Further time-resolved spectroscopic investigations on the intramolecular charge transfer state of 4-dimethylaminobenzonitrile (DMABN) and its derivatives, 4-diethylaminobenzonitrile (DEABN) and 4-dimethylamino-3,5-dimethylbenzonitrile (TMABN)Dedicated to Professor Dr Z. R. Grabowski and Professor Dr J. Wirz on the occasions of their 75th and 60th birthdays.

Kwok, Wai Ming; Ma, Chensheng; George, Michael W.; Grills, David C.; Matousek, Pavel; Parker, Anthony W.; Phillips, David; Toner, W. T.; Towrie, Michael

doi:10.1039/b209621h

Cited by 33 publications

(43 citation statements)

References 60 publications

(154 reference statements)

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“…Moreover the time-resolved Raman spectra of the ICT state, obtained by using a probe (Raman-inducing) wavelength of 400 nm, exhibit several characteristic modes that are very similar to the modes observed for the benzonitrile radical anion. 35 These results strongly indicate that the ICT transient observed in the time-resolved absorption experiment is the zwitterionic TICT state, in which 90°twisted geometry of the Role of the πσ* State in Molecular Photophysics Zgierski et al amino group with respect to the benzene ring leads to electronic decoupling of the dimethylamino and benzonitrile moieties. The picosecond rise time (4.3 ps) of the TICT-state absorption at 420 nm is identical to the decay time of the πσ*-state absorption at 680 nm for DMABN in acetonitrile, 31,36 Figure 10d,e, thus establishing the precursor-successor relationship between the two states.…”

Section: 17mentioning

confidence: 83%

Role of the πσ* State in Molecular Photophysics

2010

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P hotosynthesis, which depends on light-driven energy and electron transfer in assemblies of porphyrins, chlorophylls, and carotenoids, is just one example of the many complex natural systems of photobiology. A fuller understanding of the spectroscopy and photophysics of simple aromatic molecules is central to elucidating photochemical processes in the more sophisticated assemblies of photobiology. Moreover, developing a better grasp of the photophysics of simple aromatic molecules will also enhance our ability to create and improve practical applications in photochemical energy conversion, molecular nanophotonics, and molecular electronics. In this Account, we present a concerted experimental and theoretical study of aromatic ethynes, aromatic nitriles, and fluorinated benzenes, illustrating the important roles that the low-lying πσ* state plays in the electronic relaxation of these aromatic compounds.Diphenylacetylene, 4-dialkylaminobenzonitriles, 4-dialkylaminobenzethynes, and fluorinated benzenes exhibit fluorescence that strongly quenches as the excitation energy is increased for gas-phase systems and at elevated temperatures in solution. Much of this interesting photophysical behavior can be attributed to the presence of a dark intermediate state that crosses the fluorescent ππ* state. Our quantum chemistry calculations, as well as time-resolved laser spectroscopies, indicate that this dark intermediate state is the πσ* state that arises from the promotion of an electron from the π orbital of the phenyl ring to the σ* orbital localized in the CtX group (where X is CH and N) or on the CsX group (where X is a halogen). These crossings not only lead to the strong excitation energy and temperature dependence of fluorescence but also induce highly interesting πσ*-mediated intramolecular charge transfer in 4-dialkylaminobenzonitriles.Most previous studies on the excited-state dynamics of organic molecules have examined aromatic hydrocarbons, nitrogen heterocycles, aromatic carbonyl compounds, and polyenes, which have low-lying excited states of ππ* character (hydrocarbons and polyenes) or nπ* and ππ* character (carbonyls and N-heterocycles). These studies have revealed important involvement of selection rules (promoting vibrational modes and spin-orbit coupling) and Franck-Condon factors for radiationless transitions, which have important effects on photophysical properties. The recent experimental and time-dependent density functional theory (TDDFT) calculations of aromatic ethynes, nitriles, and perfluorinated benzenes described in this Account demonstrate the importance of the bound excited state of a πσ* configuration in these molecules.

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Section: 17mentioning

confidence: 83%

Role of the πσ* State in Molecular Photophysics

2010

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“…TICT refers to an intramolecular electron transfer which occurs after photoexcitation in donor–π–acceptor molecules. Here, we focus DMABP which pertains to a number of organic molecules representing an intramolecular donor–π–acceptor system which can also undergo TICT . According to more recent findings, these molecules reorient their donor groups (here NMe 2 ) or the whole donor–π moiety (phenyl–NMe 2 ) in the excited state with respect to the π‐acceptor system or the acceptor, the phenylcarbonyl entity.…”

Section: Methodsmentioning

confidence: 99%

“…TICT refers to an intramolecular electron transfer which occurs after photoexcitation in donor-p-acceptor molecules.H ere, we focus DMABPw hichp ertains to a number of organic molecules representing an intramolecular donor-p-acceptors ystem which can also undergo TICT. [18][19][20][21][22][23][24] According to more recent findings, [19,25] these molecules reorient their donor groups (here NMe 2 )o rt he whole donor-p moiety (phenyl-NMe 2 )i nt he excited state with respectt ot he p-acceptor system or the acceptor, the phenylcarbonyl entity. This reorientation leads to at wist of the molecule in the electronically excited singlet state that can be regardeda sa na diabatic photoreaction within the potentials urface.…”

mentioning

confidence: 94%

Significant Fluorescence Enhancement of N,N‐Dimethylaminobenzophenone after Embedding as a C‐Nucleoside in DNA

et al. 2017

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N,N‐dimethylaminobenzophenone (DMABP) represents an intramolecular donor–π–acceptor system resulting in luminescent properties that are highly sensitive to the local surrounding due to twisted intramolecular charge transfer (TICT). In this study, DMABP was covalently linked to a single (ss) or double‐stranded (ds) DNA and studied by a combination of UV/Vis absorption and fluorescence spectroscopy as well as femtosecond pump–probe measurements. As a result of embedding DMABP into a DNA environment, a drastic increase of the fluorescence quantum yield (QY) by a factor of more than 100 was detected, as further evidenced by an increase of the lifetime of the relevant excited states from less than 10 ps to more than 100 ps. A direct comparison between the ss‐ and ds‐DNA systems further demonstrates the high sensitivity to the surrounding area by means of a two‐fold difference in QY and fluorescence lifetimes. As a consequence, the respective DNA moiety (stacking and folding knot) affects significantly the competition between radiationless relaxation processes and fluorescence by interacting with DMABP.

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“…While the structures of the LE and ICT states are still disputed [90]). [89,[91][92][93], the difference between the properties of the excited state in protic and aprotic solvents is of interest and is amenable to study by time-resolved infrared (TRIR) measurements [89,90]. For DMABN in the protic solvent methanol (MeOH), the carbon-nitrogen triple bond IR absorption band develops from an initial single band into a doublet.…”

Section: Time-resolved Vibrational Spectroscopymentioning

confidence: 99%

A lifetime in photochemistry; some ultrafast measurements on singlet states

Phillips¹

2016

Proc. R. Soc. A.

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We describe here the development of time-correlated single-photon counting techniques from the early use of spark discharge lamps as light sources through to the use of femtosecond mode-locked lasers through the personal work of the author. We used laser-excited fluorescence in studies on energy migration and rotational relaxation in synthetic polymer solutions, in biological probe molecules and in supersonic jet expansions. Time-correlated single-photon counting was the first method used in early fluorescence lifetime imaging microscopy (FLIM), and we outline the development of this powerful technique, with a comparison of techniques including wide-field microscopy. We employed these modern forms of FLIM to study single biological cells, and applied FLIM also to gain an understanding the distribution in tissue, and fates of photosensitizer molecules used in photodynamic therapy. We also describe the uses and instrumental design of laser systems for the study of ultrafast time-resolved vibrational spectroscopy.

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Cited by 33 publications

References 60 publications

Role of the πσ* State in Molecular Photophysics

Role of the πσ* State in Molecular Photophysics

Significant Fluorescence Enhancement of N,N‐Dimethylaminobenzophenone after Embedding as a C‐Nucleoside in DNA

A lifetime in photochemistry; some ultrafast measurements on singlet states

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