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Direct Evidence of Torsional Motion in an Aggregation-Induced Emissive Chromophore (Articolo in rivista)

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Direct Evidence of Torsional Motion in an Aggregation-Induced Emissive Chromophore (Articolo in rivista) (literal)

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T. Virgili, A. Forni, E. Cariati, D. Pasini, C. Botta (2013)
Direct Evidence of Torsional Motion in an Aggregation-Induced Emissive Chromophore
in Journal of physical chemistry. C; American Chemical Society, Washington (Stati Uniti d'America)
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Dipartimento di Fisica, Politecnico di Milano, Istituto di Fotonica e Nanotecnologie (IFN)- CNR, P.zza Leonardo Da Vinci 32, 20132 Milano, Italy; ISTM-CNR, Institute of Molecular Sciences and Technologies of CNR, via Golgi 19, 20133 Milano, Italy; Dipartimento di Chimica dell'Universita? degli Studi di Milano, UdR del INSTM di Milano,via Golgi 19, 20133 Milano, Italy; Department of Chemistry and INSTM Research Unit, University of Pavia, Viale Taramelli, 10-27100 Pavia, Italy; Istituto per lo Studio delle Macromolecole (ISMAC), CNR, Via Bassini 15, 20133 Milano, Italy (literal)

Titolo

Direct Evidence of Torsional Motion in an Aggregation-Induced Emissive Chromophore (literal)

Abstract

The aggregation induced emission (AIE) behavior shown by organic chromophores is very interesting for the development of efficient solid state devices. The restriction of intramolecular rotation is by far the most frequently assumed mechanism to explain this behavior; by blocking or reducing this rotation, upon rigidification of the environment, molecular luminescence is restored. By means of ultrafast pump-probe spectroscopy combined with density functional theory (DFT) and and time-dependent DFT calculations, we show direct evidence of intramolecular rotation in a simple push-pull organic chromophore,4-diethylamino-2 benzylidene malonic acid dimethyl ester, possessing AIE properties. The spectral evolution of the stimulated emission band of the chromophore in the first 45 ps after photoexcitation is fully consistent with the presence of a torsional relaxation toward the equilibrium geometry of the excited state, taking place on time scales that depend on the solvent viscosity. The structural features of the excited state fully account for the different photoluminescence efficiencies observed in solvents with different viscosities. (literal)

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