Emission in solution

Since Forster s original work, a large number of aromatic compounds, including benzene, naphthalene, and anthracene, have been found to have concentration-dependent fluorescence spectra under some conditions. Most of these excimers are not as stable a.s the pyrene prototype, and require lower temperatures or higher concentrations to be observed.29 Some crystals also exhibit excimer emission. Crystalline pyrene, for example, has only a single structureless fluorescence band of the same energy as its excimer emission in solution.30... 

Leclerc and coworkers synthesized a 2,7-carbazolylenevinylene-thie-nylenevinylene copolymer 586 (04CM4619). Whereas this material showed red emission in solution (7.PL = 581 nm, Opl = 16%), it was not fluorescent in the solid state. 

Recent preparative studies of a series of mixed-ligand bpy and phen complexes of the formulation ds-[Re(CO)2(chelate)(diphos)]+ and cis-trans-[Re(bpy)(CO)2(PR3)2]+ (diphos is for example dppm or dppe) are emissive in solution with lifetimes in the range of 25 to 1147 ns and emission quantum... 

Table 1 Photophysical data for key representative platinum complexes that are emissive in solution at room temperature... 

Inspection of the data in Table II reveals a bathochromic shift of the of the triplet-triplet absorption with increasing solvent polarity, with a further bathochromic shift when the compound is adsorbed on microcrystalline cellulose. No phosphorescence emission in solution is seen from this compound at room temperature, indicating that the radiative lifetime of this triplet state is long. This is consistent with the lowest energy excited triplet state having predominantly (n, n ) character. The shape of the triplet-triplet absorption spectrum also suggests that this is the case(20). 

Nine years later, Leonhardt and Weller detected an excimer type emission in solutions containing perylene and dimethylaniline [80]. This first heteroexcimer has become the prototype of an ever expanding area of research. Perhaps the impact of these observations are best illustrated by the monograph dealing with the new phenomenom published only 12 years after the first report [81]. The significance of this research for the proper understanding of photo-induced electron transfer is born out by the first positive identification of a radical anion resulting from the irradiation of a donor-acceptor system in polar solvents (vide infra) [82]. 

Copolymers containing alternating l,4-bis(phenylethenyl)benzene, l,4-bis(phenylethenyl)-2,5-dimethoxybenzene or l,5-bis(phenylethenyl)naphthalene chromophores, and dibenzo-24-crown-8 spacers within the polymer backbone, best represented by 87, showed blue light emission in solution, and tunable photoluminescence and electroluminescence depending on the structure of the chromophore. Blends of these copolymers with a small amount of poly(ethylene oxide), and lithium salt as active layers, form efficient light-emitting electrochemical cells <2003JMC800>. 

When the bridge itself contains a potential electron donor or acceptor, the situation can be more complex. Thus, Tsujiya et al. [15] studied the intramolecular electronic interaction between anthracene (An) and dimethylaniline (DMA) in bridged systems, when the bridge contained an ethereal oxygen. In these systems it was found that the appearance of exciplex emission depended strongly on the relative position of the ethereal oxygen with respect to the anthracene part of the molecule. For l-An-0-(CH2)2 DMA, one conformer was found to exhibit no exciplex emission at all in the jet, whereas another showed both locally excited and exciplex emission. For l-An-CH2-0 CH2-DMA (and also for 9-An-CH2-0-CH2-DMA), no exciplex emission was found in the jet, although the same molecules show exciplex emission in solution It appears that the interaction between... 

To the best of our knowledge, there is only one paper by Mullen et al. [ 125] that presents the polymerization of the BIC unit. The semi-ladder polymer was synthesized by a nickel(0)-mediated Yamamoto-type polymerization using dichlorobisindenocarbazole or dibromobisindenocarbazole as precursors. The two polymers were synthesized in good yields (77 and 70%). They both show a strong blue emission in solution with a maximum centered at 445 nm. 

The protection against quenching offered by the CD cavity allowed, in some cases, the observation of phosphorescence emission in solution. Phosphorescence from 1-chloronaphthalene was observed in the presence of 10 M P-CD by steady-state excitation, while no signal could be detected in... 

In the solid state a bathochromic shift of the emission to 478 nm in 2a and to 507 in 2b occurs. The dramatic difference in luminescence must result from small changes in morphology, which enables the emission from excimers or other aggregates. Swager s pentypticene-containing PPEs (29, 30a) show almost invariant emission in solution and in the solid state (Table 11, entries 2—4). In 29 the emission (solution, 457 nm) is red-shifted by only 3 nm when fluores-... 

A series of homoleptic copper(i), silver(i), and gold(i) complexes of two bisphosphine ligands l,2-bis(diphenylphosphino)benzene, dppb bis[2-(diphenylphosphino)phenyl]ether, POP has been studied to demonstrate that these species are very low emissive in solution but highly luminescent in the solid state. In particular, the silver and copper complexes afford quite broad electroluminescence spectra with white light emission when used in the fabrication of light-emitting devices. ... 

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