Sensitized Room-Temperature Phosphorescence of Phenanthrene in the Phenanthrene–β-Cyclodextrin–4'-tert-Butylacetophenone Complex

Abstract Sensitized room-temperature phosphorescence of phenanthrene (P) with a lifetime of 2.49 s has been obtained in the P complex with β-cyclodextrin (βCD) and tert-butylacetophenone (tBA) via triplet–triplet (TT) energy transfer from the tBA donor to the P acceptor upon excitation by a light-emitting diode with an emission maximum at 336 nm. The presence of contact between P and the C=O donor group of tBA inside the βCD cavity was hypothesized based on analysis of the vibrational structure of the fluorescence spectra of the P–βCD–tBA complex. Quantum chemical DFT calculations demonstrate that excitation of the C=O group and subsequent TT transfer in the P∙tBA contact π-complex inside the βCD cavity of the P–βCD–tBA complex lead to a triplet state of the P molecule, which phosphoresces.