Time-resolved spectroscopy study of the triplet state of 4-diethylaminobenzonitrile (DEABN)

Kwok, Wai Ming; Ma, Chensheng; Matousek, Pavel; Parker, Anthony W.; Phillips, David; Toner, W. T.; Towrie, Michael; Zuo, Peng; Phillips, David Lee

doi:10.1039/b304896a

Cited by 12 publications

(14 citation statements)

References 52 publications

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“…Because ICT contributes to the S 1 state in the other solvents, the quantum yield for triplet formation decreases significantly, and triplet signals are not observed. There is precedence for this in the literature . Additionally, if excited-state twisting is indeed occurring the ICT triplet can be higher than the singlet, preventing intersystem crossing (ISC) .…”

Section: Results and Discussionmentioning

confidence: 99%

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Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

et al. 2014

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Three two-photon absorption (2PA) dyes (donor-π-donor (DPA2F), donor-π-acceptor (AF240), and acceptor-π-acceptor (BT2F); specifically, D is Ph2N-, A is 2-benzothiazoyl, and the π-linker is 9,9-diethylfluorene) are examined in a variety of aprotic solvents. Because the 2PA cross section is sensitive to the polarity of the local environment, this report examines the solvent-dependent linear photophysics of the dyes, which are important to understand before probing more complex solid-state systems. The symmetrical dyes show little solvent dependence; however, AF240 has significant solvatochromism observed in the fluorescence spectra and lifetimes and also the transient absorption spectra. A 114 nm bathochromic shift is observed in the fluorescence maximum when going from n-hexane to acetonitrile, whereas the lifetimes increase from 1.25 to 3.12 ns. The excited-state dipole moment for AF240 is found to be 20.1 D using the Lippert equation, with smaller values observed for the symmetrical dyes. Additionally, the femtosecond transient absorption (TA) spectra at time zero show little solvent dependence for DPA2F or BT2F, but AF240 shows a 52 nm hypsochromic shift from n-hexane to acetonitrile. Coupled with the solvatochromism in the fluorescence and large excited-state dipole moment, this is attributed to formation of an intramolecular charge-transfer (ICT) state in polar solvents. By 10 ps in AF240, the maximum TA in acetonitrile has shifted 30 nm, providing direct evidence of a solvent-stabilized ICT state, whose formation occurs in 0.85-2.71 ps, depending on solvent. However, AF240 in nonpolar solvents and the symmetrical dyes in all solvents show essentially no shifts due to a predominantly locally excited (LE) state. Preliminary temperature-dependent fluorescence using frozen glass media supports significant solvent reorganization around the AF240 excited state in polar solvents, and may also support a twisted intramolecular charge-transfer (TICT)-state contribution to the stabilization. Finally, time-dependent density functional theory calculations support ICT in AF240 in polar media and also allow prediction of the 2PA cross sections in the 0-0 band, which are much larger for AF240 than the symmetrical dyes.

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Section: Results and Discussionmentioning

confidence: 99%

“…There is precedence for this in the literature. 48 Additionally, if excited-state twisting is indeed occurring the ICT triplet can be higher than the singlet, preventing intersystem crossing (ISC). 49 Our group did previously observe a triplet signal for AF240 in THF.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

et al. 2014

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“…Time-resolved resonance Raman (TR 3 ) may obtain clear structural information from resonance Raman spectra that are convincing enough to provide direct pieces of evidence to distinguish among temporal and structurally similar reactive intermediates, especially those that have overlapped absorption spectra in LFP measurements. Therefore, TR 3 is a powerful method to identify the intermediates generated and to monitor their corresponding kinetics of the short-lived species produced in the different time scale processes. − …”

Section: Introductionmentioning

confidence: 99%

Time-Resolved Spectroscopic and Density Functional Theory Study of the Photochemistry of Irgacure-2959 in an Aqueous Solution

Liu

Xue

et al. 2014

J. Phys. Chem. A

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The photocleavage reaction mechanism of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (Irgacure-2959) was investigated using femtosecond (fs) and nanosecond (ns) transient absorption (-TA) spectroscopy and also picosecond (ps) and nanosecond (ns) time-resolved resonance Raman (-TR(3)) spectroscopy experiments in a water-rich (volume ratio of acetonitrile/water = 3:7) solution. TA spectroscopy was used to study the dynamics of the benzoyl radical growth and decay as well as to investigate the radical quenching process by the radical scavenger methyl acrylate. ps- and ns-TR(3) spectroscopies were employed to monitor the formation of the benzoyl radical and also to characterize its electronic and structural properties. The fs-TA experiments results indicate that the Irgacure-2959 lowest lying excited singlet state S1 underwent efficient intersystem crossing (ISC) to convert into its triplet state with a time constant of 4 ps. Subsequently, this triplet species dissociated into the benzoyl and alkyl radicals with a corresponding maximum absorption band at 415 nm. The TR(3) results in conjunction with results from DFT calculations confirmed that Irgacure-2959 cleaved into the benzoyl and alkyl radicals at a fast rate on the tens of picosecond time scale.

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“…In addition, limitations imposed by most experiments to date provide little information about an ultrafast photophysical or photochemical process occurring immediately after photoexcitation of the molecule. It is well-known that time-resolved resonance Raman (TR 3 ) spectroscopy is a very powerful diagnostic approach to identify and monitor the kinetics of a short-lived reactive intermediate produced in various photoexcited processes. − This method yields direct structural information and can distinguish among multiple and similar intermediates having overlapping absorption spectra. In this sense, the technique is particularly suitable for investigating the phenacyl photo-deprotection reaction since previous transient absorption work found that the intermediates involved show strongly overlapping absorption bands. ,, By detecting directly the structure and kinetics of the transient species using the TR 3 method, our long-term goal seeks to construct the overall mechanism for the phenacyl deprotection and rearrangement reaction.…”

Section: Introductionmentioning

confidence: 99%

Time-Resolved Resonance Raman Study of the Triplet State of the p-Hydroxyphenacyl Acetate Model Phototrigger Compound

Chan

Kwok

et al. 2004

J. Phys. Chem. B

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Picosecond and nanosecond time-resolved resonance Raman spectroscopy have been used to study the dynamics and structure of the phototrigger compound p-hydroxyphenacyl acetate (HPA) in acetonitrile solution. An intermediate was observed that exhibited significant quenching by oxygen. This intermediate was identified and attributed to the ππ* triplet state of HPA. Temporal evolution at early picosecond times indicates rapid intersystem crossing conversion and subsequent relaxation of the excess energy of the initially formed triplet state. B3LYP/6-311G** density functional theory (DFT) calculations were done to determine the structures and vibrational frequencies for both the HPA triplet and ground states. The experimental and theoretical results were compared and discussed in relation to the initial pathway for the p-hydroxyphenacyl deprotection reaction and the nature of the triplet state relative to other aromatic carbonyl compounds. The present results demonstrate the utility of applying ultrafast vibrational spectroscopy to study the mechanism of the photorelease process in phototrigger compounds.

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Time-resolved spectroscopy study of the triplet state of 4-diethylaminobenzonitrile (DEABN)

Cited by 12 publications

References 52 publications

Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

Symmetry- and Solvent-Dependent Photophysics of Fluorenes Containing Donor and Acceptor Groups

Time-Resolved Spectroscopic and Density Functional Theory Study of the Photochemistry of Irgacure-2959 in an Aqueous Solution

Time-Resolved Resonance Raman Study of the Triplet State of the p-Hydroxyphenacyl Acetate Model Phototrigger Compound

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