Excitation delocalised

The excitation delocalises over the aromatic rings conjugated with the CO2, producing the neutral form of coelenteramide in the excited state (2H ). 

Resonance states in the excited state carotenoid allowing delocalisation and stabilisation of the excited state. 

The mechanism of control with multipulse excitation is likely due to dynamics of the carotenoid donor. The presumably incoherent EET process [1] would not support the observed dependence on the carrier phase via the parameter c. Furthermore, the control effect does not suffer from annihilation at higher excitation intensities [2], as would be characteristic for the delocalised excitons in the B850 ring [1], However, it is well known that femtosecond pulses populate higher ground state vibrational levels by impulsive Raman scattering (IRS) [4], and that the periodic phase modulation (Eq. 1) makes IRS selective for specific vibrations... 

Excitation of the polymer creates one electron and a hole on the chain. This effect is particularly important when the electron-hole interactions are strong. Coulomb attraction keeps them together and we consider the two opposite charges as a bound electron-hole pair. An exciton (Fig. 1.11) is named according to its delocalisation. If it is localised, it is called a Frenkel exciton and, if it is delocalised, i.e., it extends over many molecular units, it is a Mott-Wannier type of exciton. ... 

One idea was that conduction should be looked for in materials based on organic unsaturated molecules, where electrons and holes are more easily excited into delocalised states. Little proposed that, in these materials, carriers created by such excitonic excitations could couple into electrons and holes plasmons, as later indeed observed in classical semiconductors under light, and thus produce a conductive state hopefully a superconductor state could develop under the same electron-electron interactions, leading possibly to high T<. s. The search for such excitonic conduction had been initiated shortly before as a porposal by W. Kohn for normal covalent semiconductors it had been carried out notably by D. Jerome, when he came to Orsay after on year s stay with Kohn in La Jolla various mineral semiconductors were studied, with small gaps and often low dimensionally. 

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