One-photon Excitation Research Articles

Properties and Synthetic Performances of Phenylamino Cyanoarenes under One-Photon Excitation Manifolds

AbstractThe synthesis of a set of new organic photocatalysts (PCs) with a donor-acceptor carbazolyl dicyanobenzene structure is reported. The PCs developed have fine-tailored redox potentials from –1.62 V (PC•+/PC*) to 1.36 V (PC*/PC•–) and were accessed through a straightforward two-step synthesis. The potential of these PCs was demonstrated in synthetically relevant reactions with mechanistically opposite thermodynamic requirements, previously reported only in the presence of precious Ir-based PCs. In addition, the PCs outperformed the yields promoted by the well-established 4CzIPN organic dye in both type of reactions.

The Raman and hyper-Raman scatterings of light by LO-phonons in a CdS crystal under excitation near resonance with the An=2and Bn=1exciton levels

AbstractThe theoretical treatment of the scattering of light by LO-phonons under one-photon and two-photon excitation near resonance with the An=2and Bn=1exciton levels in a CdS crystal is given. The influence of the complex structure of the top valence band on these levels is taken into account by the use of the perturbation theory. Assumption of the nonzero matrix elements of the dipole transitions between the A and B sub-bands leads to the fact that the linear combinations of the 1s and 2p exciton wave functions conform to the two “perturbed” energy levels. The possible manifestations of this mixing of states in the resonance Raman and hyper-Raman scatterings are considered.

Construction of a unique two-photon fluorescent probe and the application for endogenous CO detection in live organisms.

Carbon monoxide (CO) is one of the most significant signal molecules and plays an important role in regulating human physiological and pathological processes. In this study, a novel Pd-based complex (Pd-BNP-OH) was developed for endogenous CO detection. The structure and morphology of Pd-BNP-OH was characterized by SEM, XPS, and NMR analyses. When Pd-BNP-OH was reacted with CO, a strong fluorescence enhancement at 510nm was observed. In addition, Pd-BNP-OH exhibited high stability and selectivity toward CO in PBS buffer. In biological experiments, Pd-BNP-OH exhibited little cytotoxicity in cellular environment, and a bright fluorescence turn on was observed in the presence of exogenous CO and endogenous generated CO. The probe was then applied for CO detection in live zebrafish by both one-photon and two-photon excitation. Significantly, Pd-BNP-OH has excellent two-photon property, controllable structure and high biocompatibility. These features enable the probe to detect endogenously generated carbon monoxide in live organisms successfully.

Effects of linkage between donors on photoinduced charge transfer in one-photon and two-photon absorption of Donor-π-Donor-π-Acceptor conjugates

Photoinduced charge transfer (CT) mechanisms of two Donor-π-Donor-π-Acceptor conjugates composed of ferrocene (Fc), zinc-porphyrin (ZnP), and fullerene (C60) linked by phenylene–acetylene/acetylene during the one- (OPA) and the two-photon absorption (TPA) processes are analyzed theoretically based on the density functional theory calculations and visualization methods to study the effects of linkage between the two donors on the excitation characteristics. The change of bridge affects the efficiency of superexchange CT from Fc to ZnP in the OPA process. The one-photon excitations are dominated by local transitions of ZnP and Fc, and there is almost no efficient CT from the donors to the acceptor for both the two researched structures. In contrast, the advantage of superexchange CT from ZnP to C60 becomes much larger than the other transition forms during the TPA process when the linkage between ZnP and Fc is changed from acetylene to phenylene–acetylene. This linkage effect in TPA would have great significance in designing novel optoelectronic devices.

Carbazole-functionalized dipicolinato LnIII complexes show two-photon excitation and viscosity-sensitive metal-centered emission

EuIII and YbIII complexes with the carbazole-dipicolinato ligand dpaCbz2−, namely K3[Eu(dpaCbz)3] and K3[Yb(dpaCbz)3], were isolated. The EuIII complex displayed metal-centered emission upon one-photon excitation with a sensitized emission efficiency ΦLLn of 1.8±0.3%, corresponding to an intrinsic emission efficiency ΦLnLn of 46% and a sensitization efficiency of ηsens 3.9%, with an emission lifetime of the emissive state τ of 1.087±0.005 ms. The YbIII complex displayed ΦLLn of 0.010±0.001%, and a τ of 2.32±0.06 μs The EuIII-centered emission was sensitized as well upon two-photon excitation and a two-photon absorption cross-section σ2PA of 63 GM at 750 nm was determined for the complex. The one- or two-photon sensitized emission intensity of the EuIII complex changes by more than two-fold when the solvent viscosity is varied in the range 0.5–200 cP and the emission is independent of dissolved oxygen. The YbIII complex displays a change in emission intensity as well. However, in this case, a dependence of the emission intensity on dissolved oxygen content was observed.

Linear Optical Absorptions of Photo/Thermochromic Organic Molecules Interacting with a Gold Nanoparticle

We present linear optical absorptions of photo/thermochromic molecules interacting with a gold nanoparticle. The photo/thermochromic system is the dihydroazulene/vinylheptafulvene (DHA/VHF) system and our aim is to study the effects of the interaction between the gold nanoparticle and the molecular systems. We consider the changes of the one-photon excitations of the dihydroazulene/vinylheptafulvene system as we increase the interactions between the molecules and the nanoparticle by decreasing the distance between them. We utilize a quantum mechanical/molecular mechanical method for investigating the photo/thermochromic molecular system interacting with the gold nanoparticle. The photo/thermochromic molecules are described quantum mechanically using density functional theory whereas the gold nanoparticle is represented as gold atoms with atomic polarizabillities using molecular mechanics.
 We observed that the optical properties of the photo/thermochromic systems are affected by the presence of the nanoparticle and the changes depend strongly on the conformer of the molecular system along with the relative orientation and distance between the photo/thermochromic molecules and the nanoparticle.

Coincidence ion pair production (cipp) spectroscopy of diiodine.

Coincidence ion pair production (I+ + I-) (cipp) spectra of I2 were recorded in a double imaging coincidence experiment in the one-photon excitation region of 71 600-74 000 cm-1. The I+ + I- coincidence signal shows vibrational band head structure corresponding to iodine molecule Rydberg states crossing over to ion-pair (I+I-) potential curves above the dissociation limit. The band origin (ν0), vibrational wavenumber (ωe) and anharmonicity constants (ωexe) were determined for the identified Rydberg states. The analysis revealed a number of previously unidentified states and a reassignment of others following a discrepancy in previous assignments. Since the ion pair production threshold is well established, the electric field-dependent spectral intensities were used to derive the cutoff energy in the transitions to the rotational levels of the 7pσ(1/2) (v' = 3) state.

Imaging photodissociation dynamics of MgO at 193 nm

In this work, we used time-sliced ion velocity imaging to study the photodissociation dynamics of MgO at 193 nm. Three dissociation pathways are found through the speed and angular distributions of magnesium. One pathway is the one-photon excitation of MgO(X1Σ+) to MgO(G1Π) followed by spin-orbit coupling between the G1Π, 33Π and 15Π states, and finally dissociated to the Mg(3Pu)+O(3Pg) along the 15Π surface. The other two pathways are one-photon absorption of MgO(A1Π) state to MgO(G1Π) and MgO(41Π) state to dissociate into Mg(3Pu)+O(3Pg) and Mg(1Sg)+O(1Sg), respectively. The anisotropy parameters of the dissociation pathways are related to the lifetime of the vibrational energy levels and the coupling of rotational and vibronic spin-orbit states. The total kinetic energy analysis gives D0(Mg−O)=21645±50 cm−1.

Optical gain appearance in the CdSe/CdS nanoplatelets colloidal solution

The experimental investigations of the colloidal heterostructured CdSe/CdS nanoplatelets transient absorption in the regime of one-photon stationary excitation of excitons by high-intensity nanosecond laser pulses are presented. A strong dependence of exciton’s transitions behavior on nanoplatelets concentration in colloidal solution and pump intensities was studied for the first time. The revealed nonlinear transmission changes of the nanoplatelets solutions with different optical density were explained by the presence of phase space filling effect, energy exchange between exciton states, reabsorption processes and exciton–exciton interaction. The most vital result of the paper is the identification of conditions for the existence of the optical gain in colloidal solutions of nanoplatelets.

Strengthened near-IR two-photon absorption induced emission of ESIPT chromophores by molecular aggregation

In this study, a range of new free open-chain conjugated organic chromophores including salicylidene methylamine part were synthesized and characterized. The steady state and transient state absorption and emission properties of the target dyes in DMF were investigated. The results showed that the target dyes processed the excited state intramolecular proton transfer (ESIPT) in DMF under one-photon excitation. Furthermore, the ESIPT was more competitive under the exposure of pulsed pumping near-IR femotosecond laser in DMF. The further survey showed that the target dyes yielded gradually the regular molecular aggregates in the mixed DMF/H 2 O (the water volume fractions, 60–80%) with evolving time. In particular, the target molecular aggregates exhibited the strong enol emission but the quenched keto emission under one-photon exposure and near-IR two-photon irradiation, respectively. In addition, the near-IR two-photon absorption (TPA) induced enol emission of the target dyes showed an enhancement in the aggregation state. This study demonstrates that it is feasible to strengthen TPA induced emission of enol phototautomers of some ESIPT compounds by the molecular aggregation under the irradiation of near-IR femotosecond laser. Strengthened near-IR two-photon absorption induced emission of a variety of ESIPT chromophores by molecular aggregation in mixed organic solvents/H 2 O

Dependence of the nonlinear optical response of CdSe nanoscrolls on coating with oleic or acetic acid

The photoluminescence and nonlinear transmission of atomically thin population of colloidal CdSe rolled-up nanosheets were investigated at the one-photon stationary excitations of excitons by the third harmonic of Nd3+:YAP laser pulses. It was revealed that the nonlinear optical response of the nanoscrolls is strongly influenced by multiwalled rolled-up structure. The broadening of exciton band and the red shift of the photoluminescence were observed and explained by coupling effect within the folded scroll-layers.

Low-Threshold Amplified Spontaneous Emission from Air-Stable CsPbBr3 Perovskite Films Containing Trace Amounts of Polyethylene Oxide.

Organic additives can enhance the amplified spontaneous emission (ASE) performance of inorganic cesium lead halide perovskites (CsPbBr3 ) but volatility, potential hygroscopicity and oxidative degradation of these additives jeopardizes the thermal stability and shelf-life of blended CsPbBr3 films. To address this problem, we have fabricated perovskite films in a two-step solution protocol involving as little added polyethylene oxide (PEO) as possible. These films exhibited enhanced crystallization, improved photoluminescence (PL) intensity and prolonged lifetimes. Their hierarchical morphology and surface passivation lowered the ASE threshold from 278 to 176 μЈ/cm2 under one-photon nanosecond laser excitation. The proportion of added PEO was 0.3 wt% and was subsequently almost fully removed, thereby reducing its adverse influence on the stability of resulting films under continuous pulsed laser excitation. Stable ASE spectra could be stimulated after storage in air for 10 months.

Prospects for More Efficient Multi-Photon Absorption Photosensitizers Exhibiting Both Reactive Oxygen Species Generation and Luminescence.

The use of two-photon absorption (TPA) for such applications as microscopy, imaging, and photodynamic therapy (PDT) offers several advantages over the usual one-photon excitation. This creates a need for photosensitizers that exhibit both strong two-photon absorption and the highly efficient generation of reactive oxygen species (ROS), as well as, ideally, bright luminescence. This review focuses on different strategies utilized to improve the TPA properties of various multi-photon absorbing species that have the required photophysical properties. Along with well-known families of photosensitizers, including porphyrins, we also describe other promising organic and organometallic structures and more complex systems involving organic and inorganic nanoparticles. We concentrate on the published studies that provide two-photon absorption cross-section values and the singlet oxygen (or other ROS) and luminescence quantum yields, which are crucial for potential use within PDT and diagnostics. We hope that this review will aid in the design and modification of novel TPA photosensitizers, which can help in exploiting the features of nonlinear absorption processes.

Fluorescein isothiocyanate-doped conjugated polymer nanoparticles for two-photon ratiometric fluorescent imaging of intracellular pH fluctuations

Herein, we report a two-photon ratiometric fluorescent pH nanosensor based on conjugated polymer poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) nanoparticles loaded with pH-sensitive fluorescein isothiocyanate (FITC) for intracellular pH monitoring. The obtained nanosensor (FITC-PFO NPs) possesses high sensitivity, excellent stability, good reversibility, favorable two-photon excitability and low cytotoxicity. The ratiometric fluorescence of FITC and PFO (F517/F417) in FITC-PFO NPs solution shows an efficient pH-sensitive response over the pH range from 3 to 10 (pKa = 6.43) under two-photon excitation. Additionally, the FITC-PFO NPs is successfully applied for ratiometric imaging of intracellular pH and its fluctuation in both one-photon and two-photon excitation modes. Overall, the two-photon pH nanosensor based on FITC-PFO NPs exhibits great potential in crucial physiological and biological processes related to intracellular pH fluctuations.

Laser ionisation detection of O(3 P j ) atoms in the VUV; application to photodissociation of O2

Detection of O() atoms using one-photon resonant excitation to the state at nm followed by near-threshold ionisation, i.e. 1 + 1' resonance-enhanced multi-photon ionisation, has been investigated. The aim was to achieve low ion recoil, improved sensitivity, and reliable angular momentum polarisation information, with an as simple as possible laser setup. An efficient 1 + 1' scheme has been found where the VUV light for the first step is generated by difference frequency () VUV generation, and the ionisation step 1' uses around 289 nm. The presented scheme induces 9 m/s recoil of the O ion using a two-dye laser system, and zero recoil should be possible by generating 302 nm radiation with a third dye laser. While this approach is much more sensitive than a previous 1 + 1' scheme using 212.6 nm for the 1' step, we found that the relatively intense radiation of the beam does not saturate the 1' step. To test the ability of this scheme to accurately determine branching ratios, fine structure yields, and angular distributions including polarisation information, it has been applied to O photodissociation around 130 nm with subsequent O() fragment detection.

Near-IR two-photon absorption photostabilizers for polymers intensified by molecular assembly in mixed organic solvents/H2O

This study reported on a variety of target phenanthridine dyes carrying hydroxy groups that were employed as near-IR two-photon absorption (TPA) photostabilizers for polymers. It was demonstrated that the target phenanthridine dyes underwent reversible excited state proton transfer (ESPT) in strong polar protic and aprotic solvents, such as ethanol, which was more remarkable under near-IR two-photon excitation. It was determined that the target dyes processed regular molecular stacking in mixed organic solvents/H2O solvents (such as ethanol/H2O, 90% water volume). The orderly molecular aggregation of the target phenanthridine dyes intensified the reversible ESPT emission under one-photon and near-IR two-photon excitation, respectively. Hence, the absorbed energy was consumed by the reversible ESPT process of the target dyes. As a consequence, the target dyes were evaluated as near-IR TPA photostabilizers for polymers. In contrast, the reference phenanthridine dyes lacking of hydroxy groups did not exhibit ESPT or photostability under light irradiation.

Investigation of the luminescence properties of ZnO clusters induced by single-photon and two-photon excitation

By using a luminescence spectrometer and femtosecond laser, we have investigated the specific optical properties and excitation mechanism of ZnO clusters with one-photon and two-photon excitations. When the excitation wavelength was chosen to be 360 nm, the strongest luminescence intensity was observed. However, the luminescence intensity decreased gradually and the emission peak was red shifted slowly with increasing excitation wavelength (from 360 to 400 nm). When the excitation wavelength was chosen to be 780 nm, the luminescence intensity increased nonlinearly with increasing excitation intensity. What is even more interesting is that ZnO clusters could be used in the imaging of living cells under two-photon excitation, implying the potential applications for the optical properties of ZnO clusters in the field of biophotonics.

Auger Dynamics in InP/ZnSe/ZnS Quantum Dots Having Pure and Doped Shells

In this study, we report the negative trion and biexciton Auger dynamics in very high-quality InP/ZnSe/ZnS quantum dots (QDs) having varying amounts of indium-based traps in the ZnSe shell. Negative trion times are determined by time-correlated photon-counting measurements on QDs that have been photoreduced with lithium triethylborohydride. We find that the Auger times vary from 280 to 425 ps and scale linearly with the total particle volume. Excess indium in the ZnSe shell gives rise to hole traps that are transiently populated following photoexcitation. Comparing stoichiometric and nonstoichiometric particles, we find that the negative trion lifetimes are independent of the presence of indium in the ZnSe shell. Biexciton dynamics are determined from transient absorption (TA) bleach recovery measurements. Absorption of two photons results in the formation of two types of biexcitons: those having both holes in the InP core (XX state) and those having one hole trapped in the ZnSe shell (XT state). XX state Auger times are measured in stoichiometric QDs, and for these particles, the Auger times are ∼80 ps. Nonstoichiometric QDs show an additional long TA decay component, assigned to Auger recombination of the XT state. A previous study (J. Phys. Chem. C2021, 125, 4110–4118) found that hole trapping at indium-based shell traps results in a slow photoluminescence (PL) rise component. We find that the fraction of the XT state formed by the absorption of two photon correlates with the product of the fraction of slow PL rise and the rise time constant following one-photon excitation.

Ultrafast carrier dynamics of Cu2O thin film induced by two-photon excitation* *Project supported by the National Natural Science Foundation of China (Grant No. 61505178).

Cuprous oxide (Cu2O) has attracted plenty of attention for potential nonlinear photonic applications due to its superior third-order nonlinear optical property such as two-photon absorption. In this paper, we investigated the two-photon excitation induced carrier dynamics of a Cu2O thin film prepared by radio-frequency magnetron sputtering, using the femtosecond transient absorption experiments. Biexponential dynamics including an ultrafast carrier scattering (< 1 ps) followed by a carrier recombination (> 50 ps) were observed. The time constant of carrier scattering under two-photon excitation is larger than that under one-photon excitation, due to the different transition selection rules and smaller absorption coefficient of the two-photon excitation.

Characterization of NADH fluorescence properties under one-photon excitation with respect to temperature, pH, and binding to lactate dehydrogenase.

Reduced nicotinamide adenine dinucleotide (NADH) is the principal electron donor in glycolysis and oxidative metabolism and is thus recognized as a key biomarker for probing metabolic state. While the fluorescence characteristics of NADH have been investigated extensively, there are discrepancies in the published data due to diverse experimental conditions, instrumentation and microenvironmental parameters that can affect NADH fluorescence. Using a cuvette-based time-resolved spectrofluorimeter employing one-photon excitation at 375 nm, we characterized the fluorescence intensity, lifetime, spectral response, anisotropy and time-resolved anisotropy of NADH in aqueous solution under varying microenvironmental conditions, namely temperature, pH, and binding to lactate dehydrogenase (LDH). Our results demonstrate how temperature, pH, and binding partners each impact the fluorescence signature of NADH and highlight the complexity of the fluorescence data when different parameters produce competing effects. We hope that the data presented in this study will provide a reference for potential sources of variation in experiments measuring NADH fluorescence.