Influence of self-quenching of the benzene triplet state on estimates of naphthalene T2→T1 internal conversion rates

Self-quenching of the benzene triplet state is shown to be important under the conditions employed by Ladwig and Liu to estimate the T₂ lifetime of naphthalene derivatives. The appropriate kinetic expressions, which reinforce the validity of their experimental approach, are presented and their data corrected for the self-quenching process. The corrected data indicate a slightly larger deuterium effect and somewhat shorter T₂ lifetimes than previously estimated.     

Qualitative considerations of the T1 → S0 intersystem crossing in benzene

We consider the equivalent of the S₀(¹A_1g → T₁(³B_1u absorption spectrum of benzene obtained by Burland et al. On the basis of this spectrum we suggest that the theoretical rate of the T₁(³B_1u) → S₀(¹A_1g) intersystem crossing in benzene is faster by several orders of magnitude than that obtained in recent theoretical work. Furthermore, it is suggested that the rate of this process is not retarded drastically upon deuteration, as claimed in the literature. A new interpretation of the S_o(¹A_1g) → T₁(³B_1u absorption spectrum is also given.     

Effects of limited CI on T1 → S0 oscillator strength and phosphorescence lifetime of pyrazine

Using modified CNDO/S/CI wavefunctions, the effects of 10, 20, 30 and no CI on the oscillator strength of the T₁ → S_o transition and phosphorescence lifetime of pyrazine was investigated. From these calculations, it was determined that although the individual numbers varied, the order of magnitude remained fairly constant, approximately 10^?2 s. The closest results to the experimental values for oscillator strength and phosphorescence lifetime was obtained with 20 and 30 CI     

A CNDO/S study on the Tn ← T1 absorption spectrum of 1,1′-binaphthyl

CNDO/S calculations demonstrate that changes in the T_n ← T₁ absorption spectrum of 1,1′-binaphthyl in going from rigid to fluid media is consistent with a rotation of the chromophores about the interconnecting bond to a nearly planar trans configuration.     

Deuterium isotope effect in the T1 → S0 radiationless transition of propynal in the gas phase

The phosphorescence lifetimes of propynal-h₁ and propynal-d₁ have been measured at room temperature in the 40 mTorr-1 Torr pressure range The reciprocal of the zero-pressure lifetime (k₀) is (3.10 ± 0.05) × 10³ and (1.70 ± 0.04) × 10³ s^?1 for propynal-h₁ and propynal-d¹ For both compounds the rate constant for self-quenching between triplet and ground-state molecules is k_SQ = (1 2±007) × 10³ Torr^?1 s^?1 The deuterium isotope effect is attributed to the T₁ → S₀ radiationlcss decay, for which k^H_ISC/k^D_ISC = 2 4     

Excited states and photochemistry of saturated molecules. extended basics calculations on the 1B1 (1T2) state of methane

The surface of the lowest excited singlet state in methane is analyzed using a basis set composed of 4-31G augmented by a set of one s and three p Rydbergs. The state (1T₂ in T_d symmetry, 1B₁ in C_2v) is found to be dissociative to 1B₁ CH₂ and ground state H₂. Vertically a Rydberg state, 1B₁ rapidly becomes a valence state on distortions from tetrahedral symmetry. Avoided crossings with higher B₁ states are discussed.     

Infrared linear dichroism of the T1 state of acridine in stretched polyethylene

We report the first determination of the symmetry of an excited-state vibration observed with direct infrared absorption. We assign the excited triplet-state vibration of acridine at 751 cm^?1 to b₁ symmetry.     

Ein Radioimmunoassay zur simultanen Bestimmung von T3 und T4 im Blutserum mit Hilfe kleiner Ionenaustauschers?ulen

Zusammenfassung Eine radioimmunologische Methode zur simultanen Bestimmung der beiden Schilddrüsenhormone T₃ und T₄ im Blutserum wird beschrieben. Die Abtrennung der Hormone von den Serumproteinen, die Reaktion mit dem Antiserum und die bound-free-Trennung erfolgen auf kleinen lonenaustauschersäulen. Als Säulenfüllung dient ein Mischbettaustauscher, bestehend aus QAE- und SP-Sephadex. Die Analysenergebnisse sind mit der G-25 Säulenmethode vergleichbar. Der Materialaufwand bei Einmalsäulen kann durch die Verwendung des beschriebenen Ionenaustauschers stark gesenkt werden.Herrn a.o. Univ.-Prof. Dipl.-Ing. Dr. techn. Wladimir Limontschew zum 60. Geburtstag     

Fluorescence of the antharacenes following Tn → T1 excitation studied by a double excitation method

The fluorescence from the lowest excited singlet state following excitation of the lowest triplet state was observed for anthracene, 9-methylanthracene, and 9-phenylanthracene in ethanol by a newly devised double excitation method which is essentially the combination of flash and laser photolysis. The quantum yield of intersystem crossing from the excited triplet state, T_n(n ? 2), to the lowest excited singlet state was markedly increased by methyl- and phenyl-substitution at the meso-position.     

Distribution and conjugation of the π-electrons in the T1 state of some BNC-heterocycles

For the first time the lowest excited triplet state T₁ of BNC-heterocycles has been investigated. The phosphorescence and ODMR-spectroscopic measurements allow conclusions with respect to the distribution and conjugation of the π-electrons and thus the controversial question of the aromaticity of these compounds. Whereas T₁ in 2-methyl-1,3,2-benzodiazaborolidine may be described by a benzene-like ³B_1u state which is distorted along the ν₈ vibration the decay characteristics of the triplet state of 2-methyl-1,3,2-benzothiazaborolidine is dominated by the local C_2v symmetry around the heavy atom sulfur. In the case of 2-methyl-2-boradihydroperimidine we find a naphthalene-like ³A₁ state for T₁. The zero-field splitting confirms that the electronic triplet excitation is essentially localized in the benzene or naphthalene nucleus and the annellated heterochain participates only little in the π-conjugation.     

Isotope effects on intensities and excitation exchange interactions in the T1 state of crystalline naphthalene

We have observed that the naphthalene-d₈ crystal shows 40% less net Davydov splitting than the naphthalene-h_g crystal. Comparisons of isotope effects on splittings and intensities show vibronic contributions to both spin—orbit and excitation exchange interactions involving totally symmetric modes.     

Interpretation of the optical dephasing time and lineshape function in the S0 → T1 exciton transitions of 1,4-dibromonaphthalene

The lineshape function for the S₀ → T₁ absorption in 1,4-dibromonaphthalene (DBN) is analyzed in terms of exchange theory. It is shown that the dominant optical dephasing mechanism for the electric dipole transition to the k = 0 state in the band results from the absorption and emission of a low energy optic phonon. This process dephases the optical absorption because of frequency differences of the phonon in the ground and excited state. In addition, it is shown how to extract the energy of the phonon responsible for dephasing, the phonon absorption rate, and the lifetime in the phonon promoted state from the data. The analysis of the data for DBN shows that very little dephasing of the optical transition occurs before ≈ 15 K but from 15 K to ≈ 40 K the singlet-triplet transitions to site I (20192 cm^?1) and site II (20245 cm^?1) are dephased by absorption and emission of an ≈ 38 cm^?1 and 45 cm^?1 phonon respectively. The phonon absorption rates by the k = 0 state in the exciton band are similar for both sites being 5 × 10⁶ s^?1 and 3 × 10⁵ s^?1 at 4 K and 7 × 10¹¹ s^?1 and 4 × 10¹¹ s^?1 at 30 K for site I and II respectively. Finally, the lifetimes in the phonon promoted state for sites I and II are 0.23 and 0.28 ps over the range 15–40 K.     

Enantioselective sequential-injection chemiluminescence immunoassays for 3,3′,5-triiodothyronine (T3) and thyroxine (T4)

This study deals with the development of enantioselective flow-through immunosensors for triiodothyronine (T₃) and tetraiodothyronine (thyroxine, T₄) on the basis of a competitive assay using enantioselective antibodies. The instrumental set-up is based on a simple sequential-injection system equipped with a chemiluminescence detector and an immunoreactor, which consists of a flow-cell packed with immobilized haptens. As haptens, 4-amino-l-phenylalanine (4-amino-l-Phe), 4-amino-d-Phe or l-T₃ were used. Antibodies directed against 4-amino-l- or d-Phe or l-T₃ were labeled with an acridinium ester. Three different approaches for immobilizing the haptens were investigated including simple adsorption on polystyrene, chemical binding to an activated methacrylate polymer and binding via the biotin-streptavidin binding (BSB) system. The latter approach showed the best results regarding repeatability and sensivity. Using biotinylated l-T₃ immobilized onto a streptavidin-derivatized trisacryl support and labeled anti-l-T₃ antibodies, a detection limit of 15.5 fmol/ml for l-T₃ was obtained. One assay cycle including regeneration takes only about 5 min. This approach was applied to detect l-T₃ in plasma samples without any sample pre-treatment. The average recovery from spiked plasma sample was about 93% with a R.S.D. below 5%.     

The potential energy curve for the B1IIu state of Li2

Multiconfiguration self-consistent field calculations of the potential curve for the B¹Π_u state of Li₂ show a 700 cm^?1 high hump at 5.365 Å in good agreement with experimental estimates of 930 ± 300 cm^?1 and 523 ± 50 cm^?1.     

Effect of allylic and homoallylic substituents on cross metathesis: syntheses of prostaglandins F2α and J2

We describe the effect of allylic (C15) and homoallylic (C11) substituents on cross metathesis reactions with Corey lactone derivatives. This strategy has led to the successful syntheses of PGF_2α and PGJ₂.     

Franck—condon factors of the T1 ↷ S0 radiative and nonradiative transitions of naphthalene-h8 and -d8-a correlation function analysis

Franck—Condon factors for the T₁ ? S₀ transition in naphthalene-h₈ and naphthalene-d₈ are calculated employing the correlation function approach which allows us to investigate the distribution of the released electronic energy among the normal modes of the Final ground state. The relevant coupling parameters relating to geometry, frequency and anharmonicity changes due to excitation are included. Those related to geometry changes are obtained from the vibronic intensities of the phosphorescence spectrum as well as from a calculation implementing a semi-empirical relation between bond order and bond length. The calculated nonradiative rates compare well with the experimental rates in terms of absolute magnitude and deuterium effect. The semi-empirical calculations of the ribtonic intensities provide detailed information about force fields that are otherwise indistinguishable on the basis of their ability to reproduce infrared frequencies.     

Threshold energies for production of CH2(3B1) and CH2(1A1) from ketene photolysis. The CH2(3B1) ↔ CH2(1A1) energy splitting

By measuring the relative CO quantum yields from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25° for CH₂CO(¹A₁) → CH₂(³B₁) + CO(¹Σ⁺) to be 75.7 ± 1.0 kcal/mole. This corresponds to a value of 90.7 ± 1.0 kcal/mole for ΔH_f298⁰[CH₂(³B₁)]. By measuring the relative ratio of CH₂(¹A₁)/CH₂(³B₁) from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25°C for CH₂CO(¹A₁) → CH₂(¹A₁) + CO(¹Σ⁺) to be 84.0 ± 0.6 kcal/mole. This corresponds to a value of 99.0 ± 0.6 kcal/mole for ΔH_f298⁰[CH₂(¹A₁)]. Thus a value for the CH₂(³B₁) ? CH₂(¹A₁) energy splitting of 8.3 ± 1 kcal/mole is determined, which agrees with three other recent independent experimental estimates and the most recent quantum theoretical calculations.     

Theoretical analysis of vibronic coupling in the lowest T1[3A'2(ππ*)] state of triphenylene-h12 and-d12

The recently observed T₁ ← S_O excitation spectra of triphenylene-h₁₂ and -d₁₂ are analysed in terms of interstate pseudo-Jahn-Teller and intrastate Jahn-Teller coupling of the two lowest triplet states, T₁ [³A'₂(ππ¹)] and T₂[³E'(ππ^*)], via an e' mode.