Photophysical Insights Research Articles

Synthesis and photophysical insights of new fused N-heterocyclic derivatives with isoquinoline skeleton

Six new fused isoquinoline based compounds (compounds 5a–c with pyrrolo[2,1-a] isoquinoline structure and compounds 6a–c with imidazo[2,1-a]isoquinoline skeleton) have been synthesized using the [3 + 2] cycloaddition of the several in situ generated cycloimmonium ylides to ethyl propiolate or ethyl cyanoformate. All the synthesized compounds have been investigated in solution by UV–VIS absorption, steady and time-resolved fluorescence methods. The effect of the substituents on the spectral characteristics has been demonstrated. These derivatives displayed an intense emission between 360 and 420 nm. The emission quantum yields (Φ = 0.54–0.64) of pyrroloisoquinoline derivatives in dimethylsulfoxide (DMSO) were significantly higher than those of imidazoquinolines (0.03–0.16). The fluorescence decay of isoquinoline derivatives follows a biexponential law. A noticeable response of these isoquinoline derivatives to sodium hydroxide was observed.

Photophysical insights on a new supramolecular recognition element comprising PyC60 and a bisporphyrin studied in solution

The present work reports detailed photophysical insights on supramolecular interaction between C60 pyrrolidine tris-acid ethyl ester (PyC60) and a designed diporphyrin (1) in toluene. Both UV–vis and steady state fluorescence studies indicate effective complexation between PyC60 and 1 as revealed from the value of binding constant (K) of PyC60–1 complex, i.e., KPyC60–1 (UV–vis) = 7625 dm3·mol−1 and KPyC60–1 (fluorescence) = 9550 dm3·mol−1. Time-resolved fluorescence measurements evoke that the decay of photoexcited 1 in presence of PyC60 occurs only via static quenching mechanism and the magnitude of bimolecular quenching constant value for such system is enumerated to be 9.033 × 1011 dm3·mol−1·sec−1. In 1,2-dichlorobenzene (DCB), PyC60–1 system exhibits appreciable value of rate-constant of charge-separation (kcs) and quantum yield of charge-separation (ϕCS) than that observed in toluene. However, magnitude and order of both kcs (=5.35 × 107) and ϕCS (= 0.085) value for the PyC60–1 system estimated in DCB indicate that like toluene, there is no possibility of electron transfer in DCB. Both 1H and 13C NMR spectra of PyC60 molecule show appreciable shift of functional protons and carbon moiety of parent molecule in presence of 1, respectively. Quantum chemical calculations by ab initio method in vacuo establish the geometric structure of PyC60–1 complex and predict that dispersive forces associated with π-π interaction play significant role behind non-covalent interaction between PyC60 and 1.

Visualization of Charge Carrier Trapping in Silicon at the Atomic Surface Level Using Four-Dimensional Electron Imaging.

The ultrathin thickness (∼1-2 nm) of the native oxide layer on silicon surfaces, which acts as efficient trapping centers, precludes the possibility of studying its impact on the surface-charge carrier dynamics by conventional time-resolved laser spectroscopic techniques because of the large penetration depth of the pump and probe pulses. Here, we use four-dimensional scanning ultrafast electron microscopy (4D S-UEM) with unique surface sensitivity to directly visualize the charge carrier dynamics on Si(100) crystals before and after surface treatment (which removes the native oxide layer) in real space and time simultaneously. Our time-resolved snapshots of the top surface and Kelvin probe-force microscopy results demonstrate that the oxide layer can be formed within minutes after surface treatment, creating undesirable surface-trap states that destroy the population of photogenerated charge carriers on the surface and possibly at the device interface. This new surface observation provides critical photophysical insights into how a few atomic layers of oxide can dramatically influence charge carrier recombination dynamics in silicon solar cells.

Photophysical Impact of Diacetylenic Conjugation on Classical Donor-Acceptor Electronic Energy Pair.

Organic fluorophores with extended π-conjugation are important for their widespread applications. The present work provides photophysical insights into a diacetylene bridged classical donor-acceptor electronic energy pair, naphthalene-pyrene, in comparison with its constituents' molecular structures, naphthyl and pyrenyl acetylenes, as well as parent naphthalene and pyrene chromophores. The diacetylenic dye loses the 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 nonaqueous media. In contrast to the parent pyrene, the hybrid derivative shows a strongly allowed S0 → S1 transition. In mixed-aqueous media, the dye forms 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 are exploited in vapor sensing in the solid state.

Photophysical insights and in vitro cytotoxicity of dyes-gold nanostars system towards MCF-7 and A-549 cancer cells

In this paper, the interaction of phenothiazine (PHZ) dyes (Azure A (AZA) and thionine (TH)) with gold nanostars (Au NSs) were studied using absorption spectroscopy, steady state emission spectroscopy, high resolution transmission electron microscopy (HR-TEM), dynamic light scattering (DLS), Zetapotential measurements and Fourier transform infrared (FT-IR) spectroscopy. Absorption spectral studies of Au NSs in the presence of dyes resulted in a slight red shift on the surface plasmon resonance band (SPR) of Au NSs, suggesting the changes in the Au NSs surface owing to the adsorption of dyes. The phenomena of hypochromism and the appearance of coupled localized surface plasmon resonance (LSPR) bands in the absorption spectral studies of the AZA-Au NSs and TH–Au NSs systems suggested the vital role of electrostatic interactions between PHZ dyes and Au NSs. The formation of the ground state complex between dyes and Au NSs were evident from the outcome of the steady-state emission titration experiments of the dyes-Au NSs system. Further, the cytotoxic activity of AZA, TH, AZA-Au NSs and TH-Au NSs complexes on breast cancer (MCF-7) and A-549 cell lines were also investigated. These studies revealed that AZA-Au NSs, TH-Au NSs complexes showed the higher level of cytotoxicity than PHZ dyes treated cells.

Photophysical insights and guidelines for blue “turn‐on” fluorescent probes for the direct detection of nitric oxide (NO•) in biological systems

AbstractSynthesis and photophysical properties of a family of five blue fluorescent “turn‐on” probes for the direct detection of nitric oxide (NO•) is reported. The probes CB1‐5 feature a substituted 7‐hydroxy coumarin chromophore coupled to 2‐methyl‐8‐aminoquinoline, which act as tridentate ligand for Cu(II) and active site for monitoring NO• using a replacement strategy. The UV/vis absorption and fluorescence emission characteristics of the probes are significantly influenced by the substitution pattern on the coumarin ring, as well as by solvent polarity and pH. Time‐dependent density functional theory (TD‐DFT) calculations for CB4 and CB5 showed that the absorptions are due to π‐π* transitions localised on coumarin, with a small charge transfer contribution from the quinoline system at higher pH where the 7‐hydroxy coumarin moiety is deprotonated, which leads to a bathochromic shift of the absorption. Complexation of the probes with Cu(II) quenches the fluorescence, which is turned back on upon reaction with NO•, allowing selective detection of this important signalling molecule in μM concentrations. Preliminary experiments revealed that CB4 and CB5 enable to monitor endogenously produced NO• in living bacterial cells in multi‐dye imaging experiments.

Design and photophysical insights on graphene quantum dots for use as nanosensor in differentiating methamphetamine and morphine in solution.

Fluorescent graphene quantum dots (GQDs) were prepared and utilized as nanosensor for differentiation and determination of two most common narcotic drugs i.e. morphine and methamphetamine. The microstructure and optical properties of the GQDs were investigated by various physicochemical methods. XRD analysis indicated low crystalline nature, demonstrating the graphitic nature of the GQDs. According to the Tauc plot derived from UV-Vis spectrum, the optical band gap of the GQDs was determined to ~4.98 eV, assigned to the n-π* transitions. Cyclic voltammetry analysis of the GQDs determined electrochemical band gap of ~4.88 eV with HOMO and LUMO energies equal to -6.83 eV and -1.95 eV, respectively. The GQDs were employed as fluorescent sensing probe for determination of morphine and methamphetamine. The blue fluorescence of the prepared GQDs under the excitation at 362 nm was quenched in the presence of methamphetamine and enhanced in the presence of morphine. The detection limits of 1.48 and 0.5 μg/ml were found for methamphetamine and morphine, respectively. This inexpensive sensing system shows some advantages such as short response time (t < 1 min) and low detection limit as well as nontoxicity.

Photophysical insights on the influence of excited states reorganization processes on the visible and near infra-red luminescence of two-photon quadrupolar chromophores

We synthesized three different families of quadrupolar dyes, differing by the nature of their aromatic central cores (phenyl, fluorenyl, anthracenyl), in which we systematically varied the length of the π-conjugated backbone and the nature of the central bridge. We compared their linear and non-linear spectroscopic and photophysical features. We showed that the introduction of a diyne bridge is efficient in consistently increasing the Stokes shifts in these fluorophores, especially in high polarity solvents. By a combined theoretical and spectroscopic study we show that this feature is favoured by distortion of their π-conjugated skeleton at the electronic ground state. Unfortunately, this distortion process is generally detrimental to their fluorescence quantum yields. However, in the course of this study, we identify a particularly promising dye, that combines a large two-photon absorption (650 GM@760 nm) while keeping efficient emission (ϕf = 0.3) in the far-red/NIR (ca 700 nm) in polar solvent (DMSO).

Hybridizing Carbon Nitride Colloids with a Shell of Water-Soluble Conjugated Polymers for Tunable Full-Color Emission and Synergistic Cell Imaging.

We present the preparation of a new multicolor emission system constructed from two complementary conjugated materials that are highly photoluminescent, that is, phenyl-modified carbon nitride (PhCN) colloids as the core and water-soluble conjugated polymers (WSCPs) adsorbed as the shell. The fluorescence bands of the PhCN and WSCPs effectively complement each other and the overall emission can be simply adjusted to fully cover the visible light spectrum with white light emission also accessible. Photophysical insights imply that the interactions between PhCN and WSCPs preserve the binary system from emission distortion and degradation, which is essential to delicately tune the overall fluorescence bands. Notably, the continuously tunable emission color is achieved under single-wavelength excitation (365 nm). This hybrid shows a synergistic permeation performance in cell imaging, that is, PhCN nanoparticles help the WSCP to enter the cells and therefore multicolor cellular imaging achieved.

Photophysical insights behind zinc naphthalocyanine-gold nanoparticle interaction and its effect over supramolecular interaction between zinc napthalocyanine and PyC 60 in solution

Abstract This work envisages an efficient energy transfer phenomenon from zinc naphthalocyanine ( 1 ) to dodecanethiol functionalized gold nanoparticles (AuNp) having size of 3–6 nm in toluene. Significant enhancement in singlet energy transfer efficiency is observed for 1 -AuNp conjugate. Role of AuNp over the non-covalent interaction between 1 and C 60 pyrrolidine tris-acid ethyl ester (PyC 60 ) is studied by various spectroscopic tools; considerable reduction in the magnitude of binding constant for 1 -PyC 60 supramolecule is observed in presence of AuNp. Dynamic light scattering, atomic force microscope and scanning tunneling microscope measurements give clear evidence in favour of the surface binding of 1 to AuNp.

Spectroscopic insights on energy transfer phenomenon from phthalocyanine to gold nanoparticle and role of phthalocyanine-gold nanoparticle conjugate over supramolecular interaction between fullerene and phthalocyanine in solution

This letter envisages the photophysical insights on phthalocyanine (Pc)-gold nanoparticle (AuNp) conjugate in solution. Both steady state and time-resolved fluorescence studies evoke remarkable enhancement in energy transfer efficiency from ZnPc to AuNp in comparison to free-base Pc (H2Pc) in toluene. It is observed that in presence of AuNp, selectivity in binding for the non-covalent complex of H2Pc with PC70BM (a fullerene derivative) is found to be ∼3.0 times higher compared to ZnPc-PC70BM system. Dynamic light scattering, transmission electron microscope, atomic force microscope and fluorescence microscope measurements provide very good support in favour of the rationale behind Pc-AuNp interaction in solution.

New photophysical insights on effect of gold nanoparticles on the interaction between phthalocyanine and PC70BM in solution

Photoinduced processes in phthalocyanine/functionalized gold nanoparticles (Pc/AuNps) have been investigated by spectroscopic measurements. It is observed while AuNps reduce the magnitude of binding constant for the non-covalent complexation between [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) and H2-Pc by 15.8 times in comparison to PC70BM/ZnPc system in toluene, fluorescence of ZnPc is strongly quenched in presence of AuNp. Fluorescence lifetime determined by time-correlated single photon counting is also strongly reduced for ZnPc in presence of AuNp compared to H2-Pc. Symbolic enhancement in quantum yield of charge-separation associated with well-defined electrostatic interaction has been confirmed for PC70BM/ZnPc supramolecule in presence of AuNp. Transient absorption measurements establish that energy transfer mechanism is operative for both PC70BM/H2-Pc and PC70BM/ZnPc supramolecules in absence and presence of AuNp in toluene.

Photophysical insights into fullerene–porphyrazine supramolecular interactions in solution

This communication reports supramolecular interactions of a porphyrazine derivative, namely, 2,7,12,17-tetra-tert-butyl-5,10,15,20-tetraaza-21H,23H-porphine (1) with C60 and C70 in toluene and dichlorobenzene.

Absorption spectrophotometric, fluorescence and quantum chemical investigations on non-covalent interaction between PC70BM and designed diporphyrin in solution

Present work reports the photophysical insights on supramolecular interaction of a C70 derivative, namely, [6,6]-phenyl C71 butyric acid methyl ester (PC70BM), with two designed diporphyrin molecules having dithiophene (1) and carbazole (2) spacer in toluene and benzonitrile. Both absorption spectrophotometric and steady state fluorescence investigations reveal efficient complexation of PC70BM with 1 and 2 in both toluene and benzonitrile. The magnitude of average value of binding constant, viz., Kav, for the complexes of PC70BM with 1 and 2 in toluene (benzonitrile) are estimated to be 2.185×103dm3mol−1 (3.215×103dm3mol−1) and 10.180×103dm3mol−1 (25.405×103dm3mol−1), respectively. Selectivity in binding for the complexation process of PC70BM with 1 and 2 is estimated to be ∼4.6 and ∼7.90 as observed in toluene and benzonitrile, respectively. The complexation between PC70BM and diporphyrin is well accounted by a theoretical model which takes into account the electronic subsystems of both acceptor and donor. Ab initio calculations in vacuo establish that size selective orientation pattern of PC70BM towards the cavity of diporphyrin dictates the magnitude of binding and electronic structure of the PC70BM/diporphyrin complexes.

Photophysical insights on effect of gold nanoparticles over fullerene–porphyrin interaction in solution

The present article reports the role of gold nanoparticles, i.e., AuNp (having diameter ∼2–4nm), in non-covalent interaction between fullerenes (C60 and C70) and a monoporphyrin (1) in toluene. Both UV–vis and fluorescence measurements reveal considerable reduction in the average value of binding constant (Kav) for the C70–1 system (KC70–1(av)=19,300dm3mol−1) in presence of AuNp, i.e., KC70–1–AuNp(av)=13,515dm3mol−1 although no such phenomenon is observed in case of C60–1 system, viz., KC60–1(av)=1445dm3mol−1 and KC60–1–AuNp(av)=1210dm3mol−1. DLS study reveals sizeable amount of increase in the particle size of C70–1–AuNp nanocomposite, i.e., ∼105nm, compared to C60–1–AgNp system, e.g., ∼5.5nm which gives very good support in favor of decrease in the value of Kav for the former system. SEM study reveals that nanoparticles are dispersed in larger extent in case of C70–1–AuNp system. Time-resolved fluorescence study envisages that deactivation of the excited singlet state of 1 by C70 takes place at a faster rate in comparison to C60 in presence of gold nanoparticles.

Role of charge transfer interaction and the chemical physics behind effective fulleropyrrolidine/porphyrin non-covalent interaction in solution

The present paper reports the photophysical insights on supramolecular interaction of a monoporphyrin derivative, namely, 1, with C60 pyrrolidine tris-acid ethyl ester (PyC60) in toluene and benzonitrile. The ground state interaction between PyC60 and 1 is facilitated through charge transfer interaction. Both UV–Vis and steady state measurements elicit almost similar magnitude of binding constant for the PyC60/1 complex in toluene and benzonitrile, viz., 6825 and 6540dm3mol−1, respectively. Life time measurement evokes that rate of charge separation is fast in benzonitrile. Both hybrid-DFT and DFT calculations provide very good support in favor of electronic charge-separation in PyC60/1 system in vacuo.

Spectroscopic and theoretical insights on effective and selective non-covalent binding between fullerenes (C60 and C70) and a designed diporphyrin in solution

The present work reports the photophysical insights behind effective non-covalent interaction between a designed diporphyrin (1) and fullerenes C60 and C70 in toluene. Ground state electronic interaction between fullerenes and 1 is evidenced from UV–Vis measurements in which it is observed that the intensity of the Soret absorption band of 1 is decreased considerably in presence of both C60 and C70. Steady state fluorescence studies reveal efficient quenching of the fluorescence intensity of 1 in presence of fullerenes. Evaluation of binding constants for the fullerene/1 systems evoke that 1 may be employed as an efficient molecular tweezers for C70 in toluene as selectivity in binding is determined to be ∼9.4. Time resolved emission studies establish relatively long-lived charge separated state for the C70/1 system in comparison to C60/1. Molecular mechanics calculations by force field method in vacuo interpret well regarding stability difference between C60 and C70 complexes of 1 and give formidable support in favor of side-on orientation motif of C70 towards the plane of 1 during non-covalent complexation process.

Spectral signature of a Ru(ii, iii, iv) complex: a combined experimental and theoretical investigation

The electronic and geometrical features of a recently synthesized ruthenium β-diketonato complex with a protected ethynyl ligand ([Ru(dbm)2(acac-TIPSA)], dbm = dibenzoylmethanate ion, acac-TIPSA = 3-(triisopropylsilyl)acetylene-2,4-pentanedionate ion), a building block for molecular spintronic devices, were analyzed as a function of its oxidation degree using Density Functional Theory (DFT) and Time Dependent DFT (TD-DFT), for ground and excited state properties, respectively, and compared to the available experimental data. The UV-Vis spectral signature of a native Ru(III) neutral form computed at a TD-DFT level was compared to those of the oxidized Ru(IV) and reduced Ru(II) ones, allowing us to clearly identify the nature of all bands occurring in this spectral region and thus providing important photophysical insights for the use of this complex as a building block in polynuclear organometallic mixed valence molecular systems able to perform a swapping operation under light control.

CNTs in Optoelectronic Devices: New Structural and Photophysical Insights on Porphyrin‐DWCNTs Hybrid Materials

AbstractThe preparation and physical characterization of diverse porphyrin‐derived double‐walled carbon nanotubes (DWCNTs) conjugates are described. A porphyrin molecule is covalently linked and physically adsorbed to COOH‐derived DWCNTs. The photophysical properties of all porphyrin‐CNTs derivatives are studied in solution and in polymeric matrices. Definitive experimental evidence for photoinduced electron and/or energy transfer processes involving the porphyrin chromophores and the CNT wall is not obtained, but solid‐state UV‐vis absorption profiles display electronic transitions fingerprinting J‐ and H‐ type aggregates, where porphyrin molecules intermolecularly interact “head‐to‐tail” and “face‐to‐face”, respectively. In parallel, molecular modeling based on force‐field simulations is performed to understand the structure of the porphyrin‐CNTs interface and the nature of the interactions between the porphyrins and the DWCNTs. Finally, multilayered‐type devices are fabricated with the aim of investigating the interaction of the porphyrin‐derived DWCNTs with poly(3‐hexylthiophene)‐pyrene matrices containing small amounts of 1‐[3‐(methoxycarbonyl)propyl]‐1‐phenyl‐[6.6]C61.

New Photophysical Insights in Noncovalent Interaction between Fulleropyrrolidine and a Series of Zincphthalocyanines

The present article reports, for the first time, the photophysical aspects of noncovalent interaction of a fullerene derivative, namely, C(60) pyrrolidine tris-acid ethyl ester (PyC(60)) with a series of zincphthalocyanines, for example, underivatized zincphthalocyanine (1), zinc-1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (2), and zinc-2,3,9,10,16,17,23,24-octakis-(octyloxy)-29H,31H-phthalocyanine (3) in toluene. Ground state electronic interaction of PyC(60) with 1, 2 and 3 has been evidenced from the observation of well-defined charge transfer (CT) absorption bands in the visible region. Utilizing the CT transition energy, vertical electron affinity (E(A)(v)) of PyC(60) is determined. Steady state fluorescence experiment enables us to determine the value of binding constant (K) in the magnitude of 2.60 × 10(4) dm(3)·mol(-1), 2.20 × 10(4) dm(3)·mol(-1), and 1.27 × 10(4) dm(3)·mol(-1) for the noncovalent complexes of PyC(60) with 1, 2, and 3, respectively. K values of PyC(60)-ZnPc complexes suggest that PyC(60) is incapable of discriminating between 1, 2, and 3 in solution. Lifetime experiment signifies the importance of static quenching phenomenon for our presently investigated supramolecules and it yields larger magnitude of charge separated rate constant for the PyC(60)-1 species in toluene. Photoinduced energy transfer between PyC(60) and ZnPc derivatives, namely, 1, 2, and 3, in toluene, has been evidenced with nanosecond laser photolysis method by observing the transient absorption bands in the visible region; transient absorption studies establish that energy transfer from (T)PyC(60)* to the ZnPc occurs predominantly, as confirmed by the consecutive appearance of the triplet states of PyC(60). Theoretical calculations at semiempirical level (PM3) evoke the single projection geometric structures for the PyC(60)-ZnPc systems in vacuo, which also proves that interaction between PyC(60) and ZnPc is governed by the electrostatic mechanism rather than dispersive forces associated with π-π interaction.