Evidence for competing proton-transfer and hydrogen-transfer reactions in the S1 state of indigo

Haggmark, Michael; Gate, Gregory; Boldissar, Samuel; Berenbeim, Jacob A.; Sobolewski, Andrzej L.; Vries, Mattanjah S. de

doi:10.1016/j.chemphys.2018.09.027

Cited by 14 publications

(15 citation statements)

References 28 publications

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“…The above proceeds efficiently if the molecule is excited to a state higher in energy than the energy barrier of the subsequent reaction process. 13,36 Table 2. The R2PI peak positions and vibrational frequencies in S1 of PBI-H2O and PBI-D2O are given in cm -1 along with the assignment.…”

Section: Structures Of Pbi-s Complexesmentioning

confidence: 99%

Excited State Deactivation via Solvent to Chromophore Proton Transfer in Isolated 1:1 Molecular Complex: Experimental Validation by Measuring the Energy Barrier and Kinetic Isotope Effect

Khodia¹,

Jarupula²,

Baweja³

et al. 2023

Preprint

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We have experimentally demonstrated conclusive evidence of solvent-to-chromophore excited state proton transfer (ESPT) as a deactivation mechanism in a binary complex isolated in the gas phase. The above was achieved by determining the energy barrier of the ESPT processes, qualitatively analysing the quantum tunnelling rates and evaluating the kinetic isotope effect. The 1:1 complexes of 2,2’-pyridylbenzimidazole (PBI) with H2O, D2O and NH3, produced in a supersonic jet-cooled molecular beam, were characterised spectroscopically. The vibrational frequencies of the complexes in the S1 electronic state were recorded using a resonant two-colour two-photon ionization method coupled to a Time-ofFlight mass spectrometer set-up. In the PBI-H2O, the ESPT energy barrier of 43110 cm-1 was measured using UV-UV hole-burning spectroscopy. The exact reaction pathway was experimentally determined by isotopic substitution of the tunnelling proton (in PBI-D2O) and increasing the width of the proton transfer barrier (in PBI-NH3). In both cases, the energy barrier was significantly increased to > 1030 cm-1 in the PBI-D2O and to > 868 cm-1 in PBI-NH3. The heavy atom in PBI-D2O decreased the zero-point energy in the S1 state significantly, resulting in the elevation of the energy barrier. Secondly, the solvent-to-chromophore proton tunnelling was found to decrease drastically upon deuterium substitution. In the PBI-NH3 complex, the solvent molecule formed a preferential hydrogen bonding with the acidic (PBI)N-H group. This led to the formation of a weak hydrogen bonding between the ammonia and the pyridyl-N atom, thus, increasing the proton transfer barrier width (H2NH‧‧‧Npyridyl(PBI)). The above resulted in increased barrier height and decreased quantum tunnelling rate in the excited state. The experimental investigation, aided by computational investigations, demonstrated conclusive evidence of a novel deactivation channel of an electronically excited biologically relevant system. The variation observed for the energy barrier and the quantum tunnelling rate by substituting NH3 in place of H2O can be directly correlated to the drastically different photochemical and photo-physical reactions of biomolecules under various microenvironments.

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Section: Structures Of Pbi-s Complexesmentioning

confidence: 99%

Excited State Deactivation via Solvent to Chromophore Proton Transfer in Isolated 1:1 Molecular Complex: Experimental Validation by Measuring the Energy Barrier and Kinetic Isotope Effect

Khodia¹,

Jarupula²,

Baweja³

et al. 2023

Preprint

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“…The fast non-radiative decay of indigo via hopping is the most accepted mechanism of photostability. This process explains why indigo is robustly photostable in the gas phase. ,,− …”

Section: Introductionmentioning

confidence: 98%

“…This process explains why indigo is robustly photostable in the gas phase. 16,19,[24][25][26][27][28][29][30][31][32][33][34][35]…”

mentioning

confidence: 99%

Surface Vacancy Generation by STM Tunneling Electrons in the Presence of Indigo Molecules on Cu(111)

et al. 2022

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Herein, we invesOgate the consequence of local voltage pulses on the adsorpOon state of single indigo molecules on the Cu(111) surface as well as on the atomic structure underneath the molecule. With a scanning tunneling microscope, at 5 K, intact molecules are imaged as two lobes corresponding to the electron density of each indoxyl moiety of the molecule which are connected by a carbon double bond. Then, two short successive voltage pulses with the Op placed above the molecule generate irreversible modificaOons, as revealed by consecuOve scanning tunneling microscopy (STM) imaging. Density-funcOonal theory calculaOons coupled to STM image calculaOons indicate the creaOon of a double surface vacancy of copper surface atoms below the oxygen atom of the indigo molecule as the most plausible scenario. These extracted copper atoms are stabilized as adatoms by the indigo oxygens, oxidizing each copper adatom to 0.32 electron. Introduc0onThe indigo molecule is an ancient organic dye molecule that has been used for centuries to dye colorful blue color texOles, and they even appear in recipes of Babylonian transcripts. 1 Nowadays, it is widely used as a pigment to dye billions of blue jeans per year. 2 On the other hand, due to the electronic, opOcal, and chemical properOes of the indigo molecule and its derivaOves, several applicaOons are explored such as field-effect transistors, 3,4 solar cells, 5,6 diodes, 7-9 memory storage devices, 10 diesel markers, 11 DNA biosensors, 12 or chemical detectors of NO 2 . 13 Also, the chemical structure of indigo moOvates exploring new chromophores with greater optoelectronic features. 14,15 There exist wide literature reports on indigo and its derivaOves with regard to the high photostability of the compounds. Three phenomena are invoked to account for an intramolecular change causing photostability: (1) photoexcitaOon of an excited state of the molecule for trans-cis isomerizaOon through the C═C bond; (2) isomeric change from the keto to monoenol configuraOon (Figure 1) by excited-state intramolecular proton (ESIP) transfer, where the hydrogen atom of the nitrogen atom is transferred to the oxygen; finally, (3) the isomeric dienol configuraOon resulOng from excited-state dual proton (ESDP) transfer, where both hydrogen atoms of the amine central groups are transferred to both oxygen atoms of the carbonyl groups. The first mechanism appears less favorable due to steric crowding between hydrogen atoms in the final form and the important interacOon of the hydrogen bonding between the carbonyl and N-H groups. [16][17][18][19][20] However, some thioindigo derivaOves show trans-cis isomerizaOon and the involvement of a triple state in the photoisomerizaOon 21,22 and parOcularly N,N′-di(tbutoxycarbonyl)indigo 23 shows the absence of intramolecular N-H•••O bonding. The photostability of indigo is thus been aiributed to the ESIP transfer from the keto to enol intramolecular isomerizaOon ajer irradiaOon (Figure 1), where the proton transfer occurs from the nitrogen to the oxygen atoms at th...

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“…Cis–trans isomerization around double bonds in conjugated compounds can be triggered by heat, light, or catalysts such as the addition of protons, transition metal ions, Lewis acids, and so on. Especially light-induced trans–cis photoisomerization of indigo and a variety of its derivatives has been widely studied. ,− As general conclusion from these studies, it was found that although many of the derivatives undergo double-bond isomerization in the excited state, indigo itself does not. The distinctive ingredients inhibiting photoisomerization in indigo have been suggested to be the NH···OC hydrogen bonds in the trans isomer, efficient excited-state proton transfer, and efficient nonradiative internal conversion quenching the photoisomerization channel. ,,, Indigo’s resistance to photoisomerization is key to its photostability as a pigment …”

Section: Introductionmentioning

confidence: 99%

“…The distinctive ingredients inhibiting photoisomerization in indigo have been suggested to be the NH••• OC hydrogen bonds in the trans isomer, efficient excitedstate proton transfer, and efficient nonradiative internal conversion quenching the photoisomerization channel. 5,6,9,11 Indigo's resistance to photoisomerization is key to its photostability as a pigment. 12 As an alternative to photoisomerization, protoisomerization of indigo, i.e., trans-to-cis isomerization induced by protonation, has also been addressed.…”

Section: ■ Introductionmentioning

confidence: 99%

Protoisomerization of Indigo and Isoindigo Dyes Confirmed by Gas-Phase Infrared Ion Spectroscopy

2019

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Gas-phase infrared multiple-photon dissociation (IRMPD) spectra are recorded for the protonated dye molecules indigo and isoindigo by using a quadrupole ion trap (QIT) mass spectrometer coupled to the free electron laser for infrared experiments (FELIX). From their fingerprint IR spectra (600—1800 cm–1) and comparison with quantum-chemical calculations at the density functional level of theory (B3LYP/6-31++G(d,p)), we derive their structures. We focus particularly on the question of whether trans-to-cis isomerization occurs upon protonation and transfer to the gas phase. The trans-configuration is energetically favored in the neutral forms of the dyes in solution and in the gas phase. Instead, the cis-isomer is lower in energy for the protonated forms of both species, but indigo is also notorious for not undergoing double-bond trans-to-cis isomerization, in contrast to many other conjugated systems. The IR spectra suggest that protoisomerization from trans to cis indeed occurs for both dyes. To estimate the extent of isomerization, on-resonance kinetics are measured on diagnostic and common vibrational frequencies to determine the ratio of cis-to-trans isomers. We find ratios of 65–70% cis and 30–35% trans for indigo versus 75–80% cis and 20–25% trans for isoindigo. Transition-state calculations for the isomerization reactions have been carried out, which indeed suggest a lower barrier for protonated isoindigo, qualitatively explaining the more efficient isomerization.

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Evidence for competing proton-transfer and hydrogen-transfer reactions in the S1 state of indigo

Cited by 14 publications

References 28 publications

Excited State Deactivation via Solvent to Chromophore Proton Transfer in Isolated 1:1 Molecular Complex: Experimental Validation by Measuring the Energy Barrier and Kinetic Isotope Effect

Excited State Deactivation via Solvent to Chromophore Proton Transfer in Isolated 1:1 Molecular Complex: Experimental Validation by Measuring the Energy Barrier and Kinetic Isotope Effect

Surface Vacancy Generation by STM Tunneling Electrons in the Presence of Indigo Molecules on Cu(111)

Protoisomerization of Indigo and Isoindigo Dyes Confirmed by Gas-Phase Infrared Ion Spectroscopy

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