book of abstracts - IM2NP

A B S T R A C T S THURSDAY, JULY 1 N A N O S E A 2 0 1 0
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10H40-11H00 Photophysical properties of alternated pyridine-ethylenedioxythiophene
oligomers investigated with TD-DFT: towards light triggered molecular
springs
1 – Introduction
Claudine Katan (FOTON, INSA, CNRS, 20 avenue des buttes de Coësmes, CS70839, F-35708 RENNES
Cedex 9, CPM, Unniversité Rennes 1, CNRS, campus de beaulieu, Case 1003, F-35042 RENNES Cedex).
Claudine.Katan@univ-rennes1.fr
Among the various organic systems designed for their optical and electronic properties, novel chromophores
based on the alternation of electron-poor (pyridyl, A) and electron-rich (ethylenedioxythienyl, D)
heterocycles have recently been shown to lead to dramatic enhancement of their photoluminescent properties
with oligomer elongation [1]. These compounds adopt a coiled structure reminding the self-organized
multiturn helical superstructures of alternating pyridine-pyrimidine oligomers [2]. The perspectives for
photonic devices opened by such synthetic routes deserve better understanding of their structure-property
relations.
2 – Abstract
The aim of this work is to explore ground- and excited-state photophysical properties of such (DA)n
chromophores with state of the art time dependent density functional theory (TD-DFT) approaches.
Geometries are optimized at the HF/6-31G and TD-HF/SV level of theory, respectively while absorption and
fluorescence points are treated at the TD-B3LYP level. Calculated data show good agreement with
experimental X-ray data, transition energies, oscillator strengths and radiative lifetimes. Insight in the nature
of the excited states relevant for absorption and emission is gained thanks to Natural Transition Orbital
analysis. It reveals excited state localization prior to emission on one of the ADA moiety for derivatives with
at least two A cycles. Computer design of 8-member oligomers is also performed. For the closed ring,
calculations predict fluorescence quenching and steric hindrance that may hamper synthesis. The open 8-
member derivative shows significant decrease of its helical pitch after excitation, with inhomogeneous
torsion angles along the oligomer, as a consequence of excited state localization prior to emission.
3 – Conclusion
This suggests a new route towards reversible light triggered nanosprings. Such a route could be even further
extended in the framework of molecular devices thanks to dissymmetrical functionalization which allows
spatial control of emission localization [3] and/or by peripheral substitution [2] of active molecular moeties.
[1] F. Chevalier, M. Charlot, C. Katan, F. Mongin and M. Blanchard-Desce, Chem. Commun., 2009, 692-694
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