

2018

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Salicylideneaniline (SA) is a prototype for excited-state intramolecular proton transfer (ESIPT) reactions in nonplanar molecules. It is generally understood that the dominant photochemical pathway in this molecule is ESIPT followed by nonradiative decay due to twisting about its phenolic bond. However, the presence of a secondary internal conversion pathway resulting from frustrated proton transfer remains a matter of contention. We perform a detailed nonadiabatic dynamics simulation of SA and definitively identify the existence of both reaction pathways, thereby showing the presence of a secondary photochemical pathway and providing insight into the nature of ESIPT dynamics in molecules with nonplanar ground-state geometries.

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Section: Introductionmentioning

confidence: 99%

Effect of Nonplanarity on Excited-State Proton Transfer and Internal Conversion in Salicylideneaniline

2018

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“…These spectral features have been assigned to the C=O stretching mode of the trans-keto tautomer of the SA molecule [7,10,55]. Very recently, the same attribution is suggested for a band at 1664 cm−1 observed in the IR spectra of SA derivatives in a polystyrene matrix upon irradiation [41]. Therefore, with a certain caution, the 1664 cm−1 peak in the spectra of M-ZSM-5 zeolites with large-size cations can be attributed to the presence of the trans-keto SA tautomer coexisting in the zeolite void with the other conformers.…”

Section: Discussionmentioning

confidence: 84%

“…For instance, Bogdan et al [ 34 ] obtained the displacement of the equilibrium between the phenolic tautomer and the quinoid one towards the keto form by adding ethanol into cyclohexane/ethanol mixture that increased the solvent’s polarity. To control photo-activity at the molecular level and to tune the effects of environment, salicylideneaniline and its derivatives were incorporated into specific nanoporous and mesoporous hosts, such as zeolites (typically faujasite) [ 23 , 24 , 35 , 36 , 37 ], mesoporous molecular silica (MCM-41 and SBA) [ 12 , 38 , 39 , 40 ], polymer matrix [ 41 ] and into micelles [ 12 ]. All these host structures provide an environment with a different degree of confinement and polarity and the life-time of transient species created upon photo-excitation after the encapsulation was found to depend on the pore size and the chemical composition of host.…”

Section: Introductionmentioning

confidence: 99%

A Spectroscopic Study of Tautomeric Equilibrium of Salicylideneaniline in ZSM-5 Zeolites

2019

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Salicylideneaniline (SA) sorbed in cation-exchanged M-ZSM-5 (M = H+, Li+, Na+, K+, Rb+, Cs+ and Zn2+) zeolites was studied by spectroscopic techniques assisted by quantum-chemical calculations. The nature of extra-framework cations present in the zeolite void was found to affect the spectral signature of the sorbed SA molecule that points to the shift of tautomeric equilibrium between the enol and keto forms. Small size cations, such as H+ and Li+, stabilize a cis-keto SA tautomer along with a enol one in the zeolite structure. The calculations indicate that the sorbed cis-keto tautomer may have the dipole large enough to be considered as a zwitterion. New features appearing in the spectra with the increase of the cation size were attributed to the presence of trans-keto SA tautomer, which up to now has been observed only in time-resolved spectroscopic experiments. A strong interaction of the molecule with cations in Zn-ZSM-5 zeolite results in the chelation of enol SA with the divalent Zn2+ ions. The results of the study suggest that the tautomeric equilibrium of molecules belonging to the Schiff base family can be tuned by the confinement in the nanoporous materials via a choice of topology of zeolite framework and the nature of extra-framework cations.

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“…Perceptible fluorescence decay is observed in the TCSPC experiment on salophen in PMMA (Figure B), unlike the case of salophen in solutions reported recently . The decay in PMMA multiexponential, similar to those of a salan derivative in a polymer matrix . They are faster than the decays from dropcast film and pure crystalline form of salophen.…”

Section: Results and Discussionmentioning

confidence: 99%

“…24 The decay in PMMA multiexponential, similar to those of a salan derivative in a polymer matrix. 36 They are faster than the decays from dropcast film and pure crystalline form of salophen. Thus, encapsulation in polymer matrix appears to bring in a sufficient degree of rigidification of salophen so as to make it a much stronger fluorophore than it is in solution but not quite as strong as in its crystalline form.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Impact of Molecular Arrangement and Torsional Motion on the Fluorescence of Salophen and Its Metal Complexes

Khan

Datta

2017

J. Phys. Chem. C

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Salophen is a weakly emissive molecule with a flexible structure. The decrease in the flexibility of the molecule, which can be achieved by chemical or physical means, causes a significant increase in the emissivity and fluorescence lifetime. This phenomenon has been observed upon incorporation of salophen in the solid polymer matrix of poly(methyl methacrylate) (PMMA). The enhancement in emission is even more prominent in the pure solid form of salophen. An enhancement of emission is also observed in the case of the zinc complex of salophen, SalZn, which is inherently more emissive than free salophen in solution. However, the enhancement in emission is greater in the PMMA matrix for the complex than in its solid form. Interestingly, a quenching of fluorescence is observed in the crystals of the aluminum complex of salophen (SalAl+), which is strongly emissive in solution phase. These apparently conflicting trends have been rationalized in the light of the molecular arrangement of salophen and its complexes in a solid matrix and in the pure solid forms. In the case of salophen, torsional motion provides major nonradiative channels of depopulation of its excited state in solution. These channels are blocked in the rigid environment provided of the polymer matrix and of the crystal, giving rise to aggregation induced enhancement of emission (AIEE). In the case of SalAl+, the torsional motion is restricted anyway due to complexation. The X-ray crystal structure indicates the possibility of π–π interaction between the planar ligands of two neighboring complex molecules, which could lead to aggregation-caused quenching (ACQ). This provides a justification for the lower emissivity of SalZn, as compared to SalAl+. SalZn is likely to exist as a dimer, in which intramolecular π–π interaction is possible. Thus, the emissivity of salophen and its complexes is found to be governed by interplay of torsional motion and intermolecular interaction. Experiments have been performed at liquid nitrogen temperature, whereby conformational motion is arrested, but additional intermolecular interactions are not brought in. Maximal fluorescence of each of the three species studied is observed in this condition.

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Conformational aspects of the photochromic reactivity of two N-salicylidene aniline derivatives in a polymer matrix

Cited by 12 publications

References 41 publications

Effect of Nonplanarity on Excited-State Proton Transfer and Internal Conversion in Salicylideneaniline

Effect of Nonplanarity on Excited-State Proton Transfer and Internal Conversion in Salicylideneaniline

A Spectroscopic Study of Tautomeric Equilibrium of Salicylideneaniline in ZSM-5 Zeolites

Impact of Molecular Arrangement and Torsional Motion on the Fluorescence of Salophen and Its Metal Complexes

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