Anuja Singh - Academia.edu (original) (raw)

Papers by Anuja Singh

Research paper thumbnail of Emergent cross-conjugated enediynyl fluorophores

O fluorophores with π-conjugated scaffolds are important because of their interesting optoelectro... more O fluorophores with π-conjugated scaffolds are important because of their interesting optoelectronic properties. In recent years, our lab has been engaged in understanding the photophysics of small diacetylene bridged fluorophores and found the diynes as a promising class of π-conjugated fluorophores. Building on these understandings, recently we have focused on the photophysics of a less explored class of cross-conjugated Y-shaped enediynes (one double and two triple bonds). Here, we present the photophysical properties of such enediynes which show interesting photophysical properties that include dual emissions from locally excited (LE) and intramolecular charge transfer (ICT) states and ring size dependent aggregate fluorescence in non-aqueous media. The dyes also show prominent aggregate fluorescence in mixed-aqueous solvents, and solid powder form. The enediynes with push-pull electronic substituents/moieties exhibit high contrast fluorescence color switching upon continuous ph...

Research paper thumbnail of Photophysics and peripheral ring size dependent aggregate emission of cross-conjugated enediynes: applications to white light emission and vapor sensing

Physical Chemistry Chemical Physics, 2018

Photophysical understanding of organic fluorophores with π-conjugated scaffolds is crucial as suc... more Photophysical understanding of organic fluorophores with π-conjugated scaffolds is crucial as such dyes are central to optoelectronic applications.

Research paper thumbnail of Photophysical Impact of Diacetylenic Conjugation on Classical Donor–Acceptor Electronic Energy Pair

The Journal of Physical Chemistry A, 2019

Organic fluorophores with extended π-conjugation are important for their widespread applications.... more Organic fluorophores with extended π-conjugation are important for their widespread applications. The present work provides photophysical insights of a diacetylene bridged classical donor-acceptor electronic energy pair, naphthalene-pyrene, in comparison with its part molecular structures, naphthyl and pyrenyl acetylenes as well as parent naphthalene and pyrene chromophores. The diacetylenic dye loses individual spectral identities of the donor and acceptor fluorophores exhibiting a locally excited (LE) emission (~411 nm) from the overall molecular entity with high fluorescence quantum yields (0.55-0.84) in non-aqueous media. In contrast to parent pyrene, the hybrid derivative shows strongly allowed S0→S1 transition. In mixed-aqueous media, the dye forms J-aggregates displaying a new red-shifted absorption (~425 nm) as well as emission (~510 nm) band. Unlike the hybrid dye, the naphthyl and pyrenyl acetylenes do not form aggregates. In the aggregate state of the hybrid fluorophore, electronic energy transfer takes place from the naphthyl moiety to pyrenyl ring. The excited state photophysical properties of the dye is exploited to vapor sensing in solid state.

Research paper thumbnail of Photophysics and Photoreactivity of Cross-Conjugated Enediynyl Aggregates: Applications to multi-parametric sensing of microheterogeneity and reversible fluorescence switching

Chemical Physics, 2019

Fluorescent aggregates find widespread applications in modern optoelectronics. Here, we study the... more Fluorescent aggregates find widespread applications in modern optoelectronics. Here, we study the photophysics of organic fluorophores composed of benzene, pyrene, naphthalene, and anthracene moieties connected via a Y-shaped enediyne π-spacer in water-acetonitrile solvent mixtures and solid forms. The fluorophores show a predominant aggregate emission band, which is ca. 4000 cm −1 red-shifted compared to their locally excited (LE) emission energies in water-acetonitrile. The aggregate emission is however blue-shifted compared to an intramolecular charge transfer (ICT) emission band. The interplay of the LE, ICT, and aggregate emissive states depends on peripheral aromatic units, electronic substituents and microenvironments. The LE to aggregate emission spectral shift is exploited to sensitively probe micro-heterogeneity in bile salts, which are complemented by fluorescence intensity and fluorescence anisotropy changes. The solution phase aggregate emissions closely resemble the solid state aggregate emission bands, which are attributed to excimer states. The aggregate fluorescence states in the solids are altered by external stimuli and reversibly switched multiple of cycles. The aggregates undergo photoreactions in mixed-aqueous solvents, but they remain unreactive in solid powder forms.

Research paper thumbnail of Resolving fluorescence signatures of a photoconvertible fluorophore by fluorescence spectroscopy and MCR-ALS-based combinatorial approach

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2021

Photoconvertible fluorophores are important for a myriad of applications in chemistry and biology... more Photoconvertible fluorophores are important for a myriad of applications in chemistry and biology. Here, we spectrally resolve and quantify individual photophysical information of a dual-emitting photoconvertible fluorophore by fluorescence spectroscopy and multivariate curve resolution-alternate least square techniques. We found that the reactant fluorophore, which shows a weak locally excited (LE) emission and a dominant intramolecular charge transfer (ICT) emission, also exhibits an intermolecular charge transfer emission. The ICT emission bands of both the reactant and product fluorophores are originated from their respective LE states. The reactant fluorophore is a mixture of its different ground state conformers. Higher yields of photoconversion of the yellow-emitting reactant fluorophore are achieved via a visible light photoreaction, leading to formation of pure white light at an intermediate photoreaction time. These findings together help us to glean new photophysical and photochemical insights into the photoreaction of a dual-emitting photoconvertible fluorophore.

Research paper thumbnail of Emergent cross-conjugated enediynyl fluorophores

O fluorophores with π-conjugated scaffolds are important because of their interesting optoelectro... more O fluorophores with π-conjugated scaffolds are important because of their interesting optoelectronic properties. In recent years, our lab has been engaged in understanding the photophysics of small diacetylene bridged fluorophores and found the diynes as a promising class of π-conjugated fluorophores. Building on these understandings, recently we have focused on the photophysics of a less explored class of cross-conjugated Y-shaped enediynes (one double and two triple bonds). Here, we present the photophysical properties of such enediynes which show interesting photophysical properties that include dual emissions from locally excited (LE) and intramolecular charge transfer (ICT) states and ring size dependent aggregate fluorescence in non-aqueous media. The dyes also show prominent aggregate fluorescence in mixed-aqueous solvents, and solid powder form. The enediynes with push-pull electronic substituents/moieties exhibit high contrast fluorescence color switching upon continuous ph...

Research paper thumbnail of Photophysics and peripheral ring size dependent aggregate emission of cross-conjugated enediynes: applications to white light emission and vapor sensing

Physical Chemistry Chemical Physics, 2018

Photophysical understanding of organic fluorophores with π-conjugated scaffolds is crucial as suc... more Photophysical understanding of organic fluorophores with π-conjugated scaffolds is crucial as such dyes are central to optoelectronic applications.

Research paper thumbnail of Photophysical Impact of Diacetylenic Conjugation on Classical Donor–Acceptor Electronic Energy Pair

The Journal of Physical Chemistry A, 2019

Organic fluorophores with extended π-conjugation are important for their widespread applications.... more Organic fluorophores with extended π-conjugation are important for their widespread applications. The present work provides photophysical insights of a diacetylene bridged classical donor-acceptor electronic energy pair, naphthalene-pyrene, in comparison with its part molecular structures, naphthyl and pyrenyl acetylenes as well as parent naphthalene and pyrene chromophores. The diacetylenic dye loses individual spectral identities of the donor and acceptor fluorophores exhibiting a locally excited (LE) emission (~411 nm) from the overall molecular entity with high fluorescence quantum yields (0.55-0.84) in non-aqueous media. In contrast to parent pyrene, the hybrid derivative shows strongly allowed S0→S1 transition. In mixed-aqueous media, the dye forms J-aggregates displaying a new red-shifted absorption (~425 nm) as well as emission (~510 nm) band. Unlike the hybrid dye, the naphthyl and pyrenyl acetylenes do not form aggregates. In the aggregate state of the hybrid fluorophore, electronic energy transfer takes place from the naphthyl moiety to pyrenyl ring. The excited state photophysical properties of the dye is exploited to vapor sensing in solid state.

Research paper thumbnail of Photophysics and Photoreactivity of Cross-Conjugated Enediynyl Aggregates: Applications to multi-parametric sensing of microheterogeneity and reversible fluorescence switching

Chemical Physics, 2019

Fluorescent aggregates find widespread applications in modern optoelectronics. Here, we study the... more Fluorescent aggregates find widespread applications in modern optoelectronics. Here, we study the photophysics of organic fluorophores composed of benzene, pyrene, naphthalene, and anthracene moieties connected via a Y-shaped enediyne π-spacer in water-acetonitrile solvent mixtures and solid forms. The fluorophores show a predominant aggregate emission band, which is ca. 4000 cm −1 red-shifted compared to their locally excited (LE) emission energies in water-acetonitrile. The aggregate emission is however blue-shifted compared to an intramolecular charge transfer (ICT) emission band. The interplay of the LE, ICT, and aggregate emissive states depends on peripheral aromatic units, electronic substituents and microenvironments. The LE to aggregate emission spectral shift is exploited to sensitively probe micro-heterogeneity in bile salts, which are complemented by fluorescence intensity and fluorescence anisotropy changes. The solution phase aggregate emissions closely resemble the solid state aggregate emission bands, which are attributed to excimer states. The aggregate fluorescence states in the solids are altered by external stimuli and reversibly switched multiple of cycles. The aggregates undergo photoreactions in mixed-aqueous solvents, but they remain unreactive in solid powder forms.

Research paper thumbnail of Resolving fluorescence signatures of a photoconvertible fluorophore by fluorescence spectroscopy and MCR-ALS-based combinatorial approach

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2021

Photoconvertible fluorophores are important for a myriad of applications in chemistry and biology... more Photoconvertible fluorophores are important for a myriad of applications in chemistry and biology. Here, we spectrally resolve and quantify individual photophysical information of a dual-emitting photoconvertible fluorophore by fluorescence spectroscopy and multivariate curve resolution-alternate least square techniques. We found that the reactant fluorophore, which shows a weak locally excited (LE) emission and a dominant intramolecular charge transfer (ICT) emission, also exhibits an intermolecular charge transfer emission. The ICT emission bands of both the reactant and product fluorophores are originated from their respective LE states. The reactant fluorophore is a mixture of its different ground state conformers. Higher yields of photoconversion of the yellow-emitting reactant fluorophore are achieved via a visible light photoreaction, leading to formation of pure white light at an intermediate photoreaction time. These findings together help us to glean new photophysical and photochemical insights into the photoreaction of a dual-emitting photoconvertible fluorophore.