[3.3]‐ and [4.4](2,7)Pyrenophanes as Excimer Models: Synthesis, Molecular Structure, and Spectroscopic Properties

Abstract

As excimer models the [3.3)-and [4.4)pyrenophanes 1 and 2 were synthesized. As the key precursor for the synthesis of 1 the octahydro-dithia[4.4)pyrenophane 9 was obtained by cyciisation of 4 and 8, the syntheses of which are described. Disulfone 10, derived from 9, on vapour-phase pyrolysis yielded 11 which by dehydrogenation was converted into 1. In an analogous route 2 was obtained via 16, 17, and 18 starting from 4 and IS (prepared in the reaction sequence 12 -13 -14 -IS). -The molecular structures of 1 and 2, determined by X-ray structure analyses, are discussed with regard to transanular distances and deviations from planarity of the pyrene units. The first and most typical example of an 'excimer' formation has been observed for pyrene 1). On photoexcitation a complex is formed by an excited pyrene molecule with a second pyrene which is in the electronic ground state: Ar· + Ar ¢ (Arz)* (excited dimer = 'excimer'). Whereas absorption spectra are not affected, excimer formation results in a concentration dependent change in the fluorescence emission which, as compared to monomer emission, is strongly red-shifted, broad, and structureless. In spite of the undisputed importance of excimers for the photophysics and photochemistry of aromatic systems, so far only very limited experimental evidence has been

Chimerical Pyrene‐Based [7]Helicenes as Twisted Polycondensed Aromatics

“…[32]) or,i mportantly,[ 2.2](2,7)pyrenophane (emission l max = 556 nm in 2-methyltetrahydrofuran), [3.3](2,7)pyrenophane (emission l max = 515 nm in 2-methyltetrahydrofuran) and [4.4](2,7)pyrenophane (emission l max = 469 nm in 2-methyltetrahydrofuran). [33] These [n.n](2,7)pyrenophanes display ac oplanar arrangement of the pyrene subunits, which are in close contact (3.78, 3.48 and 3.48 f or the interplanar distance in the centre of the [2.2], [ 3.3] and [4.4] congeners). Clearly,t he terminal pyrene units in 1 and (M,R,R)-(À)-2 are in ap roper spatiala rrangement( the pyrene units in (M,R,R)-(À)-2 are stacked and closely parallel, as demonstrated by its X-ray crystal structure;s ee above) to allow for the formation of an intramolecular excimer state upon excitation, [34] which is remarkably stabilised.…”

„Protonenschwamm”︁‐Verbindungen und die Geometrie von Wasserstoffbrücken: Aromatische Stickstoffbasen mit ungewöhnlicher Basizität

“…Selbst unter Bedingungen, unter denen an den Stickstoffatomen eine nur dreifache Ethylierung erfolgte (Ethyliodid, Natriumhydrid, 3 h RuckfluB in Tetrahydrofuran), war die 9-Stellung des Fluorens bereits vollstandig ethyliert: In 70% ' Ausbeute war 4-Diethylamino-9,9-diethyl-5-ethylami1iofluoren 11 12.8 +O. Selbst unter Bedingungen, unter denen an den Stickstoffatomen eine nur dreifache Ethylierung erfolgte (Ethyliodid, Natriumhydrid, 3 h RuckfluB in Tetrahydrofuran), war die 9-Stellung des Fluorens bereits vollstandig ethyliert: In 70% ' Ausbeute war 4-Diethylamino-9,9-diethyl-5-ethylami1iofluoren 11 12.8 +O.…”

Intramolecular excimer fluorescence from folded ground state rotamers of N,N'dimethyl-N,N'-dipyrenylurea protophanes

“…Molecules possessing two pyrene chromophores that can adopt sandwich structures display large monomer-excimer spectral shifts. Examples include the 1,3-dipyrenylpropanes (1 and 2) (3-6) and [n.n](2,7)pyrenophanes (n = 2, 3, or 4) (3-5) (7). Conversely, molecules in which only partial overlap of the two pyrenes is possible display either monomer fluorescence or excimer fluorescence with small monomer-excimer spectral shifts.…”