Excimer Formation In Crystals Research Articles

Crystal structure and luminescence properties of 4-(4-benzoyloxy-2-hydroxyphenyl)-2,2-difluoro-6-phenyl-1,3,2-dioxaborine

The crystal structure of 4-(4-benzoyloxy-2-hydroxyphenyl)-2,2-difluoro-6-phenyl-1,3,2-dioxaborine (1) was determined by X-ray diffraction analysis. π-π-Stacking interaction between the molecules results in joining the molecules into a three-dimensional layered framework. Luminescence of the aggregates is observed in concentrated solutions of compound 1. Two routes of excimer formation in crystal were revealed by steady-state and time-resolved luminescence spectroscopy: via excitation of single molecules and via excitation of aggregates.

Control of the CT interaction between electron-donor and -acceptor moieties of a 1,4-dicyanonaphthalene–arene dyad for intermolecular exciplex or excimer formation in crystals

Colorless crystals of 1,4-dicyano-2-(4′-methoxybenzyloxy)methylnaphthalene ( 2), which is a 1,4-dicyano-2-methylnaphthalene (DCMN)–4-methylanisole (MA) dyad linked by an ether unit, selectively form a fluorescent intermolecular DCMN–MA exciplex (greenish blue, λ f exciplex = 456 nm ). In contrast, 1,4-dicyano-2-(4′-methylbenzyloxy)methylnaphthalene ( 3), which is a DCMN– p-xylene dyad, forms a fluorescent intermolecular DCMN–DCMN excimer in the crystalline state (blue, λ f excimer = 404 nm ). These findings demonstrate that a moderate charge transfer interaction takes place between the DCMN moiety of 2 and MA moieties of the adjacent molecules of 2, which successfully facilitates the preparation of light-emissive organic crystals.

The hierarchical mode construct: A dynamical approach to photodimerisation and excimer formation in crystals

A mechanism for the localisation of electronic excitation within a pair of molecules in a crystal is described. The key feature is the hierarchical mode construct which enables the time evolution of lattice distortion to be expressed in terms of progressively larger clusters.

Exciton-induced lattice distortion and excimer formation

The considerations necessary for the development of a complete theory of excimer formation in crystals are analysed. A simple model which incorporates exciton-generated lattice distortion into the travelling exciton is presented, a distortion type related to excimer formation defined and the role it plays in establishing a route for excimer formation discussed. The consequences of a large change in pair molecule separation in going from crystal to excimer are emphasised and possible competition with photodimerization as an alternative end result mentioned. Referring to experimental evidence for a travelling excimer in 9-cyanoanthracene, it is shown here that a strong exciton-phonon coupling term peculiar to this crystal would be favourable. Mechanisms suggested elsewhere for migration of excimer excitation in pyrene are discussed in terms of the ideas developed here.