Excited State Configurations Research Articles

Achievement of persistent and efficient organic room-temperature phosphorescence with temperature-response by adjusting the proportion of excited-state configurations in coupled molecules

Achieving the bright pRTP compound OMe-SPhT with temperature-response by adjusting the proportion of excited-state configurations in coupled molecules.

Transition Metal Complexes and Photodynamic Therapy from a Tumor-Centered Approach: Challenges, Opportunities, and Highlights from the Development of TLD1433.

Transition metal complexes are of increasing interest as photosensitizers in photodynamic therapy (PDT) and, more recently, for photochemotherapy (PCT). In recent years, Ru(II) polypyridyl complexes have emerged as promising systems for both PDT and PCT. Their rich photochemical and photophysical properties derive from a variety of excited-state electronic configurations accessible with visible and near-infrared light, and these properties can be exploited for both energy- and electron-transfer processes that can yield highly potent oxygen-dependent and/or oxygen-independent photobiological activity. Selected examples highlight the use of rational design in coordination chemistry to control the lowest-energy triplet excited-state configurations for eliciting a particular type of photoreactivity for PDT and/or PCT effects. These principles are also discussed in the context of the development of TLD1433, the first Ru(II)-based photosensitizer for PDT to enter a human clinical trial. The design of TLD1433 arose from a tumor-centered approach, as part of a complete PDT package that includes the light component and the protocol for treating non-muscle invasive bladder cancer. Briefly, this review summarizes the challenges to bringing PDT into mainstream cancer therapy. It considers the chemical and photophysical solutions that transition metal complexes offer, and it puts into context the multidisciplinary effort needed to bring a new drug to clinical trial.

Origin of Panchromaticity in Multichromophore-Tetrapyrrole Arrays.

Panchromatic absorbers that have robust photophysical properties enable new designs for molecular-based light-harvesting systems. Herein, we report experimental and theoretical studies of the spectral, redox, and excited-state properties of a series of perylene-monoimide-ethyne-porphyrin arrays wherein the number of perylene-monoimide units is stepped from one to four. In the arrays, a profound shift of absorption intensity from the strong violet-blue (B y and B x) bands of typical porphyrins into the green, red, and near-infrared (Q x and Q y) regions stems from mixing of chromophore and tetrapyrrole molecular orbitals (MOs), which gives multiplets of MOs having electron density spread over the entire array. This reduces the extensive mixing between porphyrin excited-state configurations and the transition-dipole addition and subtraction that normally leads to intense B and weak Q bands. Reduced configurational mixing derives from moderate effects of the ethyne and perylene on the MO energies and a more substantial effect of electron-density delocalization to reduce the configuration-interaction energy. Quantitative oscillator-strength analysis shows that porphyrin intensity is also shifted into the perylene-like green-region absorption and that the ethyne linkers lend absorption intensity. The reduced porphyrin configurational mixing also endows the S1 state with bacteriochlorin-like properties, including a 1-5 ns lifetime.

Intruder configurations of excited states in the neutron-rich isotopes P33 and P34

Author(s): Lubna, RS; Tripathi, V; Tabor, SL; Tai, PL; Kravvaris, K; Bender, PC; Volya, A; Bouhelal, M; Chiara, CJ; Carpenter, MP; Janssens, RVF; Lauritsen, T; McCutchan, EA; Zhu, S; Clark, RM; Fallon, P; MacChiavelli, AO; Paschalis, S; Petri, M; Reviol, W; Sarantites, DG | Abstract: Excited states in the neutron-rich isotopes P33 and P34 were populated by the O18+O18 fusion-evaporation reaction at Elab=24 MeV. The Gammasphere array was used along with the Microball particle detector array to detect γ transitions in coincidence with the charged particles emitted from the compound nucleus S36. The use of Microball enabled the selection of the proton emission channel. It also helped in determining the exact position and energy of the emitted proton; this was later employed in kinematic Doppler corrections. 16 new transitions and 13 new states were observed in P33 and 21 γ rays and 20 energy levels were observed in P34 for the first time. The nearly 4π geometry of Gammasphere allowed the measurement of γ-ray angular distributions leading to spin assignments for many states. The experimental observations for both isotopes were interpreted with the help of shell-model calculations using the (0+1)ω PSDPF interaction. The calculations accounted for both the 0p-0h and 1p-1h states reasonably well and indicated that 2p-2h excitations might dominate the higher-spin configurations in both P33 and P34.

Role of Bath Fluctuations in the Double-Excitation Manifold in Shaping the 2DES of Bacterial Reaction Centers at Low Temperature.

Spectroscopically relevant properties in photosynthetic reaction centers change during charge separation. In this paper, we focus on incorporation of the complete set of environmental fluctuations in the modeling of the nonlinear spectra of molecular aggregates. The model is applied in simulations of two-dimensional electronic spectra of a photosynthetic reaction center at low temperature (5 K), where spectral lines are narrow, such that more features can be resolved. We show that vertical cross sections of the simulated two-dimensional spectra (with all populations in the lowest excited state) reveal transient hole-burned spectra excited resonantly within the B band in agreement with experiment, thus providing new insight into environmental fluctuation parameters of Rhodobacter sphaeroides at low temperatures. Correlated fluctuations of molecular parameters are found to be necessary to describe charge separated configurations of molecular excited states.

Intruder configurations of excited states in the neutron-rich isotopes P 33 and P 34

Intruder configurations of excited states in the neutron-rich isotopes P 33 and P 34

Spectroscopic properties of Pr3+-doped 20Al(PO3)3-80LiF glasses as potential scintillators for neutron detection

We investigate the spectroscopic properties of praseodymium (Pr3+)-doped APLF glasses [20Al(PO3)3−80LiF+xPrF3, x=0.5 to3.0mol%] to realize their potential application as scintillators for neutron detection. From the ultraviolet (UV) to the near infrared (NIR) region, the Pr3+-doped glasses exhibit absorption and emission peaks which correspond to the different interconfigurational 4f5d and intraconfigurational 4f transitions of Pr3+ ions usually located within different environments of the glass matrix. The spectroscopy results also indicate that Pr3+ ions in APLF have a 4f5d excited state configuration which overlaps with the 1S0 level of the 4f ground state configuration. Under 217 nm excitation, the 267 nm emissions of the Pr3+-doped APLF glasses which correspond to the 4f5d → 3H6 transition have fast lifetimes ranging from 16.0 to 19.7ns. In contrast with emission intensities, the emission lifetimes are found to depend only on the doping concentration and not on the sample temperature. Our results suggest that Pr3+-doped APLF glasses can be used as neutron scintillators with robustness in a wide temperature range and with fast and intense emissions at low operating temperatures.

Direct evidence of fadeout of collective enhancement in nuclear level density

The phenomenon of collective enhancement in nuclear level density and its fadeout has been probed using neutron evaporation study of two strongly deformed (173Lu, 185Re), and one spherical (201Tl) compound nuclei over the excitation energy (E⁎) range of ∼22–56 MeV. Clear signature of the fadeout of collective enhancement in nuclear level density was observed for the first time in both the deformed evaporation residues 172Lu and 184Re at an excitation energy range ∼14–21 MeV. Calculations based on finite temperature density functional theory, as well as macroscopic–microscopic shape transition model, have strongly established a close correlation between the observed fadeout of collective enhancement and a deformed to spherical nuclear shape transition in these nuclei occurring in the same excitation energy zone. Interestingly, a weak signature of fadeout has also been observed for the spherical residue 200Tl. This is due to a similar shape transition of the deformed excited state configuration of 200Tl.

Transposed Paternò-Büchi Reaction.

A complementary strategy of utilizing ππ* excited state of alkene instead of nπ* excited state of the carbonyl chromophore in a "transposed Paternò-Büchi" reaction is evaluated with atropisomeric enamides as the model system. Based on photophysical investigations, the nature of excited states and the reactive pathway was deciphered leading to atropselective reaction. This new concept of switching of excited-state configuration should pave the way to control the stereochemical course of photoreaction due to the orbital approaches required for photochemical reactivity.

Characterizing the electronic states of the second-row transition metal cations using high-resolution ion mobility mass spectrometry

Reduced mobilities for ground-state and electronic excited-state configurations of the second-row transition metal cations, excluding Tc+, have been measured. These values were obtained using an ion mobility mass spectrometer that utilizes a 2m drift tube to generate high-resolution ion mobility data. Several of these atomic cations have been previously studied and the results obtained here are compared to reduced mobilities reported in the literature. In all cases, ions were generated using pulsed-laser vaporization of either a metal rod or foil target. Presented here for the first time are the reduced mobilities of Y+, Ru+, and Rh+. A discussion of the observed trends in the mobilities of the second-row transition metal series, relative to those measured for the first-row series, is also provided.

Probing electron correlation through radiative lifetime measurements upon inner-valence photoionization of Ne and Ar

This work demonstrates that electron correlation can have a strong effect on the radiative lifetime of atoms. We report measurements of the radiative lifetimes of inner-valence hole states, the 3s3p6 2S1/2 state of Ar+ and the 2s2p6 2S1/2 state of Ne+ by using the time-correlated single photon counting technique combined with photoionization by synchrotron radiation. Theoretical calculations utilizing the multi-configuration Dirac–Fock method agreed well with the experimental results. In particular, the radiative lifetime was found to depend very sensitively on the mixing of valence excited state configurations. While the Ne+ 2s2p6 2S1/2 state only has relatively weak inter-shell correlation, Ar+ 3s3p6 2S1/2 state has strong intra-shell correlation within the M-shell. This intra-shell correlation enhances configuration mixing and causes the radiative lifetime of the Ar+ 3s3p6 2S1/2 state to become very much longer than that of the Ne+ 2s2p6 2S1/2 state.

Ab initio molecular dynamics simulation study of successive hydrogenation reactions of carbon monoxide producing methanol.

Doing ab initio molecular dynamics simulations, we demonstrate a possibility of hydrogenation of carbon monoxide producing methanol step by step. At first, the hydrogen atom reacts with the carbon monoxide molecule at the excited state forming the formyl radical. Formaldehyde was formed after adding one more hydrogen atom to the system. Finally, absorption of two hydrogen atoms to formaldehyde produces methanol molecule. This study is performed by using the all-electron mixed basis approach based on the time dependent density functional theory within the adiabatic local density approximation for an electronic ground-state configuration and the one-shot GW approximation for an electronic excited state configuration.

Extraction of phase shifts from ensemble densities for composite system scattering

A simple approach for low energy electron scattering by a composite target is presented in which the compound system is described by the ensemble densities and the scattering phase deduced from the quantum defects (QDT). Full calculation of the scattering wave functions is not needed. The ensemble density functional describes the interacting many-fermion bound system, in terms of the first-order densities which represent the ground and several excited state configurations, provided an accurate correlation energy is available. In particular, each configuration is composed of the common set of base core orbitals and single valence orbitals. The valence orbital energies can then be used to deduce the QDT, which are then extrapolated above the scattering threshold energy to obtain the phase shift. Alternatively, the slowly varying single particle potential that generates the orbitals can directly be adopted in the extrapolation; this can lead to a genuine ensemble density approach for scattering states. The inelastic scattering is also studied, which requires the density with one hole orbital in the core set. The importance of the dynamic correlations, including the long-range polarization, is stressed.

Ion Mobility Mass Spectrometry: The design of a new high-resolution ion mobility instrument with applications toward electronic-state characterization of first-row transition metal cations

The design of an instrument that couples a 2-m-long, high-resolution ion mobility drift tube with a quadrupole mass spectrometer is described. The system has been designed to be capable of separating/resolving ionic species having collision cross sections that differ by approximately 1%. Ion funnels are positioned at both the entrance and exit of the drift tube to maximize ion transmission into and out of the drift region of the system. The quadrupole mass analyzer has a mass range of m/z=1–500. To characterize the performance of the instrument, the reduced mobilities for both the ground-state and electronic excited-state configurations of the first-row transition metal cations have been measured. The results obtained are compared to reduced mobilities previously reported. In all cases, ions were generated using pulsed-laser vaporization of metal targets. The reduced mobility of Sc+ is presented here for the first time. A discussion of the relative merits of short and long drift–length mobility instruments is included, as well as an examination of the accuracy expected in the present instrument.

Integration of Cyanine, Merocyanine and Styryl Dye Motifs with Synthetic Bacteriochlorins.

Understanding the effects of substituents on spectral properties is essential for the rational design of tailored bacteriochlorins for light-harvesting and other applications. Toward this goal, three new bacteriochlorins containing previously unexplored conjugating substituents have been prepared and characterized. The conjugating substituents include two positively charged species, 2-(N-ethyl 2-quinolinium)vinyl- (B-1) and 2-(N-ethyl 4-pyridinium)vinyl- (B-2), and a neutral group, acroleinyl- (B-3); the charged species resemble cyanine (or styryl) dye motifs whereas the neutral unit resembles a merocyanine dye motif. The three bacteriochlorins are examined by static and time-resolved absorption and emission spectroscopy and density functional theoretical calculations. B-1 and B-2 have Qy absorption bathochromically shifted well into the NIR region (822 and 852 nm), farther than B-3 (793 nm) and other 3,13-disubstituted bacteriochlorins studied previously. B-1 and B-2 have broad Qy absorption and fluorescence features with large peak separation (Stokes shift), low fluorescence yields, and shortened S1 (Qy ) excited-state lifetimes (~700 ps and ~100 ps). More typical spectra and S1 lifetime (~2.3 ns) are found for B-3. The combined photophysical and molecular-orbital characteristics suggest the altered spectra and enhanced nonradiative S1 decay of B-1 and B-2 derive from excited-state configurations in which electron density is shifted between the macrocycle and the substituents.

Excited-to-excited-state scattering using weak measurements

Weak measurements are a subset of measurement processes in quantum mechanics wherein the system, which is being measured, interacts very weakly with the measuring apparatus. Measurement values of observables undergoing a weak interaction and their amplification are concepts that have sharpened our understanding of interaction processes in quantum mechanics. Recent experiments show that naturally occurring processes such as resonance fluorescence from excited states of an atom can exhibit weak value amplification effect. In this paper we theoretically analyze the process of elastic resonance fluorescence from a $\mathsf{V}$-type three-level atomic system, using the well-known Weiskopff-Wigner (WW) theory of spontaneous emission. Within this theory we show that a weak interaction regime can be identified and for suitable choices of initial and final excited states the mean scattering time between these states show an amplification effect during interaction with the vacuum bath modes of the electromagnetic field. We thus show that a system-bath interaction can show weak value amplification. Using our theory we reproduce the published experimental results carried out in such a system. More importantly, our theory can calculate scattering time scales in elastic resonance scattering between multiple excited states of a single atom or between common excited state configurations of interacting multiatom systems.

On the relation between adiabatic time dependent density functional theory (TDDFT) and the ΔSCF-DFT method. Introducing a numerically stable ΔSCF-DFT scheme for local functionals based on constricted variational DFT

In ΔSCF density functional theory studies of a i → a transition one performs separate fully self-consistent field calculations on the ground state configuration (i)n (n = 1,2) and the excited state configuration (i)n − 1a. The excitation energy for the transition i → a is subsequently determined as the Kohn-Sham energy difference ΔEi → a = E[in − 1a] − E[in] between the ground state (i)n and the excited state configuration (i)n − 1a. The ΔSCF scheme has been applied extensively and works well for lower energy excitations provided that they can be represented by a single orbital replacement or transition i → a. However, for excitations of higher energy ΔSCF tends to become numerically unstable with a variational collapse to transitions of lower energy. We demonstrate here a numerically stable ΔSCF scheme for local functionals that is guaranteed not to collapse on excited configurations of lower energy as well as the ground state. The new scheme is based on constricted variational density functional theory in which the canonical ground state orbitals are allowed to relax (R-CV(∞)-DFT). Since it is restricted to a single orbital replacement i → a it is termed SOR-R-CV(∞)-DFT.

A soluble cryogenic thermometer with high sensitivity based on excited-state configuration transformations.

Cryogenic temperature detection plays an irreplaceable role in exploring nature. Developing high sensitivity, accurate, observable and convenient measurements of cryogenic temperature is not only a challenge but also an opportunity for the thermometer field. The small molecule 9-(9,9-dimethyl-9H-fluoren-3yl)-14-phenyl-9,14-dihydrodibenzo[a,c]phenazine (FIPAC) in 2-methyl-tetrahydrofuran (MeTHF) solution is utilized for the detection of cryogenic temperature with a wide range from 138 K to 343 K. This system possesses significantly high sensitivity at low temperature, which reaches as high as 19.4% K(-1) at 138 K. The temperature-dependent ratio of the dual emission intensity can be fitted as a single-exponential curve as a function of temperature. This single-exponential curve can be explained by the mechanism that the dual emission feature of FIPAC results from the excited-state configuration transformations upon heating or cooling, which is very different from the previously reported mechanisms. Here, our work gives an overall interpretation for this mechanism. Therefore, application of FIPAC as a cryogenic thermometer is experimentally and theoretically feasible.

Synthesis and investigation of intra-molecular charge transfer state properties of novel donor-acceptor-donor pyridine derivatives: the effects of temperature and environment on molecular configurations and the origin of delayed fluorescence.

A novel series of donor-acceptor-donor (D-A-D) structured pyridine derivatives were synthesised and detailed photo-physical investigations were made using mainly steady-state and time-resolved spectroscopy techniques at varying temperatures. The investigations showed that the molecules have solvent polarity and temperature dependent excited-state configurations, confirmed in two different polarity solvents (295-90 K), i.e. methyl cyclohexane (MCH) and 2-methyltetrahdrofurane (2-MeTHF). In MCH, the investigations revealed dual fluorescence over the temperature range of 295-90 K. At 295 K, the ground-state configuration of the molecules has a partially twisted geometry as determined by DFT calculation, yet the emission originates totally from a locally excited (LE) state, however once the temperature is lowered to 90 K, the twisted molecular configuration is stabilised, and the emission originates from a fully-relaxed intramolecular charge transfer state (ICT), this is contrary to the systems where structural reorganisation stabilises ICT and this is frozen out at low temperatures. The DFT calculations revealed different ground state molecular configurations due to the presence of different electron-donating groups, e.g. the molecule including anthracene groups has a near 90° twisted geometry whereas the triphenylamine including molecule has a pyramidal geometrical folding, therefore, the decrease in temperature restricts the donor degree of rotational freedom. In 2-MeTHF solution, the fluorescence spectrum of both molecules is always of ICT character, but gradually red-shifts through the fluid to glass transition temperature (∼135 K), in this case, the fluorescence occurs after structural and solvent-shell relaxations, however, upon cooling below 135 K, the spectra dramatically shift back to blue giving rise to strong emission from an ICT excited-state (but not the LE state) where the molecules have unrelaxed geometries. This significant change in the nature of the emitting species was explained with specific solvent-solute dynamic interactions in the vicinity of the solvation shell and the effect of thermal excitation of molecular vibrational modes of the C-C bond linking donor and acceptor units. Finally, we confirmed that the molecules have ICT ground-state geometry in the solid-state phase (spin-coated films), and the time-resolved decay dynamics were investigated comparing the spin-coated films (at RT and 25 K) and MCH solutions (at 295 K and 90 K).

Synthesis and theoretical study on fluorescence property of 4- (2-hydroxybenzylideneamino) phenyl ethanone schiff base

Using salicylaldehyde and 4-aminophenyl ethanone as raw material, a Schiff base derivative 4-(2-hydroxybenzylidene-amino) phenyl ethanone was synthesized by the solid phase reaction method at room temperature. The structure of the product was characterized by elemental analysis and 1 HNMR The UV spectra, fluorescence emission spectra and fluorescence quantum yield of the title Schiff base derivative were investigated. The results showed that this Schiff base displayed superior fluorescence property. The ground state configuration of the title Schiff base was optimized by density functional theory (DFT) method at the B3LYP/6-311G level. After vibrational analysis, there is no imaginary frequency, which indicates that the structure is stable. Then the ground state configuration was optimized to the excited state configuration by the method of single excited interactions CIS. Based on the optimized structure for the ground state and excited state time-dependent density functional theory (TD-DFT) calculations were carried out at the B3LYP/6-31G level to predict the absorption spectra and the fluorescence spectra. The results show that the computed spectra were comparable with the spectra from the experiments. The relationship between the molecular structure and the fluorescence property of 4-(2-hydroxybenzylideneamino) phenyl ethanone was also discussed. The results obtained may provide some theoretical guidance for the design of new fluorescence compounds.