Conjugated phosphorescence

To create pure red phosphorescent emission, a systematic study of the ligand structure and the emission properties was carried out by Tsuboyama et al. (Scheme 3.85) [304], It was found that the red-shift of the phosphorescence is attributable to introduction of more conjugated ligands. 

A Kohler and J Wilson, Phosphorescence and spin-dependent exciton formation in conjugated polymers, Org. Electron., 4 179-189, 2003. 

M Sudhakar, PI Djurovich, TE Hogen-Esch, and ME Thompson, Phosphorescence quenching by conjugated polymers, J. Am. Chem. Soc., 125 7796-7797, 2003. 

YV Romanovskii, A Gerhard, B Schweitzer, U Scherf, RI Personov, and H Bassler, Phosphorescence of TT-conjugated oligomers and polymers, Phys. Rev. Lett., 84 1027-1030, 2000. 

D Hertel, S Setayesh, HG Nothofer, U Scherf, K Mullen, and H Bassler, Phosphorescence in conjugated poly(para-phenylene-derivatives), Adv. Mater., 13 65-70, 2001. 

Among the many excited singlet and triplet levels, 5i and Ti have distinct properties. They are in general the only levels from which luminescence is observed (Kasha rule) also most photochemical reactions occur from Sr or Ti. Here we discuss the characterization of the lowest triplet state by electronic spectroscopy. First we treat the theoretical background that allows the absorption spectra of conjugated systems to be described, and then we discuss the routes that lead to phosphorescence emission and Ti- - Sq absorption intensity. Details of the experimental methods used to determine triplet-triplet and singlet-triplet absorption spectra, as well as phosphorescence emission spectra are given in Chapters III, IV, and V. Representative examples are discussed. 

Ley and Schanze have also examined the luminescence properties of the polymers Pq, Pio> P25> and P50 in solution at 298 K, and in a 2-methyltetrahydro-furan solvent glass at 77 K. These spectroscopic studies reveal that fluorescence from the 71,71" exciton state is observed at Amax=443 nm, 2.80 eV in the polymers P0-P50 at 298 and 77 K, but the intensity and lifetime of the fluorescence is quenched as the mole fraction of Re in the polymers is increased. This indicates that the metal chromophore quenches the 71,71" state. The quenching is inefficient even when the mole fraction is large, suggesting that interchain diffusion of the 71,71" exciton is slow compared to its lifetime [70]. Phosphorescence from the 71,71" state of the conjugated polymer backbone is observed at > max=b43 nm, 1.93 eV in P10-P50 at 77 K, and emission at Amax=690 nm, 1.8 eV is assigned to the d7i(Re) 7i oiy MLCT transition. 

Hertel D, Setayesh S, Nothofer HG, Scherf U, Mullen K, Bassler H (2001) Phosphorescence in conjugated poly(para-phenylene)-derivatives. Adv Mater 13 65... 

Although the two compounds show similar photophysical behavior, the same is not true for their spectroscopic characteristics such as absorption, fluorescence, and phosphorescence maxima, where the bands in 43 are all red shifted relative to 44, suggesting less conjugation in the angular 44. In the case of 44, there is strong evidence for TTA in the singlet region. 

The optical and PL spectroscopies have been undertaken to understand the structure-property correlations of this important family of triplet-emitting polymers. The red shift in the absorption features upon coordination of the metal groups is consistent with there being an increase in conjugation length over the molecule through the metal center. The trade-olf relationship between the phosphorescence parameters (such as emission wavelength, quantum yield, rates of radiative and nonradiative decay) and the optical gap will be formulated. For systems with third-row transition metal chromophores in which the ISC efficiency is close to 100%,76-78 the phosphorescence radiative (kr)y, and nonradiative (/cm)p decay rates are related to the measured lifetime of triplet emission (tp) and the phosphorescence quantum yield ([Pg.300]

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