Experimental Investigation by Laser Flash Photolysis To Reveal the Optical and Electron-Donating Properties of Benzothiazole Derivatives and a Theoretical Approach by Using Time-Dependent Density Functional Theory

Pal, Samir Kumar; Sahu, T.; Misra, T. N.; Mallick, Prabal Kumar; Paddon‐Row, Michael N.; Ganguly, Tapan

doi:10.1021/jp047445k

Cited by 16 publications

(7 citation statements)

References 73 publications

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“…We employed the PBE0 functional for our calculations given that this functional was developed without empirically adjusted parameters and has been shown to be well-suited for the description of the excited-state electronic density of medium-sized organic systems . These methodologies have in fact been proven to be useful in several studies about the relative energy of different electronic states, in particular, assessing the ordering of low-lying singlet and triplet states. − Because our results are strongly dependent on the solvent environment, we have modeled solvation effects on the excited-state energies through the PCM model with the integral equation formalism (IEFPCM). This method to treat the solvent also has been proven to be adequate in the estimation of relative energies of the triplet manifold with respect to the first singlet excited state in different environments. − From previous considerations in similar systems, , both ground-state and excited-state calculations (including geometry optimizations), the 6-311++G (d,p) basis set was employed.…”

Section: Methodsmentioning

confidence: 99%

Role of Upper Triplet States on the Photophysics of Nitrated Polyaromatic Compounds: S₁ Lifetimes of Singly Nitrated Pyrenes

2011

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The photophysics of most nitrated polycyclic aromatic compounds is dominated by an ultrafast intersystem crossing channel, which makes their first singlet excited states decay with rates on the order of 10(12) to 10(13) s(-1). Some questions, however, remain about the nature of the receiver triplet states, which have been in principle assigned to specific triplets of a different electronic configuration from T(1). In particular, it could be suggested that even a small degree of n-π* character of the T(1) state may be enough to allow the S(1) state to couple to upper vibronic states of the lowest energy triplet, without the requirement for specific upper triplet states. In this report, we show that there are, in fact, nitroaromatic compounds that do not show the ultrafast intersystem crossing channel but instead have S(1) states that are two to three orders of magnitude longer lived. Our studies focused on the time resolution of the emission from singly nitrated pyrenes, which show a strong photophysical dependence on the position of the NO(2) group: Whereas S(1) in 1-nitropyrene is short-lived (up to 3 ps), in 4-nitropyrene and 2-nitropyrene this state has 0.41 and 1.2 ns lifetimes, respectively, in acetonitrile solution. Computational work at the TD-DFT level of theory indicates that such remarkable increase in the first excited singlet lifetime can indeed be explained by a loss of the energy coincidence between the S(1) state with specific upper triplet states formed from transitions that involve the nonbonding orbitals at the oxygen atoms. These results are in strong support of the previous descriptions about the requirement for intermediacy of specific triplet states in the ultrafast decay of the fluorescent state present in most nitroaromatics. The implications for the photochemistry of this group of toxic atmospheric pollutants, including the channel that redounds in the dissociation of the NO· fragment, are discussed in view of the present results.

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Section: Methodsmentioning

confidence: 99%

Role of Upper Triplet States on the Photophysics of Nitrated Polyaromatic Compounds: S₁ Lifetimes of Singly Nitrated Pyrenes

2011

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“…Electronic transitions of transient species were calculated by single-point calculations using UB3LYP/6-311-G(d,p) with TD = (Nstates = 15) and SCRF = acetonitrile. A similar approach has been applied successfully to several radical systems. − …”

Section: Methodsmentioning

confidence: 99%

Photoreduction of Oxoisoaporphines by Amines: Laser Flash and Steady-State Photolysis, Pulse Radiolysis, and TD-DFT Studies

et al. 2009

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Photoreduction of oxoisoaporphine (OIA) (1-aza-benzo-[de]anthracen-7-one) and its 5-methoxy (5-MeO-OIA) derivative by selected amines (two non-alpha-hydrogen-donating amines (1,4-diaza[2.2.2]-bicyclooctane (DABCO) and 2,2,6,6-tetramethylpiperidine (TMP)) and three alpha-hydrogen-donating amines (triethylamine (TEA), diethylmethylamine (DEMA), and dimethylethylamine (DMEA))) has been studied in deaerated neat acetonitrile solutions using laser flash and steady-state photolysis. The triplet excited states of OIA and 5-MeO-OIA are characterized by intense absorption maxima located at lambda(max) = 450 nm and lifetimes of 34.7 +/- 0.5 and 44.6 +/- 0.4 micros, respectively. In the presence of tertiary amines, both triplets are quenched with a rate constant that varies from the near diffusion limit (>10(9) M(-1) s(-1)) to a rather low value (approximately 10(7) M(-1) s(-1)) and shows the expected dependence on the reduction potential for one-electron-transfer reactions. The transient absorption spectra observed after quenching of the respective triplet states are characterized by distinct absorption maxima located at lambda(max) = 480 and 490 nm (for OIA and 5-MeO-OIA, respectively) and accompanied by broad shoulders in the range of 510-560 nm. They were assigned to either solvent-separated radical ion pairs and/or isolated radical anions. In the presence of alpha-hydrogen-donating amines these species undergo protonation that leads to the formation of neutral hydrogenated radicals A1H(*)/A2H(*) with two possible sites of protonation, N and O atoms. Pulse radiolysis and molecular modeling together with TD-DFT calculations were used to support the conclusions about the origin of transients.

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“…Thus REPs of different normal modes of vibration may provide information about the structural configuration of the molecule. Moreover, the molecular structures not only in the ground state but also in the excited states play important roles in determining the various photophysical and photochemical properties of molecules 16–24…”

Section: Introductionmentioning

confidence: 99%

Vibrational dynamics and structural investigation of 4‐benzoylpyridine

Sett

Datta

Mallick

2010

J Raman Spectroscopy

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The polarized Raman spectra in different environments along with the IR counterpart of 4-benzoylpyridine (4-BOP) were critically analyzed to assign all of its normal modes of vibration. The knowledge of the positions of different excited electronic states (EESs)was obtained from the study of electronic absorption spectra. Measurement of Raman excitation profiles (REPs)of several normal modes was carried out to get insight into structural and symmetry properties of the molecule. All the experimental observations were substantiated and corroborated theoretically by quantum chemical calculations (QCCs). The possibility of exciton splitting of the 1 L a band has been explored both from theoretical and experimental points of view.

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Experimental Investigation by Laser Flash Photolysis To Reveal the Optical and Electron-Donating Properties of Benzothiazole Derivatives and a Theoretical Approach by Using Time-Dependent Density Functional Theory

Cited by 16 publications

References 73 publications

Role of Upper Triplet States on the Photophysics of Nitrated Polyaromatic Compounds: S₁ Lifetimes of Singly Nitrated Pyrenes

Role of Upper Triplet States on the Photophysics of Nitrated Polyaromatic Compounds: S₁ Lifetimes of Singly Nitrated Pyrenes

Photoreduction of Oxoisoaporphines by Amines: Laser Flash and Steady-State Photolysis, Pulse Radiolysis, and TD-DFT Studies

Vibrational dynamics and structural investigation of 4‐benzoylpyridine

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Experimental Investigation by Laser Flash Photolysis To Reveal the Optical and Electron-Donating Properties of Benzothiazole Derivatives and a Theoretical Approach by Using Time-Dependent Density Functional Theory

Cited by 16 publications

References 73 publications

Role of Upper Triplet States on the Photophysics of Nitrated Polyaromatic Compounds: S1 Lifetimes of Singly Nitrated Pyrenes

Role of Upper Triplet States on the Photophysics of Nitrated Polyaromatic Compounds: S1 Lifetimes of Singly Nitrated Pyrenes

Photoreduction of Oxoisoaporphines by Amines: Laser Flash and Steady-State Photolysis, Pulse Radiolysis, and TD-DFT Studies

Vibrational dynamics and structural investigation of 4‐benzoylpyridine

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Role of Upper Triplet States on the Photophysics of Nitrated Polyaromatic Compounds: S₁ Lifetimes of Singly Nitrated Pyrenes

Role of Upper Triplet States on the Photophysics of Nitrated Polyaromatic Compounds: S₁ Lifetimes of Singly Nitrated Pyrenes