1. Lifetime shortening and fast energy-tansfer processes upon dimerization of a A-π-D-π-A molecule
- Author
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Camilla Ferrante, Norberto Manfredi, Elisabetta Collini, Luca Bolzonello, Mirco Zerbetto, Alessandro Abbotto, Collini, E, Bolzonello, L, Zerbetto, M, Ferrante, C, Manfredi, N, and Abbotto, A
- Subjects
Dimer ,Analytical chemistry ,transient absorption ,02 engineering and technology ,010402 general chemistry ,Excimer ,01 natural sciences ,Molecular physics ,Spectral line ,chemistry.chemical_compound ,Ultrafast laser spectroscopy ,Physical and Theoretical Chemistry ,molecuar dymer ,energy transfer ,Relaxation (NMR) ,Rotational diffusion ,021001 nanoscience & nanotechnology ,Atomic and Molecular Physics, and Optics ,0104 chemical sciences ,Dark state ,chemistry ,fluorescence ,0210 nano-technology ,Ground state ,molecular materials, organic materials - Abstract
Time-resolved fluorescence and transient absorption experiments uncover a distinct change in the relaxation dynamics of the homo-dimer formed by two 2,5-bis[1-(4-N-methylpyridinium)ethen-2-yl)]-N-methylpyrrole ditriflate (M) units linked by a short alkyl chain when compared to that of the monomer M. Fluorescence decay traces reveal characteristic decay times of 1.1 ns and 210 ps for M and the dimer, respectively. Transient absorption spectra in the spectral range of 425-1050 nm display similar spectral features for both systems, but strongly differ in the characteristic relaxation times gathered from a global fit of the experimental data. To rationalize the data we propose that after excitation of the dimer the energy localizes on one M branch and then decays to a dark state, peculiar only of the dimer. This dark state relaxes to the ground state within 210 ps through non-radiative relaxation. The nature of the dark state is discussed in relation to different possible photophysical processes such as excimer formation and charge transfer between the two M units. Anisotropy decay traces of the probe-beam differential transmittance of M and the dimer fall on complete different time scales as well. The anisotropy decay for M is satisfactorily ascribed to rotational diffusion in DMSO, whereas for the dimer it occurs on a faster time scale and is likely caused by energy-transfer processes between the two monomer M units. A dark mistery: Time-resolved experiments reveal a distinct change in the decay dynamic of an A-π-D-π-A molecule upon formation of a covalently linked non-conjugated dimer. The faster decay observed in the dimer is attributed to a dark state, which is presumably associated with charge delocalization between the two multipolar units
- Published
- 2013