scholarly journals On Anomalous Fluorescence of Symmetrical Polymethine Dyes

2020 ◽  
Vol 2020 ◽  
pp. 1-8
Author(s):  
P. O. Kondratenko ◽  
Yu. M. Lopatkin
Keyword(s):  
Excited States ◽  
Ground State ◽  
Internal Conversion ◽  
Polymethine Dyes ◽  
Necessary Condition ◽  
Relaxation Processes ◽  
Sufficient Condition ◽  
Radiative Relaxation ◽  
Higher Excited States ◽  
Group Theoretical Analysis

The group-theoretical analysis of polymethine dyes (PMD) showed that relaxation processes between the states S3 and S1 are forbidden, either by radiation or by internal conversion. From the state S3, only transition to the ground state of the molecule is possible. Since the experimental data state that the quantum yield of S3 ⟶ S0 fluorescence does not exceed 1%, it is indicated that the internal conversion rate can be 2 orders of magnitude higher than the radiative relaxation rate of the molecule. Concerning the reasons for the appearance of fluorescence from the higher excited states of molecules, it can be asserted that the necessary condition for the appearance of S3 ⟶ S0 fluorescence is the absence of S0 ⟶ S1(v)-absorption in the region of the S0 ⟶ S3 transition. The sufficient condition is the corresponding symmetry of the excited states, which imposes a prohibition on the S3 ⟶ S1 relaxation process.

Evaluation of Luminescence Decay Measurements Probed on Pure and Doped Pt(IV) Hexahalogeno Complexes. II. Molecular Properties Obtained from Temperature Dependent Lifetime Curves

1997 ◽  
Vol 52 (5) ◽  
pp. 447-456
Author(s):  
Ingo Biertümpel ◽  
Hans-Herbert Schmidtke
Keyword(s):  
Excited States ◽  
Ground State ◽  
Energy Levels ◽  
Decay Rates ◽  
Rate Equations ◽  
Temperature Dependent ◽  
Lifetime Measurements ◽  
Thermally Activated ◽  
Ground State Energies ◽  
Higher Excited States

Abstract Lifetime measurements down to nearly liquid helium temperatures are used for determining energy levels and transition rates between excited levels and relaxations into the ground state. Energies are obtained from temperature dependent lifetimes by fitting experimental curves to model functions pertinent for thermally activated processes. Rates are calculated from solutions of rate equations. Similar parameters for pure and doped Pt(IV) hexahalogeno complexes indicate that excited levels largely belong to molecular units. Some of the rates between excited states are only somewhat larger than decay rates into the ground state, which is a consequence of the polyexponential decay measured also at low temperature (2 K). In the series of halogen complexes, the rates between spinorbit levels resulting from 3T1g increase from fluorine to bromine, although energy splittings become larger. Due to the decreasing population of higher excited states in this series, K^PtFö shows a tri-exponential, K2PtCl6 a bi-exponential and FoPtBr6 a mono-exponential decay. In the latter case the population density of higher excited states relaxes so fast that emission occurs primarily from the lowest excited Γ3(3T1g) level. Phase transitions and emission from chromophores on different sites can also be observed.

Excited states of positronium in positron–hydrogen charge exchange

1978 ◽  
Vol 56 (5) ◽  
pp. 565-570 ◽  
Author(s):  
V. S. Kulhar ◽  
C. S. Shastry
Keyword(s):  
Excited States ◽  
Charge Exchange ◽  
Cross Sections ◽  
Ground State ◽  
Born Approximation ◽  
Energy Region ◽  
Hydrogen Charge ◽  
Positronium Formation ◽  
State Approximation ◽  
Higher Excited States

The two state approximation method for the study of the rearrangement collisions is applied to the process of positronium formation in excited states for positron–hydrogen charge exchange collisions. Differential and integrated cross sections are computed for positronium formation in 2S, 2P, and 3S excited states. The results obtained in the energy region 2 to 10 Ry are compared with positronium formation cross sections in ground state. Total positronium formation cross sections including the contributions of capture into all the higher excited states of positronium are also computed in the first Born approximation and the two state approximation in the energy region considered.

Rotational Structure in Some Higher Excited States of the GeF Molecule

1974 ◽  
Vol 52 (15) ◽  
pp. 1458-1475 ◽  
Author(s):  
R. W. Martin ◽  
A. J. Merer
Keyword(s):  
Emission Spectrum ◽  
Excited States ◽  
Ground State ◽  
Valence State ◽  
Rydberg States ◽  
The Other ◽  
Electronic Transitions ◽  
Lower State ◽  
High Dispersion ◽  
Higher Excited States

The weaker electronic transitions in the region 2000–9000 Å in the emission spectrum of GeF have been photographed at high dispersion; three new transitions with the A2Σ+ state as lower state have been discovered, and the various systems near 2100 and 8600 Å have been reassigned. The spectra have been explained in terms of six excited states lying between 40 000 and 50 000 cm−1 above the ground state, and representative bands involving all six have been analyzed rotationally. Five of these excited states are Rydberg states (5pσ, 5pπ, 4dπ, 4dδ, and 6sσ), and the other is the σπ22Δ valence state; this latter interacts strongly with the 4dδ 2Δ state.

scholarly journals Stable Boron-Containing Blue-Photoluminescent Radicals

2021 ◽  
Author(s):  
Zhongtao Feng ◽  
Yuanyuan Chong ◽  
Shuxuan Tang ◽  
Huapeng Ruan ◽  
Yong Fang ◽  
...  
Keyword(s):  
Excited States ◽  
Epr Spectroscopy ◽  
Ground State ◽  
Radiative Decay ◽  
Blue Emission ◽  
X Ray Diffraction ◽  
X Ray ◽  
Stable Radicals ◽  
Higher Excited States ◽  
Blue Photoluminescence

<div>It is highly urgent to develop synthetic strategies to make new category of stable luminescent radicals with desired emission wavelength. In this study, we have isolated two dioxoborocyclic radicals ( <b>3</b> and <b>4</b> ) by a direct sy nthetic rou te. They were charac terized by UV, EPR spectroscopy and SQUID measurements. Their structures were obtained by single crystal X ray diffraction. Both radicals produce blue photoluminescence (458 nm for <b>3</b> and 478 nm for <b>4</b> ) by radiative decay from higher excited states (D<sub>2</sub>/D<sub>3</sub>) to the ground state (D<sub>0</sub>) based on theoretical calculation, breaking Kasha rule. The work records a new kind of radical emitters and the first stable radicals with blue emission bands.</div>

scholarly journals Probing of Higher Excited States of Merocyanine Derivatives of Azaazulene and Indandione by Fluorescence Excitation Anisotropy Spectra

2020 ◽  
Vol 65 (4) ◽  
pp. 321
Author(s):  
A. P. Naumenko ◽  
V. I. Borysuk ◽  
M. S. Iakhnenko ◽  
V. O. Gubanov ◽  
Y. L. Slominskii ◽  
...  
Keyword(s):  
Excited States ◽  
Electronic Transition ◽  
Quantum Chemical ◽  
Bathochromic Shift ◽  
Polymethine Dyes ◽  
Fluorescence Excitation ◽  
Chemical Studies ◽  
Anisotropy Spectra ◽  
Derivatives Of ◽  
Higher Excited States

This paper is dedicated to the spectral and quantum-chemical studies of higher excited states of merocyanine derivatives of azaazulene and indandione. A particular attention is paid to the analysis of fluorescence excitation anisotropy spectra of the mentioned compounds. The long-wave shift by ≈ 50 nm of a deep clear minimum in the fluorescence excitation anisotropy spectrum due to an elongation of the polymethine dye chromophore is established. Such shift is close in a value to the bathochromic shift of the first minimum in the anisotropy spectrum of symmetric ionic polymethine dyes, in which this minimum corresponds to the second electronic transition. The parallel spectral study and quantum-chemical calculations allowed us to correctly interpret the fluorescence excitation anisotropy spectra of merocyanines and relate the first clear minimum with the seventh electronic transition. The last resembles the second electronic transition between delocalized molecular orbitals (MO) in polymethine dyes.

scholarly journals Stable Boron-Containing Blue-Photoluminescent Radicals

2021 ◽  
Author(s):  
Zhongtao Feng ◽  
Yuanyuan Chong ◽  
Shuxuan Tang ◽  
Huapeng Ruan ◽  
Yong Fang ◽  
...  
Keyword(s):  
Excited States ◽  
Epr Spectroscopy ◽  
Ground State ◽  
Radiative Decay ◽  
Blue Emission ◽  
X Ray Diffraction ◽  
X Ray ◽  
Stable Radicals ◽  
Higher Excited States ◽  
Blue Photoluminescence

<div>It is highly urgent to develop synthetic strategies to make new category of stable luminescent radicals with desired emission wavelength. In this study, we have isolated two dioxoborocyclic radicals ( <b>3</b> and <b>4</b> ) by a direct sy nthetic rou te. They were charac terized by UV, EPR spectroscopy and SQUID measurements. Their structures were obtained by single crystal X ray diffraction. Both radicals produce blue photoluminescence (458 nm for <b>3</b> and 478 nm for <b>4</b> ) by radiative decay from higher excited states (D<sub>2</sub>/D<sub>3</sub>) to the ground state (D<sub>0</sub>) based on theoretical calculation, breaking Kasha rule. The work records a new kind of radical emitters and the first stable radicals with blue emission bands.</div>

scholarly journals Observation of Enhanced Dissociative Photochemistry in the Non-Native Nucleobase 2-Thiouracil

Molecules ◽  
2020 ◽  
Vol 25 (14) ◽  
pp. 3157
Author(s):  
Kelechi O. Uleanya ◽  
Rosaria Cercola ◽  
Maria Nikolova ◽  
Edward Matthews ◽  
Natalie G. K. Wong ◽  
...  
Keyword(s):  
Excited States ◽  
Ground State ◽  
Internal Conversion ◽  
Photophysical Properties ◽  
Ionization Mass ◽  
Deprotonated Form ◽  
Fragment Ions ◽  
Protonated Forms ◽  
Electron Ejection ◽  
Triplet Excited States

We present the first study to measure the dissociative photochemistry of 2-thiouracil (2-TU), an important nucleobase analogue with applications in molecular biology and pharmacology. Laser photodissociation spectroscopy is applied to the deprotonated and protonated forms of 2-TU, which are produced in the gas-phase using electrospray ionization mass spectrometry. Our results show that the deprotonated form of 2-thiouracil ([2-TU-H]−) decays predominantly by electron ejection and hence concomitant production of the [2-TU-H]· free-radical species, following photoexcitation across the UVA-UVC region. Thiocyanate (SCN−) and a m/z 93 fragment ion are also observed as photodecay products of [2-TU-H]− but at very low intensities. Photoexcitation of protonated 2-thiouracil ([2-TU·H]+) across the same UVA-UVC spectral region produces the m/z 96 cationic fragment as the major photofragment. This ion corresponds to ejection of an HS· radical from the precursor ion and is determined to be a product of direct excited state decay. Fragment ions associated with decay of the hot ground state (i.e., the ions we would expect to observe if 2-thiouracil was behaving like UV-dissipating uracil) are observed as much more minor products. This behaviour is consistent with enhanced intersystem crossing to triplet excited states compared to internal conversion back to the ground state. These are the first experiments to probe the effect of protonation/deprotonation on thionucleobase photochemistry, and hence explore the effect of pH at a molecular level on their photophysical properties.

Ab Initio-Rechnungen zum F2-Molekül/ Different ab-initio calculations for the ground-state and some excited states of the F2-molecule

1973 ◽  
Vol 28 (5) ◽  
pp. 704-708 ◽  
Author(s):  
E. Kasseckert
Keyword(s):  
Ab Initio ◽  
Excited States ◽  
Ground State ◽  
Good Description ◽  
Basis Functions ◽  
Slater Type Orbitals ◽  
Slater Type ◽  
Ci Calculations ◽  
Potential Curves ◽  
Higher Excited States

For the ground-state and the lower lying excited states of the fluorine-molecule VB -CI calculations with Slater-type orbitals and SCF -CI calculations with contracted Gauß-Lobe functions have been carried out. The SCF -CI method yields a fairly good description of the ground-state. But it is rather difficult to decide whether the SCF -CI calculations of the excited states are accurate or not. The discussion of the potential-curves of some higher excited states leads to the conjecture that the experimentally observed orange band-systems may belong to two transitions1Σg-→ 1Πu and 1Σu+ → 1Πg.But this should be checked in further calculations which must include higher orbitals as basis functions.

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