Twisted molecular geometry and localized electronic structure of the triplet excited gem-diphenyltrimethylenemethane biradical: substituent effects on thermoluminescence and related theoretical calculations

Substituent effects on the energies of electronic transitions (ETs) between the triplet excited and ground states of gem-diphenyltrimethylenemethane biradicals ( 3 2a ) were explored by using thermoluminescence (TL) spectroscopy and density functional theory (DFT) including time-dependent (TD) DFT....

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Bibliographic Details
Published in:Tetrahedron 2011-09, Vol.67 (38), p.7431-7439
Main Authors: Matsui, Yasunori, Namai, Hayato, Akimoto, Ikuko, Kan’no, Ken-ichi, Mizuno, Kazuhiko, Ikeda, Hiroshi
Format: Article
Language:English
Subjects:
Charge
Charge recombination
Chemistry
Constants
Electron transfer
Electronic structure
Electronics
Exact sciences and technology
Free radicals chemistry
Hammett equation
Kinetics and mechanisms
Mathematical analysis
Molecular geometry
Organic chemistry
Radicals
Reactivity and mechanisms
Slopes
Thermoluminescence
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Summary:Substituent effects on the energies of electronic transitions (ETs) between the triplet excited and ground states of gem-diphenyltrimethylenemethane biradicals ( 3 2a ) were explored by using thermoluminescence (TL) spectroscopy and density functional theory (DFT) including time-dependent (TD) DFT. Linear free energy (Hammett) analyses of TL energies of a variety of para-substituted aryl derivatives of 3 2 * gave reasonable correlations with the substituent constant, σ . The slope of Hammett plots of the data are nearly identical to one obtained from a similar analysis of the photoluminescence (PL) energies of the structurally-related 1,1-diarylethyl radicals ( 3 *). The results suggest that TL of 3 2 * and PL of 3 * derive from a common diarylmethyl radical fluorophore. This interpretation is also supported by the DFT and TDDFT calculated electronic structures and ET energies of 3 2 and 3 . Thermodynamic and kinetic analyses of the charge recombination (CR) process between 2 + and 1 −, which generates 3 2 *, revealed that substituents not only alter the TL energies but also the TL intensities of 3 2 *. The observations made in this effort demonstrate that 3 2 * as well as 3 2 and 2 + have greatly twisted molecular geometries and highly localized electronic structures. [Display omitted]
ISSN:0040-4020
1464-5416
DOI:10.1016/j.tet.2011.06.052