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 Quantum-Chemical Search for Keto Tautomers of Azulenols in Vacuo and Aqueous Solution

Symmetry ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 497
Author(s):  
Ewa D. Raczyńska
Keyword(s):  
Aqueous Solution ◽  
Quantum Chemical ◽  
Biologically Active ◽  
Deprotonation Reaction ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Scanty Information ◽  
Derivatives Of ◽  
Common Anion ◽  
Tautomeric Mixture

Keto-enol prototropic conversions for carbonyl compounds and phenols have been extensively studied, and many interesting review articles and even books appeared in the last 50 years. Quite a different situation takes place for derivatives of biologically active azulene, for which only scanty information on this phenomenon can be found in the literature. In this work, quantum-chemical studies have been undertaken for symmetrically and unsymmetrically substituted azulenols (constitutional isomers of naphthols). Stabilities of two enol (OH) rotamers and all possible keto (CH) tautomers have been analyzed in the gas phase {DFT(B3LYP)/6-311+G(d,p)} and also in aqueous solution {PCM(water)//DFT(B3LYP)/6-311+G(d,p)}. Contrary to naphthols, for which the keto forms can be neglected, at least one keto isomer (C1H, C2H, and/or C3H) contributes significantly to the tautomeric mixture of each azulenol to a higher degree in vacuo (non-polar environment) than in water (polar amphoteric solvent). The highest amounts of the CH forms have been found for 2- and 5-hydroxyazulenes, and the smallest ones for 1- and 6-hydroxy derivatives. The keto tautomer(s), together with the enol rotamers, can also participate in deprotonation reaction leading to a common anion and influence its acid-base properties. The strongest acidity in vacuo exhibits 6-hydroxyazulene, and the weakest one displays 1-hydroxyazulene, but all azulenols are stronger acids than phenol and naphthols. Bond length alternation in all DFT-optimized structures has been measured using the harmonic oscillator model of electron delocalization (HOMED) index. Generally, the HOMED values decrease for the keto tautomers, particularly for the ring containing the labile proton. Even for the keto tautomers possessing energetic parameters close to those of the enol isomers, the HOMED indices are low. However, some kind of parallelism exists for the keto forms between their relative energies and HOMEDs estimated for the entire molecules.

Spectral and Quantum-Chemical Studies of the Band Shape in Absorption of Merocyanine Derivatives of Cyclohexadienone

2017 ◽  
Vol 6 (4) ◽  
pp. 514-523 ◽  
Author(s):  
Ruslan S. Iakovyshen ◽  
Elena L. Pavlenko ◽  
Volodymyr A. Brusentsov ◽  
Oksana P. Dmytrenko ◽  
Mykola P. Kulish ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Band Shape ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Derivatives Of

Spectroscopic and Quantum-Chemical Studies of Halogen-Containing Derivatives of Poly-N-Epoxypropylcarbazole

2018 ◽  
Vol 125 (4) ◽  
pp. 499-505 ◽  
Author(s):  
E. V. Seliverstova ◽  
N. Kh. Ibrayev ◽  
A. K. Nurmakhanova ◽  
D. A. Temirbayeva
Keyword(s):  
Quantum Chemical ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Derivatives Of

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.

Cyanine-Like and Polyenic Relaxation Paths of Merocyanine Derivatives of Malonodinitrile in the Excited State Detecting by Low Temperature Time-Resolved Fluorescence

2012 ◽  
Vol 57 (8) ◽  
pp. 812
Author(s):  
M.M. Sevryukova ◽  
Yu.P. Piryatinski ◽  
S.V. Vasylyuk ◽  
V.M. Yashchuk ◽  
O.O. Viniychuk ◽  
...  
Keyword(s):  
Excited State ◽  
Fluorescence Spectra ◽  
Experimental Studies ◽  
Time Resolved Fluorescence ◽  
Fluorescence Excitation ◽  
Time Resolved ◽  
Electron Transitions ◽  
Anisotropy Spectra ◽  
Derivatives Of ◽  
Temperature Time

The combined quantum-chemical and spectral study of features of the electron transitions in merocyanines is carried out. It is established that the two lowest transitions are split and involve both donor levels, similarly to symmetric cyanines. The long-wave absorption band has high intensity, while the second transition manifests itself only in the fluorescence excitation anisotropy spectra. In contrast to the ground state, the MO splitting in the excited state leads to the instability. The analysis of the results of theoretical and experimental studies enables us to propose that there are two paths of the relaxation in the excited state: a) cyanine-like one with equalizing the bond lengths; b) polyenic one with the considerable bond length alternation. This assumption is confirmed by the existence of two components in the time-resolved fluorescence spectra measured at low temperatures.

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