s0 emission - school of chemistry and...
TRANSCRIPT
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g) characteristics of the S0 → S1 absorption and S1 → S0 emission
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geometry relaxation in S1 of PPV5
AM1/CI
in very long oligomers: S1 geometry relaxation over ~ 25 Å
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absorptionthe most intense transition is the vertical one
electronic excited state
S1
electronic ground state
S0
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because of the difference in equilibrium geometry between the ground state and excited state, the emission and absorption curves are displaced with respect to one another!
emission takes place from the lowest vibrational state of the electronic excited state
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absorption and emission in oligophenylene vinylenes
analysis of the vibronic progression using the displaced harmonic oscillator model
µtot (Si→ Sj; νm → νn) = µelect. (Si → Sj) * Fmn
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experimental absorption and emission spectra of oligophenylene vinylenes
77K in inert PMMA matrix
(Los Alamos)
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simulation of absorption
experiment(D.D.C. Bradley)theory
S1 relaxation energy decreases as chain grows
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simulation of emission
S1 relaxation energy:from ~ 0.27 eV in stilbene to ~ 0.15 eV in long chains
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h) the metal-on-polymer interface
evaporated metal atoms
ultra-thin polymer film (~ 50 Å)
in UHV (~ 10-10 – 10-11 Ton)
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Al on PPV
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principle of photoemission spectroscopy
W.R. Salaneck
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the aluminum / polyacetylene interface
diphenylpolyenes (DPn):
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analysis of the C(1s) shake-ups
“looking at π→π* transitions with XPS”
in DP7:separate contributions from:
the polyene chainthe phenyl rings
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Al /DP7 interface
the polyene electronic structure is strongly modifiedthe phenyl rings remain unaffected
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aluminum / polyene interface
Al-C covalent bond formationsp3-carbons; reduced conjugation
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sodium on diphenylpolyenes
DP1→7
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pristine DPx
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Na / DP7 interface
XPS C(1s)shake-ups
the shake-up due to the polyene part remains strong upon Na metallization in contrast to the Al case
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doping
the XPS core-level data indicate:* Na⊕* two sodiums per DPx
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sodium – doped DPx
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electronic-structure evolution due to chemistry at the interface
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low workfunction metal atoms on surfaces of conjugated polymers:
in context of polymer-based LED’s
Al: forms covalent bonds electrodeNa: acts as dopant Na+
Ca: acts as dopant for clean PPV Ca++
but as electrode material on oxidized PPV surfaces
there is always an interfacial region between the metal and the polymer
needs to be incorporated in the physics of these devices