Poly emission properties

S. Destri, M. Pasini, W. Porzio, G. Gigi, D. Pisignano, and C. Capolupo, Emission properties and solid-state aggregation in poly(fluorene-thiophene-5,5-dioxide) and in its model oligomer, Synth. Met., 138 289-293, 2003. 

Synthesis of several bridged macrocylic poly( -phenylene-vinylene)s 44 is also reported by Naso. The presence of such a ring structure improves the emission properties of the synthesized polymer more than that of non-bridged and branched polymer 45 (Equations (21) and (22)). 

Measuring the steady state optical absorption and emission properties of any luminescent polymer is the most basic but fundamental photophysical measurement we can make. Figure 1 depicts both the absorption and emission spectra for a series of polyfluorene oligomers and poly[9,9-di- -(2-ethylhexyljfluorene] (PF2/6), along with the fully rigid ladder type MeLPPP. 

BT5 and BT7. The redshift is 7 nm for BT3, 20 run for BT5 and 58 run for BT7. As in poly(3-hexylthiophene)s (P3HT), this shift is explained by a transition into an intramoleeularly higher ordered solid state strueture [4]. In aeeor-danee with this explanation the appearanee of a distinet vibronie structure is observed, especially for BT7 as also observed by other research group [29]. The PL emission maxima also show a bathochromic shift with increasing number of thiophene units. However, the PL spectra of BT5 and BT7 are very similar, due to essentially faster convergence of the emission properties. The solid state PL spectra reflect similar trends as described for the absorption properties. 

The emission properties of some carbazole double molecules [l,n-bis(JV-carbazoyl)alkanes] have been examined and one compound in particular, 1,3-bis-(N-carbazoyl)propane (1,3-BCP), was found to be a useful model for poly-(/V-vinylcarbazole). Measurements of the temperature dependence of monomer and excimer decay constants have provided useful kinetic and thermodynamic information on this system. The binding energy for the intramolecular excimer of 1,3-BCP was shown to be 2.76 kcal mol-1, a rather low value. Measurements on other carbazole double molecules showed that Hirayama s n = 3 rule is obeyed and that the preferred geometry of the intramolecular excimer is sandwichlike.161... 

The absorption and emission properties of bis[4-(dimethylamino)-phenyljsquaraine (3), bis[4-(dimethylamino)-2-hydrox5q)henyl]squaraine (21), bis(2,4,6-trihydroxyphenyl)squaraine (18), and an a2ulyl derivative of squaraine in poly(methyl methacrylate) and polystyrene have been reported [73]. The fluorescence lifetimes of new nanoseconds were observed for 3 and 21 in the polymer films, whereas for 18, the fluorescence lifetime was much shorter (10 ps). As discussed above, the neutral form of 18 is relatively nonfluorescent. A rapid excited state proton transfer tautomerization or deprotonation was proposed for the rapid deactivation of the excited state of 18. 

A methanol solution containing poly(3) exhibits abroad absorption band with A,max at 422 nm. In aqueous solution, the absorption maximum red-shifts to 432 nm and the absorption coefficient also decreases. The emission properties are greatly dependent upon the nature of the solvent. In a methanol solution, poly(3) exhibits a narrow emission band with A.max = 475 nm and a vibronic band at A,max = 502 nm. In aqueous solution, the emission band becomes broader and the fluorescence quantum yield (Ofi =0.016) is lower than that in methanol ( fi = 0.045). Interestingly, the emission maximum is at the same position as in methanol (475 nm) with a shoulder at 502 nm. Such behaviour is different from other PPE-based CPE, which exhibit large red-shifts of emission band in a poor solvent. The lack of a spectral shift for poly(3) is likely to be due to the fact that the aggregated state of the polymer has a much lower quantum yield, and therefore its contribution to the total emission spectrum is small. 

Fujita, Shinkai, and co-workers reported diacetylene-based gelators G3 containing four amide moieties [51]. By topochemical photodimerization of the diacetylene moieties, poly-diacetylenes were generated. Depending on the odd and even number of methylene moieties, the photoirradiated-gel showed red or blue colors. The photoelectric behavior like field emission properties of thin film made from these gels were also evaluated (Fig. 4.2). 

Poly(p-phenylenevinylene) (PPV) could be obtained in the form of nanotubes, nanorods and nanofilms by the chemical vapor deposition (CVD) polymerization of a,a -dichloro-/7-xylene followed by thermal dehydrochlorination. The polymerizations were conducted on the inner surface of or inside the nanopores of alumina or polycarbonate membrane filters or on the surface of silicon wafers. The PPVs thus obtained could be thermally converted to the corresponding carbonized tubes, rods, and films. We also could obtain nanopatterns and nanowells of PPV and carbon on silicon wafers by utilizing nanolithographed poly(methyl methacrylate) patterns. The PPV films obtained on the silicon wafers are semicrystalline and produce highly conducting (a 0.7 x 10 Scm ) graphitic films even when treated only at 850 C. Field-emission properties of some of the graphitic nanotubes are also described in this report. 

The polybenzofulvene derivatives bearing an ester group in position 2 of the indene moiety (e.g., poly-BFl, poly-BF3k) have been found to show intense emission bands around 440-460 nm (see Table 9 of Absorption and Emission Spectroscopy section), whereas the presence of snbstituents different from the COOR was found to decrease significantly the emission intensity (Fig. 54). This result complicated the study and the eventual exploitation of the emission properties of poly-BF3 derivatives... 

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