Crystal Structure of Supramolecular Naphthalene Dimer Complex within -Cyclodextrin Dimer Emitting Excimer Fluorescence: Molecular-Dynamic Simulation and Quantum Chemical Calculations

The method of molecular dynamics is used to simulate the crystal structure of a supramolecular host-guest system consisting of a beta-cyclodextrin dimer (host) and a stacking naphthalene dimer (guest), emitting excimer fluorescence. A new technique is applied, which consists in replacing guest molecules in a real crystal system, built from beta-cyclodextrin dimers, with a naphthalene dimer. Due to the strength of the natural crystalline cyclodextrin framework, the obtained structure turned out to be stable, which allowed to explain the observed luminescence properties of naphthalene in precipitates of microcrystals of unknown structure using quantum-chemical calculations within the TDDFT method. Calculations showed also that dimer beta-cyclodextrin basket, in which the naphthalene dimer is located, plays the role of space limiter, not allowing weakly bound components to dissociate. A planar parallel orientation is maintained between naphthalene molecules, which preorganizes the system to excimer fluorescence.