Carbazole-trinitrofluorenone

Since semiconductor materials appear to be general candidates for third order effects, it is not surprising that photoconductive charge transfer complexes such as poly(vinyl carbazole)-trinitrofluorenone (PVK-TNF) would exhibit modest DFWM.(142) The observed nonlinearity at 602 nm, a wavelength absorbed by the CT complex, ranges from 0.2 - 2 x 10"11 esu, increasing as the molar fraction of TNF in the complex, PVK TNF, increased. Charge... 

Interest in the photoconductive properties of the carbazole nucleus has also prompted studies concerned with its incorporation into condensation polymers. Examples of polymers prepared include polyamides (34), polyesters (35) and polyurethanes (36) (80MI11105). Thorough studies on the CT interactions of these polymers with the monomeric acceptor 2,4,7-trinitrofluorenone have been done. In all cases, the formation constant for the CT complex was higher with polymers than for monomeric models. At least two polymer... 

The earliest all-organic photoconductive compositions consisted of poly-vinyl(carbazole) (PVK, 1) and 2,4,7-trinitrofluorenone (TNF, 2) [25], In spite of its historical importance, the PVK/TNF system is an unusual one, because it is one of the few photoconductors which acts simultaneously as a photogenerator of primary charges and the medium in which the charge transport is accomplished. It is much more usual to employ a separate charge generator and a distinct transport medium. 

Moreover, CT excitons are thought to be formed by intermolecular interaction in certain polymeric systems containing small molecules. A typical example is poly(N-vinyl carbazole) doped with trinitrofluorenone (TNF), a system which played a major role in early photoconductive studies on polymeric systems (see Chart 2.1). 

Chart 2.1 Chemical structures of po y N -vinyl carbazole) and trinitrofluorenone. 

Much work has been reported on the development of carbazole derivatives and also noncarbazole photoconductive polymers. An example of the latter group is poly(bis(2-naphthoxy)phosphazene), which is intrinsically an insulator with a very low photosensitivity toward both UV and visible radiation, but when doped with trinitrofluorenone in a 1 1 molar ratio, it is a strong photoconductor. 

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