Distance Dependence of Triplet Energy Transfer in Water and Organic Solvents: A QM/MD Study

The possibility to optimize optoelectronic devices, such as organic light-emitting diodes or solar cells, by exploiting the special characteristics of triplet electronic states and their migration ability is attracting increased attention. In this study, we analyze how an intervening solvent modifies the distance dependence of triplet electronic energy transfer (TEET) processes by combining molecular dynamics simulations with quantum chemical calculations of the transfer matrix elements using the Fragment Excitation Difference (FED) method. We determine the β parameter characterizing the exponential distance decay of TEET rates in a stacked perylene dimer in water, chloroform, and benzene solutions. Our results indicate that the solvent dependence of β (β vacuum = 5.14 Å -1 > β water = 3.77 Å -1 > β chloroform = 3.61 Å -1 > β benzene = 3.44 Å -1) can be rationalized adopting the McConnell model of superexchange, where smaller triplet energy differences between the donor and the solvent lead to smaller β constants. We also estimate the decay of hole transfer (HT) and excess electron transfer (EET) processes in the system using the Fragment Charge Difference (FCD) method and find that β TEET can be reasonably well approximated by the sum of β EET and β HT constants C.C. acknowledges support from the Spanish Ministry of Economy and Competitivity through the Ramon y Cajal program (ref. RYC-2011-08918). A.A.V. acknowledges financial support from MICINN (Ministry of Science and Innovation, Spain) and the FEDER fund (European Fund for Regional Development) provided by grants CTQ2011-26573, UNGI08-4E-003, and UNGI10-4E-801