The fluorescence properties of crystalline anthracenes and their dependence on the crystal structures

Abstract

The fluorescence properties of a number of crystalline anthracenes are described. It is found that in excimer-emitting crystals the energy of the emission is shifted by change in temperature much more strongly in infinite-stack structures than in structures based on pair-wise packing. A theoretical treatment is given of the general problem of the excimer emission from a crystal, and is applied to the anthracenes. This theory shows that the sensitivity to temperature for high temperatures is determined by the ratio of the frequencies of intra-pair vibrations in ground and excited states of the particular material. An interpretation of the difference in this ratio for stack and pair structures is given, and some predictions based on this interpretation are given and tested. It is confirmed that structures in which molecular overlap is small give rise to monomer emission.Es werden die Fluoreszenzeigenschaften einer Anzahl Anthrazenkristalle beschrieben. E s wurde gefunden, da13 in ,,excimer"-emittierenden Kristallen die Emissionsenergie durch Temperaturveranderung in unendlich gestapelten Strukturen vie1 starker verschoben ist als in Strukturen, die auf der paarweisen Stapelung beruhen. Es wird eine theoretische Behandlung des allgemeinen Problems der Excimer-Emission von einem Kristall angegeben und auf Anthrazen angewendet. Diese Theorie zeigt, da13 die Temperaturempfindlichkeit fur hohe Temperaturen durch das Verhaltnis der Intra-Pam-Schwingungen im Grundzustand und den angeregten Zustanden des betreffenden Materials bestimmt wird. Es wird eine Interpretation des Unterschieds in diesem Verhaltnis fur Stapel-und Paar-Strakturen gegeben und es nerden einige Vorhersagen auf der Grundlage dieser Interpretation gemacht und gepruft. Es wird bestatigt, da13 Strukturen, in denen die Molekuluberlappung klein ist, RnlaB zu monomerer Emission geben.

Spectroscopy and Photophysics of Monoazaphenanthrenes III. Luminescence of Phenanthridine and 7,8-benzoquinoline in Crystalline State

“…In the case of mentioned just above acridine, in the crystal structure of acridine II and acridine III, two, among its five identified and structurally characterized crystalline modifications [26,27], molecules are arranged in parallel pairs, which provides conditions necessary for occurrence of excimers and excimer fluorescence in crystalline state [28,29]. Namely, in acridine II (monoclinic, with 8 molecules in the unit cell and the space group P 2 1 /a) with two molecules per asymmetric unit, an arrangement of molecules is quite complex.…”

(−)-2-Bornyl 3-(9-anthryl)propionate

“…It was shown that the temperature shift is related to a parameter y, a function of the ratio of norm,-.l-mode frequencies of pairs of molecules in their ground and excited states. For a series of anthracene derivatives Cohen et al (1975) found that the experimental data fitted well when y was ~ 1 for pair structures and when y was ~ 3 for stack structures. This means that the ratio of ground-state to excited-state frequencies is higher for pair than for stack structures.…”

“…The solution behaviour of the excimer fluorescence is, however, normal (Rosseinsky, Hann & Brunner, 1976). After the nomenclature of Stevens (1962) anthracene derivatives have been classified (Cohen, Ludmer & Yakhot, 1975) into type A, which show monomer fluorescence, and types B~ and B 2, which show excimer fluorescence. In type B~ the anthracene moieties are arranged in infinite stacks with their side groups superimposed; in type B 2 the anthracene moieties are paired with the side groups opposed.…”

“…In type B~ the anthracene moieties are arranged in infinite stacks with their side groups superimposed; in type B 2 the anthracene moieties are paired with the side groups opposed. Cohen et al (1975) have shown that the emission bands of stack structures (B 1) are more sensitive to changes in temperature than those in pair structures (B2). It was shown that the temperature shift is related to a parameter y, a function of the ratio of norm,-.l-mode frequencies of pairs of molecules in their ground and excited states.…”

Solid-state optical properties of the methyl-exopyridine–anthracene rotaxane

“…These works have been led on a wide range of supermolecules, mostly in the liquid phase and in crystalline structures, and the reasons for the emission of a broad red-shifted unstructured PL spectrum have been explained in various ways, depending on the molecular con®guration and on the environment of the optically active entities. Intermolecular interactions like sandwich dimers [6] and excimers [7,8], through-space and throughbond electron transfer [9] and interactions with the solvent [10] can give rise to a dual¯uorescence eect where the observed additional spectral feature is a broad unstructured red-shifted band. In particular, charge separation has been evidenced in D±A compounds, where both the active groups are included in the same supermolecule and separated by a spacer.…”