Pyrazoline donors

This paper discusses the synthesis and physico-chemical consequences of binding low ionization 17-donors, such as TTF monocarboxylic acid (I) and l,3-di-(p-methoxyphenyl)-5-(p-hydroxyphenyl)-A2-pyrazoline (II) to a poly(vinylbenzylchloride) backbone. 

Hole transport in polymers occurs by charge transfer between adjacent donor functionalities. The functionalities can be associated with a dopant molecule, pendant groups of a polymer, or the polymer main chain. Most literature references are of doped polymers. The more common donor molecules include various arylalkane, arylamine, enamine, hydrazone, oxadiazole, oxazole, and pyrazoline derivatives. Commonly used polymers are polycarbonates, polyesters, and poly(styrene)s. Transport processes in these materials are unipolar. The mobilities are very low, strongly field and temperature dependent, as well as dependent on the dopant molecule, dopant concentration, and the polymer host This chapter reviews hole transport in polymers and doped polymers of potential relevance to xerography. The organization is by chemical classification. The discussion mainly includes molecularly doped, pendant, and... 

Hole mobilities of a series of pyrazoline, oxadiazole, and stilbene doped PC were described by Sugiuchi et al. (1991). The donor compounds were selected for differences in dipole moment and varied from 1.42 to 5.56 Debye. The results are shown in Fig. 96. The mobilities decrease with increasing dipole... 

Numerous unsuccessful attempts to synthesize cyclopropanethione have been reported. Thermal or photochemical generation of the C3H4S species from different sources always leads to allene episulfide. Some representative experiments include (a) in vacuo pyrolysis of the sodium salt of 2,2,4,4-tetramethylthietanone tosylhydrazone (4) into the stable tetramethylallene episulfide (S), (b) pyrolytic extrusion of nitrogen from perfluorinated thiadiazoline 6, (c) in vacuo pyrolysis of spiro compound 8 into methylenethiirane (3), (d) the flash vacuum pyrolysis-microwave spectroscopic approach applied to spiro compounds 9 and 10, (e) pyrolysis of anthracene adduct 11 and tosylhydrazide salt 12, (f) thermolytic nitrogen extrusion from pyrazoline-4-thione 13, thermolysis of tetramethylallene episulfide (5) or pyrazoline 13 in dig-lyme solution, and photolytic nitrogen extrusion from pyrazoline 13, ° (g) thionation of methylenecyclopropanone 15, and (h) reaction of donor-acceptor substituted allenes 18 with elemental sulfur. ... 

There continues to be an enormous amount of activity in the area of PET, much of it directed towards the development of systems capable of delivering artificial photosynthesis. Many of these systems involve porphyrin units as electron-donors and thus it is appropriate to consider them in this section of the review. A number of new fullerene-porphyrin dyads have been reported. A pyrazolinofullerene (155) has been constructed which facilitates efficient PET when strong donors such as iV,Ar-diethylaniline or ferrocene are linked to the pyrazoline ring. A photosynthetic multi-step ET model (156) based on a triad consisting of a meso,meso- inked porphyrin dimer connected to ferrocene and Ceo as electron-donor and electron-acceptor, respectively, has been synthesized and its ET dynamics (Scheme 38) have been investigated using time-resolved transient absorption spectroscopy and fluorescence lifetime measurements. ... 

Photophysical studies of various triaryl-2-pyrazolines in solution and in microcrystalline forms show that in solution triplet states are formed only by excitation transfer from a donor whilst by contrast they are formed directly in the microcrystalline... 

Using the 1,2-diazacyclopent-l-ene (pyrazoline) as a model of DBO allows the use of accurate yet computationally demanding (expensive) methods. In combination with experimental evidence, two mechanisms for quenching n,7T states were proposed (Sinicropi 2002 Sinicropi et al. 2000, 2001, 2002). DBO is efficiently quenched by hydrogen donors (for instance by solvents such as chloroform, methanol, and benzene) either via a concerted or a stepwise process. DBO luminescence can be quenched by electron donors (e.g., with triethylamine). 

Modified correlation diagram for the interaction of the n,7i -excited state of pyrazoline with an electron donor such as the trimethylamine reflecting the occurrence of an exciplexes and a conical Intersection along the reaction pathway (Redrawn with permission from ref. Sinicropi et al. 2000)... 

---