Excited-state relaxation of bridged and unbridged anilino-pyridinium dyes

Kharlanov, V. A.; Rettig, Wolfgang

doi:10.1016/j.chemphys.2006.11.021

Cited by 9 publications

(13 citation statements)

References 19 publications

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“…[55] The quantum chemical results obtained for this molecule are similar to those of 4, that is, a CT state with full charge localization can be reached by angular relaxation to 908 twist. [56] The results of the DFT calculations (Figures 6 and 7) for 4(M) confirm the full CT nature of the excited state at the orthogonal geometry, with full localization of the positive charge on the donor moiety, consistent with the TICT model. Such a CT state is connected with 1) a strong charge shift; 2) a vanishing transition moment, causing a very small oscillator strength as well as emissive rate constant; 3) a large nonradiative rate constant, causing strong fluorescence quenching; 4) a very close-lying CT triplet state that can also cause fast depopulation of the excited singlet state.…”

Section: Quantum Chemical Calculationssupporting

confidence: 75%

Optical, Redox, and DNA‐Binding Properties of Phenanthridinium Chromophores: Elucidating the Role of the Phenyl Substituent for Fluorescence Enhancement of Ethidium in the Presence of DNA

Prunkl

Pichlmaier

Winter

et al. 2010

Chemistry A European J

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The phenanthridinium chromophores 5-ethyl-6-phenylphenanthridinium (1), 5-ethyl-6-methylphenanthridinium (2), 3,8-diamino-5-ethyl-6-methylphenanthridinium (3), and 3,8-diamino-5-ethyl-6-(4-N,N-diethylaminophenyl)phenanthridinium (4) were characterized by their optical and redox properties. All dyes were applied in titration experiments with a random-sequence 17mer DNA duplex and their binding affinities were determined. The results were compared to well-known ethidium bromide (E). In general, this set of data allows the influence of substituents in positions 3, 6, and 8 on the optical properties of E to be elucidated. Especially, compound 4 was used to compare the weak electron-donating character of the phenyl substituent at position 6 of E with the more electron-donating 4-N,N-diethylaminophenyl group. Analysis of all of the measurements revealed two pairs of chromophores. The first pair, consisting of 1 and 2, lacks the amino groups in positions 3 and 8, and, as a result, these dyes exhibit clearly altered optical and electrochemical properties compared with E. In the presence of DNA, a significant fluorescence quenching was observed. Their binding affinity to DNA is reduced by nearly one order of magnitude. The electronic effect of the phenyl group in position 6 on this type of dye is rather small. The properties of the second set, 3 and 4, are similar to E due to the presence of the two strongly electron-donating amino groups in positions 3 and 8. However, in contrast to 1 and 2, the electron-donating character of the substituent in position 6 of 3 and 4 is critical. The binding, as well as the fluorescence enhancement, is clearly related to the electron-donating effect of this substituent. Accordingly, compound 4 shows the strongest binding affinity and the strongest fluorescence enhancement. Quantum chemical calculations reveal a general mechanism related to the twisted intramolecular charge transfer (TICT) model. Accordingly, an increase of the twist angle between the phenyl ring in position 6 and the phenanthridinium core opens a nonradiative channel in the excited state that depends on the electron-donating character of the phenyl group. Access to this channel is hindered upon binding to DNA.

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Section: Quantum Chemical Calculationssupporting

confidence: 75%

Optical, Redox, and DNA‐Binding Properties of Phenanthridinium Chromophores: Elucidating the Role of the Phenyl Substituent for Fluorescence Enhancement of Ethidium in the Presence of DNA

Prunkl

Pichlmaier

Winter

et al. 2010

Chemistry A European J

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“…38 Our previous calculations for such biaryls with considerable charge transfer nature (e.g. the dimethylaminophenylpyridinium cation 23 and the betaine B30 18 ) showed that the TDB3LYP calculations are in excellent agreement with other theories (CIS, CASSCF). All these results from different calculational models are consistent with the experimental data (fluorescence quenching and the increase of the fluorescence quantum yield with solvent cooling).…”

Section: Calculationsmentioning

confidence: 73%

“…The model of twisted intramolecular charge transfer TICT applies in a modified way, as reported for dimethylanilino-pyridinium (DPY + ). 20 In this system, the fluorescence is strongly quenched by a viscosity-controlled barrierless twisting motion linked with a near-complete localization of the positive charge on the anilino moiety, indicating the presence of a close-lying S 0 /S 1 conical intersection 20,23 as in the betaines. In contrast, the corresponding neutral TICT compound p-dimethylanilino-benzonitrile is characterized by dual fluorescence from an allowed intramolecular charge transfer ICT state of more planar conformation and a forbidden TICT state with enhanced charge transfer character, reached after conformational relaxation towards the perpendicular geometry.…”

Section: Introductionmentioning

confidence: 85%

“…The aim of this study is to characterize the ESPT and CSh dynamics as a function of the solvent properties and determine whether these processes are concerted or independent. The excited-state dynamics will be particularly discussed by comparison with those previously reported for the zwitterionic OPPy-1 analog 19 on the one hand and for the neighboring DPY + cation 20,23 on the other hand.…”

Section: Introductionmentioning

confidence: 96%

“…Cationic D-A biaryl systems can also display photoinduced ICT coupled to interring twisting motion. [20][21][22][23] The ICT transition corresponds to a charge shift (CSh) process from the neutral to the cationic ring. The model of twisted intramolecular charge transfer TICT applies in a modified way, as reported for dimethylanilino-pyridinium (DPY + ).…”

Section: Introductionmentioning

confidence: 99%

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Excited-state dynamics of phenol–pyridinium biaryl

Malval

Chaumeil

Rettig

et al. 2012

Phys. Chem. Chem. Phys.

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The excited-state dynamics of a donor-acceptor phenol-pyridinium biaryl cation was investigated in various solvents by femtosecond transient absorption spectroscopy and temperature dependent steady-state emission measurements. After excitation to a near-planar Franck-Condon delocalized excited S(1)(DE) state with mesomeric character, three fast relaxation processes are well resolved: solvation, intramolecular rearrangement leading to a twisted charge-shift (CSh) S(1) state with localized character, and excited-state proton transfer (ESPT) to the solvent leading to the phenoxide-pyridinium zwitterion. The proton transfer kinetics depends on the proton accepting character of the solvent whereas the interring torsional kinetics depends on the solvent polarity and viscosity. In nitriles, ESPT does not occur and interring twisting arises with no significant intrinsic barrier, but still slower than solvation. The CSh state is notably fluorescent. In alcohols and water, ESPT is faster than the solvation and DE → CSh relaxation processes and yields the zwitterion hot ground state, which strongly quenches the fluorescence. In THF, solvation and interring twisting occur first, leading to the fully relaxed, weakly fluorescent CSh state, followed by slow ESPT towards the zwitterion. At low temperature (77 K), the large viscous barrier of the solvent inhibits the torsional relaxation but ESPT still arises to some extent. Strong emission from the DE geometry and planar zwitterion is thus observed. Finally, quantum chemical calculations were performed on the ground and excited state of model phenol-pyridinium and phenoxide-pyridinium compounds. Strong S(1) state energy stabilization is predicted upon twisting in both cases, consistent with a fast relaxation towards the perpendicular geometry. A substantial S(0)-S(1) energy gap is still present for the twisted cationic species, which can explain the long-lived emission of the CSh state in nitriles. A quite different situation arises with the zwitterion for which the S(0)-S(1) energy gap predicted at the twisted geometry is very small. This suggests a close-lying conical intersection and can account for the strong fluorescence quenching observed in solvents where the zwitterion is produced by ESPT.

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