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RISS 인기검색어
- 검색키워드
- 저자 : Higginbotham, Andrew P. (검색결과 3 건)
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Lin, Tze-Chia,Cole, Jacqueline M.,Higginbotham, Andrew P.,Edwards, Alison J.,Piltz, Ross O.,Pé,rez-Moreno, Javier,Seo, Ji-Youn,Lee, Seung-Chul,Clays, Koen,Kwon, O-Pil American Chemical Society 2013 JOURNAL OF PHYSICAL CHEMISTRY C - Vol.117 No.18
<P>The molecular and supramolecular origins of the superior nonlinear optical (NLO) properties observed in the organic phenolic triene material, OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile), are presented. The molecular charge-transfer distribution is topographically mapped, demonstrating that a uniformly delocalized passive electronic medium facilitates the charge-transfer between the phenolic electron donor and the cyano electron acceptors which lie at opposite ends of the molecule. Its ability to act as a “push–pull” π-conjugated molecule is quantified, relative to similar materials, by supporting empirical calculations; these include bond-length alternation and harmonic-oscillator stabilization energy (HOSE) tests. Such tests, together with frontier molecular orbital considerations, reveal that OH1 can exist readily in its aromatic (neutral) or quinoidal (charge-separated) state, thereby overcoming the “nonlinearity-thermal stability trade-off”. The HOSE calculation also reveals a correlation between the quinoidal resonance contribution to the overall structure of OH1 and the UV–vis absorption peak wavelength in the wider family of configurationally locked polyene framework materials. Solid-state tensorial coefficients of the molecular dipole, polarizability, and the first hyperpolarizability for OH1 are derived from the first-, second-, and third-order electronic moments of the experimental charge-density distribution. The overall solid-state molecular dipole moment is compared with those from gas-phase calculations, revealing that crystal field effects are very significant in OH1. The solid-state hyperpolarizability derived from this charge-density study affords good agreement with gas-phase calculations as well as optical measurements based on hyper-Rayleigh scattering (HRS) and electric-field-induced second harmonic (EFISH) generation. This lends support to the further use of charge-density studies to calculate solid-state hyperpolarizability coefficients in other organic NLO materials. Finally, this charge-density study is also employed to provide an advanced classification of hydrogen bonds in OH1, which requires more stringent criteria than those from conventional structure analysis. As a result, only the strongest OH···NC interaction is so classified as a true hydrogen bond. Indeed, it is this electrostatic interaction that influences the molecular charge transfer: the other four, weaker, nonbonded contacts nonetheless affect the crystal packing. Overall, the establishment of these structure–property relationships lays a blueprint for designing further, more NLO efficient, materials in this industrially leading organic family of compounds.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2013/jpccck.2013.117.issue-18/jp400648q/production/images/medium/jp-2013-00648q_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp400648q'>ACS Electronic Supporting Info</A></P>
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Oh, Chan Seok,Pereira, Daniel de Sa,Han, Si Hyun,Park, Hee-Jun,Higginbotham, Heather F.,Monkman, Andrew P.,Lee, Jun Yeob American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.41
<P>This study shows a molecular design strategy for controlling the dihedral angle of two carbazole donors linked to a 2,4-diphenyl-1,3,5-triazine acceptor by a phenyl unit. Using this approach, six thermally activated delayed fluorescence emitters were synthesized with donors placed in various positions around a central phenyl core, and the photophysical relationship between the donor position and its dihedral angle was investigated. We demonstrate that this angle can affect both the strength of the charge transfer state and the conjugation across the entire molecule, effectively changing the singlet-triplet energy gap of the system. We conclude that materials containing two substituted −ortho donors or one −ortho and an adjacent −meta have the smallest energy gaps and the shortest delayed fluorescence lifetimes. On the other hand, emitters with no −ortho substituted donors have larger energy gaps and slow-to-negligible delayed fluorescence. When applying these materials to organic light-emitting diodes, these blue-emitting devices have a range of electrical properties, the best producing efficiencies as high as 21.8% together with high resistance to roll-off that correlate with the reverse intersystem crossing rates obtained.</P> [FIG OMISSION]</BR>
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