Excition delocalization

Emanuele E, Markovitsi D, Milli P, Zakrzewska K (2005) UV spectra and excitation delocalization in DNA influence of the spectral width. Chem Phys Chem 6 1387-1392... 

In addition, the excitation delocalization length of an aggregate could be estimated on the basis of the measurement of the aggregate radiative lifetime and its absorption spectrum half-width as described above [10, 11]. Such estimation, being interesting as itself, could also be regarded as the lower limit of physical dimension of the aggregate. 

Thus in the condensed phases the collision frequency, cage effect, primary excitation delocalization, and rapid excitation energy transfer will all tend to negate the chemical effects of excitation in saturated hydrocarbons. 

The following aspects will be addressed. (1) Conjugated polymers with benzene-derived repeat units (section II) typical examples are the already mentioned poly-/>phenylene (PPP) 6,43 polyphenylene-vinylenes (PPV) 9,43 and polyphenyleneethinylenes (PPE) 25.44 Some typical questions are obvious how do the aromatic or olefinic units interact via the formal single bonds and how far does an extra charge or an excitation delocalize over the chain. (2) Large... 

The photophysical properties of the self-assembled dimer [54]2 have been studied in detail with various spectroscopic and computational methods [53,54], In the lowest excited singlet (Si) state, the excitation delocalizes over the two macrocycles, and the non-radiative decay is enhanced by dimerization. By contrast, the exciton interaction is very weak in the lowest excited triplet (Ti) state. In the excited-state absorption spectrum recorded in 1-decane, two sharp bands at 658 and 694 nm are observed, which can be attributed to the Q bands of the Tx self-assembled phthalocyanine dimer. 

Migration clusters may be defined by intermediate-range interactions ( ). These give rise to intermediate-range bonds and clusters ("secondary clusters"). Excitation delocalization will usually happen within "primary clusters", defined by near neighbor interactions. 

The selection of systems reviewed clearly Illustrates the synthetic potential of bichromophoric molecules. It further emphasizes the role played by excitation delocalization and its impact on the choice of deactivation pathways available for the molecule. Systematic studies give an Insight into the dynamics of the linking chain, the importance of ground state interaction, and the role played by excited state complexes. 

A new area of energy-transfer research involves the use of strongly-coupled donor-acceptor moieties. Such systems are capable of displaying extremely fast excitation delocalization over several pigments. Similar studies have considered ultrafast energy relaxation in closely-coupled porphyrin dimers. 

Before we proceed to the case of crystals with two molecules per unit cell we should note that the so-called mean polarizability approximation which makes it possible to idealize the crystal as an array of molecules having mean polarizability given by eqn (5.35) is, actually, a very old approach. In former times (see, for instance, Section 6 of (15)), this approximation when applied to molecular systems with the van der Waals interaction was referred to as the additive refraction approximation . It should be stressed that, although eqn (5.38) provides just a very convenient extrapolation procedure, its accuracy increases with decreasing c so that the term linear in c in eqn (5.39) proves to be exact (but it does not take into account the effect of excitation delocalization discussed below). 

A) (excitation delocalized on the donor—acceptor complex, i.e., exciplex)... 

Fig. 13. Schematic model for electron injection of RuN3. Following MLCT excitation of the RuN3-sensitized Ti02 nanocrystalline film, electron injection occurs from both excited states of the dye, MLCT and MLCT, into the conduction band (CB) of the semiconductor. GS ground state of RuN3. Pathway A electron injection from the initially excited delocalized MLCT excited state. Pathway A2 ISC and localization in the MLCT excited state. Pathway B electron injection from the hot MLCT excited state of the attached bipyridine ligand (not observed in the present study). Pathway C internal vibrational relaxation in the MLCT excited state of the non-attached bipyridine ligand. Pathways D and E ILET between the bipyridine ligands and ensuing electron injection.

The bright states of the vertical excitation spectrum of 2-phenylfuran in gas phase are reported in Table 3. The full set of vertical transitions up to 7.4 eV is reported in Table SI of the Online Resource 1. The first two transitions are into a bright and a dark excimer states at 4.66 and 4.98 eV, respectively. The experimental band maximum in this region is at 4.55 eV in hexanes [16] and at 4.44 eV in methanol [45]. After a series of dark transitions into Rydberg states, a second band is characterized by a local nn excitation within the benzene ring (5.98 eV) and a nn excitation delocalized over the whole molecule. A very... 

---