Intramolecular Energy Transfer Mechanism Research Articles

Energy transfer processes in two different bifluorophoric laser dyes

The mechanism of intramolecular energy transfer in two bifluorophoric laser dyes has been investigated by measurements of laser parameters, excited state absorption and phosphorescence spectra. The new value found for the dimethyl-POPOP triplet energy (48.0 kcal/mole) accounts for the different behaviour of the two classes of bifluorophoric dyes used in this investigation.

Photolysis of ethyl α-chlorophenylacetate in cyclohexane

Of many possible primary processes of photolysis of the compouds containing a carboxyl group, the primary reaction of ethyl α-chlorophenylacetate (I) proceeds outside the carboxyl group and is in practice limited only to a homolytic CCl bond rupture. Because of large differences in the rate of hydrogen abstraction by the PhĊHCOOEt and Cl radicals, the main photolysis product of I in cyclo-hexane is PhCH(C 6H 11)COOEt (II) and not PhCH 2COOEt (III) (as it was in the case of α-haloesters). Besides HCl and II, the other products of photolysis of I in cyclohexane are: III, C 6H 11Cl (IV), diethyl α,α-diphenylsuccinate (PhCHCOOEt) 2 (V), traces of p-ClC 6H 4CH 2COOEt (VI), as well as a number of secondary products, of which PhC(C 6H 11) 2COOEt (VII) was identified. The quantum yields of main photolysis products are determined. The Norrish type II reaction does not play any significant role in the photolysis of I. The excited singlet state of I is probably responsible for the CCl bond homolysis. The lifetime of this state has been estimated to be less than or equal to 1 × 10 −11 s, and the quantum yield of fluorescence of I as < 1 × 10 −5. The photolysis of I is sensitized by benzene, and the products and quantum yields of sensitized photolysis are the same as in direct photolysis. The energy transfer takes place from the singlet state of benzene to the ester with the rate constant 7.0 × 10 10 M −1 s −1. The mechanism of intramolecular energy transfer in I is considered.

Influence of cysteamine on intramolecular energy transfer in 5-bromouracil-substituted phage-DNA.

SummaryWith the aid of an analytical ultracentrifuge, single- and double-strand breakage rates of 5-bromouracil (BrU)-substituted DNA of a defective B. subtilis phage (PBSH) were determined after irradiation with U.V. (302, 313 nm) in the presence and absence of cysteamine. The presence of cysteamine reduced the appearance of single-strand breaks (10 per cent) in the BrU-containing strands of hybrid and bifilarly-substituted DNA. The primary breaks lead to secondary breaks in the complementary thymine-containing strand of hybrid DNA or in the complementary BrU-containing strand of bifilarly-substituted DNA (intra-molecular energy transfer). Cysteamine strongly reduces (< 1 per cent) these secondary breaks, indicating that radical reactions are involved in the mechanism of intramolecular energy transfer.

Relations between Intramolecular Energy Transfer Efficiencies and Triplet State Energies in Rare Earth β-diketone Chelates

Abstract The fluorescence yield of europium chelates in several solutions varies, through its maximum value, with the increase in the energy difference between the triplet state of a ligand and the emitting level of an europium ion. The time-resolved spectroscopic measurements show that the excitation energy is transferred from the triplet state to the lower and nearest resonance level of the europium ion. The intramolecular energy transfer mechanisms for europium chelates and terbium chelates are proposed, taking the resonance exchange interaction and the thermal deactivation processes from the emitting levels of rare earth ions into consideration. Steady-state rate equations are made, and the equation of the fluorescence yield is obtained. Thus, the relations between the fluorescence yield and the triplet state energy are estimated and the fluorescence properties of rare earth β-diketone chelates may be qualitatively described.

Mechanism of Intramolecular Energy Transfer in Rare Earth Chelates as Revealed by Infrared Absorption Measurements

Abstract The purpose of this paper is to clarify the mechanism of intramolecular energy transfer from the triplet state of the ligand to the excited levels of the central ion in rare earth chelates. As to seven kinds of samarium β-diketonates, the frequency of infrared absorption due to the stretching vibration of the chelate bond, \ ildeνMO, and the manner of energy transfer are investigated. The probability of energy transfer is estimated from the ratio of the intensity of the samarium emission to that of the ligand phosphorescence, ISm⁄IPh. The overlap integral, S, between the ligand phosphorescence spectrum and the samarium absorption spectrum is obtained. It was found that a linear relation roughly holds between log{(ISm⁄IPh)⁄S} and \ ildeνMO. On the basis of this fact, one is led, by making some arguments, to the conclusion that intramolecular energy transfer is dominated by the resonance mechanism due to the exchange interaction of the π electron system of the ligand triplet state with the f electron system of the central rare earth ion.