Internal conversion with 4-(azetidinyl)benzonitriles in alkane solvents. Influence of fluoro substitution

Druzhinin, Sergey I.; Jiang, Yun‐Bao; Demeter, Attila; Zachariasse, Klaas A.

doi:10.1039/b106171m

Cited by 13 publications

(35 citation statements)

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“…The ICT and LE yields for the ABNs, in n-hexane as well as in MeCN, are considerably larger than F'(ICT) and F(LE) of the XABN4Fs, see Table 2. [6,24,43] With DMABN in MeCN, for example, F'(ICT) is more than 50 times larger than with DMABN4F in this solvent.…”

Section: Fluorescence Quantum Yields F'(ict)mentioning

confidence: 94%

“…As a consequence, the reciprocal of the shortest decay time t 2 is approximately equal to the LE!ICT rate constant k a (Scheme 1), see Equation (10). Although the apparent times t 2 obtained from the global analysis of the LE and ICT decays in Figures 6 and 7 are definitely too short (0.5-1.0 ps, i.e., the LE decay is hardly different from the excitation pulse) to be by themselves meaningful in the SPC experiments, [6,24,31] the absence of an LE decay time longer than 1 ps is of importance in the analysis of the LE and ICT femtosecond transient absorption measurements of the XABN4Fs in the following section.…”

Section: Le Picosecond Decays In N-hexane and Mecnmentioning

confidence: 99%

“…Such an enhancement of IC in 4-aminobenzonitriles by F-substitution has already been reported. [24] The presence of the F-substituents may increase the accessibility of a molecular structure for the ICT state of the XABN4Fs that leads by a conical intersection directly to the ground state, possibly by an increased flexibility of the tetrafluoro-benzonitrile moiety. [44,45] From the ISC and fluorescence yields (Table 2), the internal conversion yields can be determined by using Equation (4).…”

Section: T-t Absorptionmentioning

confidence: 99%

“…[23] First examples of F-substituted aminobenzonitriles in the literature are the two fluoro-N-(azetidinyl)-benzonitriles, for which enhanced thermally activated internal conversion (IC) has been observed in alkane solvents. [24] In the present paper, photostationary spectra and time-resolved picosecond fluorescence and femtosecond transient absorption experiments are reported for five 2,3,5,6-tetrafluoro-aminobenzonitriles XABN4F with different amino groups: dimethyl-amino (DMABN4F), diethyl-amino (DEABN4F), azetidinyl (AZABN4F), methyl-amino (MABN4F) and amino (ABN4F).…”

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confidence: 99%

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Ultrafast Intramolecular Charge Transfer and Internal Conversion with Tetrafluoro‐aminobenzonitriles

et al. 2005

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The five 2,3,5,6-tetrafluoro-4-aminobenzonitriles XABN4F with a dimethyl-amino (DMABN4F), diethyl-amino (DEABN4F), azetidinyl (AZABN4F), methyl-amino (MABN4F) or amino (ABN4F) group undergo ultrafast intramolecular charge transfer (ICT) at room temperature, in the polar solvent acetonitrile (MeCN) as well as in the nonpolar n-hexane. ICT also takes place with the corresponding non-fluorinated aminobenzonitriles DMABN, DEABN and AZABN in MeCN, whereas for these molecules in n-hexane only minor (DMABN, DEABN) or no (AZABN) ICT fluorescence is detected. For the secondary (MABN) and primary (ABN) amines, an ICT reaction does not occur, which makes ABN4F the first electron donor/acceptor molecule with an NH(2) group for which ICT is observed. The ICT state of the XABN4Fs has a dipole moment of around 14 D, clearly smaller than that of DMABN (17 D). This difference is attributed to the electron withdrawing from the CN group to the phenyl ring, exerted by the four F-substituents. The reaction from the initially prepared locally excited (LE) to the ICT state in n-hexane proceeds in the sub-picosecond time range: 0.35 ps (DMABN4F), 0.29 ps (DEABN4F) and 0.13 ps (AZABN4F), as determined from femtosecond transient absorption measurements. In the highly polar solvent MeCN, an ICT reaction time of around 90 fs is observed for all five XABN4Fs, irrespective of the nature of their amino group. This shows that with these molecules in MeCN the ICT reaction rate is limited by the solvent dielectric relaxation time of MeCN, for which a value of around 90 fs has been reported. It is therefore concluded that, during this ultrashort ICT reaction, a large-amplitude motion such as a full 90 degrees twist of the amino group is unlikely to occur in the XABN4Fs. The ICT state of the XABN4Fs is strongly quenched via internal conversion (IC), with a lifetime tau'(0) (ICT) down to 3 ps, possibly by a reaction passing through a conical intersection made accessible due to a deformation of the phenyl group by out-of-plane motions induced by vibronic coupling between low-lying pisigma* and pipi* states in the XABN4Fs.

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Section: Fluorescence Quantum Yields F'(ict)mentioning

confidence: 94%

Section: Le Picosecond Decays In N-hexane and Mecnmentioning

confidence: 99%

Section: T-t Absorptionmentioning

confidence: 99%

mentioning

confidence: 99%

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Ultrafast Intramolecular Charge Transfer and Internal Conversion with Tetrafluoro‐aminobenzonitriles

et al. 2005

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“…The photophysical and photochemical properties of fluorenone (FN) and its derivatives have recently attracted considerable attention because they are excellent model compounds for investigating the molecular structures in both the ground state and electronic excited states, microscopic solvation dynamics and the ultrafast radiationless deactivation mechanism for photoexcited molecules [70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85]. To identify the nature of the electronic excited states of chromophores, several criteria such as absorption intensity, transition energy shift with increasing solvent polarity, direction of transition moment, vibrational structures, fluorescence and phosphorescence lifetime and quantum yields, singlet-triplet splitting, heavy atom effect on the S 0 !…”

Section: Introductionmentioning

confidence: 99%

Insight from Singlet into Triplet Excited‐State Hydrogen Bonding Dynamics in Solution

Zhao

Han

2010

Hydrogen Bonding and Transfer in the Excited State

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IntroductionSolute-solvent interactions play a fundamental role in the photochemistry of organic and biological chromophores in solution [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. In addition to non-specific dielectric interactions between solute and solvent, site-specific intermolecular hydrogen bonding interaction between hydrogen donor and acceptor molecules is another important type of solute-solvent interaction and is central to the understanding of the microscopic structure and function in many molecular systems [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Moreover, the dynamical behaviour of intermolecular hydrogen bonds in electronic excited states plays an important role in determining the rates of many chemical, physical and biochemical processes that occur in hydrogen-bonded surroundings [30][31][32][33][34][35]. Therefore, investigation of the hydrogen bonding dynamics of photoexcited chromophores in hydrogenbonded surroundings is very valuable and helpful in understanding the interesting photophysical and photochemical behaviours of these chromophores, as well as in designing and synthesizing organic functional materials by using hydrogen bonding interactions [36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51].In previous studies we have theoretically investigated the electronic-excited-state structures and dynamics of hydrogen bonding for a variety of organic and biological chromophores, such as coumarin, fluorenone, oxazine, thioketones, novel DÀ ÀpÀ ÀA systems, dihydrogen-bonded phenol-BTMA, protochlorophyllide a, etc. [52][53][54][55][56][57][58][59]. The ground state and electronic excited states were investigated using the density functional theory (DFT) and the time-dependent density functional theory (TDDFT) methods respectively. It has been theoretically demonstrated for the first time that the intermolecular hydrogen bonds formed between these chromophores and the solvents can be significantly strengthened or weakened in the electronic excited states of

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Quenching of fluorescence for fluoro derivatives of the laser dye DCM in polar solutions

et al. 2006

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propanol at room temperature and at 77 K. The fluorescence quantum yield Φ fl of the laser dye DCM increases linearly as the polarity of the binary solvent mixture (toluene+DMSO) increases, from 0.08 in toluene to 0.80 in DMSO. The dependence of Φ fl on the polarity of the mixture toluene+DMSO for DCMF3 and DCMF7 reaches a maximum for a small amount (~2 vol.%) of added polar DMSO; and with further increase in the DMSO concentration (≥50 vol.%), the fluorescence of the fluoro derivatives of DCM is practically completely quenched. The quantum yield for intersystem crossing Φ ST for DCM, DCMF3, and DCMF7 is no greater than 0.01 in solutions of different polarities. We discuss the mechanisms for nonradiative deactivation of the electronic excitation energy for the fluoro derivatives compared with DCM.Key words: laser dye, charge transfer, fluorescence quantum yield, solvent polarity.Introduction. The photophysical properties of organic compounds with electron-donor and electron-acceptor substituents have been widely studied recently [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. They are of interest in connection with their possible application as organic light-emitting diodes in color graphical displays [6], fluorescent labels and visualizing agents in biological systems [7,8], and also owing to their nonlinear optical properties [9, 10] (high quadratic polarizability β). Electron donor/acceptor compounds with effective intramolecular charge transfer are characterized by a large dipole moment in the ground state (µ g ), which generally increases during transition of the molecule to the S 1 state (µ e ), and consequently their photophysical and photochemical properties are determined to a significant extent by the solvent polarity [11].Deactivation of the energy of the excited states of stilbene dyes depends considerably on the polarity and viscosity (stiffness) of the medium. In nonpolar alkane solvents, the absorption and fluorescence spectra of electron donor/acceptor stilbene derivatives have vibronic structure, pronounced mirror symmetry, and a small Stokes shift [12]. The geometry of the molecules in the ground state and the excited state is planar in this case, and emission occurs from a high-lying, locally excited state [13]. Compounds in which rotation of molecular moieties about single and double bonds is possible in nonpolar solvents generally have low fluorescence quantum yield Φ fl [14], and quenching is due to adiabatic transitions to a low-lying non-fluorescent "phantom" state "twisted" about the double bond [13,14]. For model compounds in which internal rotation about the double bond is chemically ruled out [14,15] and for "rigid" coumarin dyes [16-18], a high fluorescence quantum yield has been observed (Φ fl ≥ 0.5) in nonpolar solvents. Φ fl also markedly increases as the viscosity of the nonpolar medium increases, as a result of hindrance of the internal

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Internal conversion with 4-(azetidinyl)benzonitriles in alkane solvents. Influence of fluoro substitution

Cited by 13 publications

References 30 publications

Ultrafast Intramolecular Charge Transfer and Internal Conversion with Tetrafluoro‐aminobenzonitriles

Ultrafast Intramolecular Charge Transfer and Internal Conversion with Tetrafluoro‐aminobenzonitriles

Insight from Singlet into Triplet Excited‐State Hydrogen Bonding Dynamics in Solution

Quenching of fluorescence for fluoro derivatives of the laser dye DCM in polar solutions

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