Tunable Twisting Motion of Organic Linkers via Concentration and Hydrogen-Bond Formation

El‐Zohry, Ahmed M.; Alturki, Abdullah; Yin, Jun; Mallick, Arijit; Shekhah, Osama; Eddaoudi, Mohamed; Ooi, Boon S.; Mohammed, Omar F.

doi:10.1021/acs.jpcc.9b00005

Cited by 18 publications

(34 citation statements)

References 54 publications

(155 reference statements)

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“…It is worth to mention that formations of molecular aggregates have been found to be responsible for many inconsistences in the reported optical absorption and emission values in the literature for coumarin dyes. [66][67][68][69] For example, if a coumarin dye is directly added to cyclohexane to prepare the solution (method A), or if the dye is first solubilized in very small amount of acetonitrile followed by diluted in cyclohexane (method B), the absorption values differ significantly due to formation of different extent of molecular aggregates. [68,69] Involvement of different charge transfer state of coumarin dyes in the excited state can be primarily unraveled through time resolved emission measurement.…”

Section: Solvatochromic Behavior Of Coumarin Dyesmentioning

confidence: 99%

An Insight of Molecular Twisting of Coumarin Dyes

Debnath

Ghosh

2020

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This article highlights the recent understanding of twisted intramolecular charge transfer state (TICT) of coumarin dyes on TiO 2 and Au NP surface. The natural origin of coumarin dye in several plants makes it attractive to solar cell and fluorescence sensing applications. Two different classes of D-π-A coumarin dyes, having cyano-acrylic acid as acceptor and 7-amino moiety as a donor, have been chosen: one of them, having 7-amino moiety in the ring, shows only intramolecular charge transfer (ICT) states in the excited state. While due to twisting of the free 7-amino moiety, the second class of coumarin shows both ICT and TICT states in their photo-excited states in the polar environment, in the form of a strong dual-fluorescence. On TiO 2 surface such coumarin dyes found to couple with carboxylic moiety, however on Au NP surface they bind with amino moiety. As a result, on TiO 2 surface, the 7-amino moiety is free to rotate, thus exhibiting TICT state which is a charge-separated state and leads to higher electron injection yield for the second class of coumarins. The applicability of such twisted conformers of coumarin molecules in the solar cell has been demonstrated. Furthermore, due to molecular coupling with the 7-amino moiety on Au NP surface, a restriction imposed on the molecular twisting of the free 7-amino group. This constrains the formation of the TICT state for the second class of coumarins on the Au NP surface. Such ICT-TICT fluorescence modulation character of the coumarin dyes may lead them to use for fluorescence sensing application, which is also demonstrated to detect specific ions and biomolecules. Thus the present review acmes very fundamental photophysical properties of coumarin dyes based on their molecular twisting on different solvents, semiconductors, and metal nanoparticles which have great consequences of real life applications.

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Section: Solvatochromic Behavior Of Coumarin Dyesmentioning

confidence: 99%

An Insight of Molecular Twisting of Coumarin Dyes

Debnath

Ghosh

2020

ChemistrySelect

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“… 12 Recently, it was shown that the TICT state stabilizes the charge separation in dye-sensitized solar cells (DSSCs) through small charge recombination rate. 4 , 13 − 16 For solar cell applications, a charge transfer process is designed to move from the donor to the acceptor moiety, forming an intramolecular charge transfer (ICT) state, 13 which is considered as a primary emissive state. Thus, the ICT state herein corresponds to the LE state in the traditional studied TICT molecules (see Figure 1 a).…”

Section: Introductionmentioning

confidence: 99%

Twisted Intramolecular Charge Transfer (TICT) Controlled by Dimerization: An Overlooked Piece of the TICT Puzzle

et al. 2021

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Organic dyes have shown high efficiencies in solar cells, which is mainly attributed to the push–pull strategy present in such dyes upon attaching to the semiconductor surfaces. We deeply studied the fundamental photophysical properties of cyanoacrylic dyes, mostly the L1 dye, and found unique emission properties that depend on many factors such as the solvent polarity and the concentration of the dye and could present a complete emission picture about this family of dyes. The L1 dye shows an intramolecular charge transfer (ICT) emission state at low concentrations (approximately nanomolar scale) and shows a twisted intramolecular charge transfer (TICT) emission state in specific solvents upon increasing the concentration to the micromolar scale. Moreover, the associated emission lifetimes of the ICT and TICT states of the L1 dye depend on solvent basicity, highlighting the role of hydrogen bond formation on controlling such states. Density functional theory calculations are performed to gain insight into the photophysical properties of the dye and revealed that H-bonding between the carboxylic groups triggers the dimerization at low concentrations. Using femtosecond transient absorption, we assigned the rate of TICT formation to be in the range (160–650 fs) −1 , depending on the size of the studied cyanoacrylic dye. Therefore, we add herein a new dimension for controlling the formation of the TICT state, in addition to the solvent polarity and acceptor strength parameters. These findings are not limited to the studied dyes, and we expect that numerous organic carboxylic acids dyes show similar properties.

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“…This high EQY of BR α crystals is possibly due to restriction of the ultrafast isomerization process of BR, which increase the barrier for the conical intersection in the excited state, as previously shown in similar systems. 10 − 12 , 29 , 30 Moreover, we interpret this red-emission peak as coming from M1, whose S 1 state is lower in energy with respect to M2 (492 vs 384 nm for M1 and M2, respectively). Then, we report transient-emission data measured on the BR β crystals in Figure 3 b.…”

Section: Resultsmentioning

confidence: 85%

“…To determine the amount of active nonradiative channels, the emission of BR crystals has been measured at low temperature (77 K), and, as it is apparent in Figure 4 a, the emission intensity increases by a factor of 3, meaning that the EQY can reach ∼75%. This indicates that nonradiative decay channels are still active at room temperature for the α crystal, suggesting a residual activity of large-scale motions, 20 , 29 , 30 , 39 − 42 aggregation effects, 21 , 29 , 43 or heat dissipation by crystal phonons. 44 , 45 …”

Section: Resultsmentioning

confidence: 99%

Highly Emissive Biological Bilirubin Molecules: Shedding New Light on the Phototherapy Scheme

et al. 2021

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Bilirubin (BR) is the main end-product of the hemoglobin catabolism. For decades, its photophysics has been mainly discussed in terms of ultrafast deactivation of the excited state in solution, where, indeed, BR shows a very low green emission quantum yield (EQY), 0.03%, resulting from an efficient nonradiative isomerization process. Herein, we present, for the first time, unique and exceptional photophysical properties of solid-state BR, which amend by changing the type of crystal, from a closely packed α crystal to an amorphous loosely packed β crystal. BR α crystals show a very bright red emission with an EQY of ca. 24%, whereas β crystals present, in addition, a low green EQY of ca. 0.5%. By combining density functional theory (DFT) calculations and time-resolved emission spectroscopy, we trace back this dual emission to the presence of two types of BR molecules in the crystal: a “stiff” monomer, M1, distorted by particularly strong internal H-bonds and a “floppy” monomer, M2, having a structure close to that of BR in solution. We assign the red strong emission of BR crystals to M1 present in both the α and β crystals, while the low green emission, only present in the amorphous (β) crystal, is interpreted as M2 emission. Efficient energy-transfer processes from M2 to M1 in the closely packed α crystal are invoked to explain the absence of the green component in its emission spectrum. Interestingly, these unique photophysical properties of BR remain in polar solvents such as water. Based on these unprecedented findings, we propose a new model for the phototherapy scheme of BR inside the human body and highlight the usefulness of BR as a strong biological fluorescent probe.

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Tunable Twisting Motion of Organic Linkers via Concentration and Hydrogen-Bond Formation

Cited by 18 publications

References 54 publications

An Insight of Molecular Twisting of Coumarin Dyes

An Insight of Molecular Twisting of Coumarin Dyes

Twisted Intramolecular Charge Transfer (TICT) Controlled by Dimerization: An Overlooked Piece of the TICT Puzzle

Highly Emissive Biological Bilirubin Molecules: Shedding New Light on the Phototherapy Scheme

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