Photophysical Properties of Coplanar and Twisted 1,4-Bis(9-ethynylanthracenyl)benzene. Rotational Equilibration in the Excited States of Diaryalkynes

Abstract

We report the synthesis and photophysical properties of 1,4-bis(9-ethynylanthracenyl)benzene. Results in dilute hexane solutions give a very high fluorescence quantum yield (Φ ) 0.97) and a lifetime of τ ) 1.8 ns. Studies at different temperatures, viscosities, and micromorphologies, as well as excited-state semiempirical calculations, indicate that conformations having aryl groups coplanar absorb and emit at wavelengths that are longer than those that have their aryl groups orthogonal or twisted. A simple MO picture is consistent with essentially frictionless aryl group rotation in the ground state and a relatively high rotational barrier in cummulene-like excited states.

Experimental and theoretical studies of spectroscopic properties of simple symmetrically substituted diphenylbuta-1,3-diyne derivatives

“…The higher energy barrier of rotation in the excited state than in the ground state is attributed to breaking of the cylindrical structure of the electron density along the axis of symmetry 58 and the adoption of the partial cummulene-like structure. 54 The calculated lengths of single and triple bonds with that of the crystal structure are gathered in Table 4 ESI. † The bond lengths of the buta-1,3diyne unit obtained for the optimized structure using quantum chemical calculations are slightly longer than that of the crystal structure.…”

Twists and turns: Studies of the complexes and properties of bimetallic complexes featuring phenylene ethynylene and related bridging ligands

“…These complementary areas of investigation (conductance studies of metal|molecule|metal junctions and intramolecular charge transfer studies in {L x M n }(-bridge){M n L x } systems) are both driven by the extended -conjugated backbone of BPEB. The extent of delocalisation is highly sensitive to the molecular conformation, with planar conformations offering more extended delocalisation pathways along the long molecular axis [72][73][74]. An analysis of the torsional motions of the parent molecule, 1,4-bis(phenylethynyl)benzene and the central-ring deuterated derivative 1,4-bis(phenylenethynyl-2,3,5,6-tetradeuteriobenzene, using cavity ringdown spectroscopy revealed a low barrier to rotation of the phenyl(ene) rings in BPEB around the alkynyl linkers (2.7 kcal mol -1 ) [75], a value consistent with earlier estimates [76][77][78][79].…”

Bridged Tolanes: A Twisted Tale

“…Spectra of other tethered tolanes are not shown but similar (see Supporting Information). Both absorption and emission spectra of the planar phanes (5,7,8) are well resolved.…”