Proton phototransfer performance for 2-heteryloxazoles

Druzhinin, S. I.; Troyanovskii, I. V.; Krashakov, S. A.; Uzhinov, B. M.

doi:10.1007/bf01160496

Cited by 2 publications

(2 citation statements)

References 4 publications

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“…3,7 With DMABN in n-hexane at 25 C, the sum of the fluorescence quantum yield F f and the yield of intersystem crossing F ISC is close to unity, 8 showing that internal conversion is not an important decativation pathway of its S 1 state in this solvent at room temperature. Efficient thermally activated internal conversion has, however, been observed with a number of other aromatic amines: 3,5-dimethyl-4-(methylamino)benzonitrile (MHD), 9 1-(dialkylamino)naphthalenes, [10][11][12][13][14][15] a series of 4-substituted 1-(dimethylamino)naphthalenes 15 and 9-(dimethylamino)anthracenes. 16 It has been shown that the occurrence of this internal conversion is governed by the twist angle of the amino group relative to the plane of the aromatic moiety, as well as by the energy gap DE(S 1 ,S 2 ) between the two lowest excited singlet states.…”

Section: Introductionmentioning

confidence: 99%

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

Druzhinin

Jiang

Demeter

et al. 2001

Phys. Chem. Chem. Phys.

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The introduction of a fluoro-substituent in the phenyl ring of 4-(1-azetidinyl)benzonitrile (P4C) leads to smaller fluorescence quantum yields Phi (f) and shorter decay times tau in alkane solvents (cyclopentane, n-hexadecane, n-hexane and 2-methylpentane). In cyclopentane at 25 degreesC, Phi (f) and tau equal 0.02 and 0.14 ns for 2-fluoro-4-(1-azetidinyl)benzonitrile (P4CF2) and 0.11 and 0.85 ns for 3-fluoro-4-(1-azetidinyl)benzonitrile (P4CF3), as compared with 0.27 and 4.55 ns for P4C. The fluorescence originates from a locally excited (LE) state and dual fluorescence due to intramolecular charge transfer is not observed for the three aminobenzonitriles at any temperature in the alkane solvents. By measuring the yields of intersystem crossing Phi (ISC), it follows that this enhancement of the radiationless deactivation of the first excited singlet state S-1 is due to thermally activated internal conversion (IC). The IC yield Phi (IC) in cyclopentane at 25 degreesC, as an example, is considerably larger for P4CF2 (0.93) than for P4CF3 (0.35) and of minor importance for P4C (0.03). The IC activation energies E-IC of P4CF2 (12.6 kJ mol(-1)), P4CF3 (19.3 kJ mol(-1)) and P4C (38.1 kJ mol(-1)) in cyclopentane were determined by fitting tau measured as a function of temperature, together with data for Phi (f) and Phi (ISC). Similar E-IC values were obtained in n-hexane and n-hexadecane. These data show that the increase in IC efficiency from P4C via P4CF3 to P4CF2 is caused by a decrease in E-IC. The radiative rate constants k(f) in cyclopentane of P4CF2 and P4CF3 are about twice that of P4C, probably due to the mixing of the S-2(L-1(a),CT) and S-1(L-1(b)) states of P4C caused by the molecular asymmetry introduced by the F-substituents. It is assumed that the lowering of the IC barriers in P4CF2 and P4CF3 is governed by an F-substituent-dependent difference in the energies of the molecular configuration of the azetidinylbenzonitriles that can be reached in S-1 as compared with those in S-0

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Section: Introductionmentioning

confidence: 99%

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

Druzhinin

Jiang

Demeter

et al. 2001

Phys. Chem. Chem. Phys.

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“…With 1DMAN, a thermally activated internal conversion (IC) takes place, which reduces the fluorescence decay time τ as well as the quantum yield Φ f . − This IC process is especially efficient in nonpolar solvents such as n -alkanes at ambient temperature . As an example, for 1DMAN in n -hexane at 25 °C, a decay time τ of 120 ps and a quantum yield Φ f of 0.01 has been determined .…”

Section: Introductionmentioning

confidence: 99%

Internal Conversion in 1-Aminonaphthalenes. Influence of Amino Twist Angle

et al. 1999

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With the 1-aminonaphthalenes 1N5 and 1DMAN a fast radiationless process occurs in n-hexane, diethyl ether, and acetonitrile, which is shown to be internal conversion (IC). The IC reaction is slower with 1N4 and much less efficient with 1MAN and 1AN. This IC process is thermally activated and slows down with increasing solvent polarity, due to a larger IC activation energy. In the ground state S0, the amino twist angle θ relative to the naphthalene plane increases in the order 1MAN, 1AN, 1N4, 1N5, 1DMAN, as derived from absorption and fluorescence spectra, 1H NMR spectra, ground-state dipole moments, and ab initio calculations. For the five 1-aminonaphthalenes in the equilibrated S1 state, the twist angle and the radiative rate constant have similar values. The different IC efficiences of these molecules are therefore determined by the structural differences (amino twist angle) between S1 and S0. A correlation is found between the IC efficiency in these molecules and the twist angle θ. The IC process to S0 starts from the equilibrated S1 state, which is vibronically coupled with S2 due to a small energy gap ΔE(S1,S2). It is therefore concluded that the extent of vibronic coupling and the magnitude of the twist angle θ are the determining factors in the IC process.

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Proton phototransfer performance for 2-heteryloxazoles

Cited by 2 publications

References 4 publications

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

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

Internal Conversion in 1-Aminonaphthalenes. Influence of Amino Twist Angle

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