Dependence of the Efficiency of Triplet-Triplet Energy Transfer on the Distance Between the Donor and Acceptor

Abstract

The triplet-triplet and singlet-singlet energy transfer is investigated both experimentally and theoretically in the anthracene -Nile red system. Quantum-chemical investigations of the special features in the formation of electronically excited states and photoprocesses in the donor-acceptor pair are performed. It is demonstrated that atypical distance dependence of the efficiency of triplet-triplet energy transfer in the Langmuir-Blodgett multilayered thin films is caused by additional quenching of donor particles due to the process of energy transfer to acceptor centers by the inductive-resonant mechanism.The triplet-triplet (Т-Т) electronic excitation energy transfer discovered by Terenin and Ermolaev [1] in the 50s of the ХХ century is caused by the exchange-resonant interactions between the excited and unexcited molecules spaced at a distance not exceeding several nanometers [2]. Therefore, the efficiency of energy transfer is extremely sensitive to the spacing and mutual orientation of the energy donor and acceptor. Investigations of organic compounds in which the donor and acceptor chromophores were fixed in a rigid insulating chain have demonstrated that the T-T energy transfer is possible only when the spacing does not exceed 1-1.2 nm [2]. However, because of the existence of conformations of molecules in which the donor and acceptor parts are in the van-der-Waals contact, the estimated efficiency of T-T energy transfer as a function of the spacing in such compounds can be not entirely correct [2].To study experimentally the influence of the orientational and distance factors on the efficiency of intermolecular energy transfer, the technology of the Langmuir-Blodgett (LB) films can be used which allows donoracceptor systems to be formed when particle spacing and their mutual orientation are strictly fixed.In [3] the T-T energy transfer between anthracene (donor) and rhodamine C (acceptor) layers was observed by the LB method. Migrating triplet anthracene excitons, leaving the surface layer of anthracene, transferred their energy to dye molecules. Investigations demonstrated that sensitized delayed fluorescence of the acceptor is annihilation in nature. In the subsequent studies, results of experimental investigations of the process of T-T energy transfer between 1.2-benzantracene molecules and amphiphilic analog of rhodamine C [4] and in the anthracene -amphiphilic Nile red pair [5] located in different layers of the LB films were presented. All dyes-acceptors have low quantum yields into the triplet state in the case of direct photoexcitation.In [5,6] it was established that the efficiency of triplet energy transfer from the donor to the acceptor depended on the temperature because of inhomogeneous broadening of triplet levels of the energy donor. The dependence of the donor luminescence quenching on the distance between the donor and acceptor layers demonstrated that the energy was transferred at distances much larger than it followed from the exchange resonant nature of the T-T energy transfer [7].

Singlet Oxygen Generation from Polyaminoglycerol by Spin-Flip-Based Electron Transfer

“…In addition, the energy transfer is strongly dependent on the distance between the donor and the acceptor, rendering the estimation of its efficiency highly challenging due to the mobility of O 2 ( Scheme 1 a). 18 , 19 …”

“…In addition, the energy transfer is strongly dependent on the distance between the donor and the acceptor, rendering the estimation of its efficiency highly challenging due to the mobility of O 2 (Scheme 1a). 18,19 Herein, we report a molecular design strategy for 1 O 2 generation via spin-flip-based electron transfer. This pathway harnesses the nitrogen lone pair−O 2 −hydrogen-bonding interaction to minimize the distance between the photosensitizer and O 2 (Scheme 1b).…”

“…Therefore, strategies based on the utilization of heavy atoms to increase the spin–orbit coupling constant and on intramolecular donor–acceptor charge separation to reduce Δ E S 1 –T n have been explored. − However, photosensitizers based on these principles suffer from dark toxicity, poor solubility, and low stability. In addition, the energy transfer is strongly dependent on the distance between the donor and the acceptor, rendering the estimation of its efficiency highly challenging due to the mobility of O 2 (Scheme a). , …”