Intramolecular charge-transfer complexes

However, the cyclic voltammetry measurements showed two one-electron reduction waves very close to that observed for the parent TCNQ. This finding indicated that DBTCNQ behaves in solution as a simple 

Theoretical calculations carried out on the DBTCNQ molecule showed that the steric hindrance between the hydrogen phenyl ring and the olefinic hydrogen of the TCNQ moiety was responsible for the orthogonality found in the X-ray data [156]. Consequently, we carried out the synthesis of 7,7,8,8-tetracyano-2,5-bis(3-phe-nylpropyl)-p-quinodimethane (70) and N,A -dicyano- 

The X-ray structure [157] of the TCNQ derivative (70) showed a molecular geometry and packing arrangement similar to the former 2,5-dibenzyl-TCNQ (DBTCNQ) [154]. The central TCNQ ring is totally 

The cyclic voltammetry measurements of these compounds (70 and 71) indicate the presence of two one-electron reduction waves to the radical anion and dianion at reduction potential values similar to those of TCNQ and DCNQI, as shown in Table 1.12. The voltammograms did not show the presence of an oxidation wave corresponding to the radical cation, thus suggesting that these compounds also behave in 

---

Lukac S (1984) Thermally induced variations in polarity and microviscosity of phospholipid and surfactant vesicles monitored with a probe forming an intramolecular charge-transfer complex. J Am Chem Soc 106 4386 -392... 

Loutfy RO, Law KY (1980) Electrochemistry and spectroscopy of intramolecular charge-transfer complexes. p-N, N-dialkylaminobenzylidenemanononitriles. J Phys Chem 84 2803-2808... 

Fig. 20 Log EM for interaction of end-groups on polymer chains with average polymerisation degree 3c (i) pyridine-catalysed hydrolysis of the p-nitrophenyl ester group of [27] ( ) and [28] ( ) in aqueous solution (data from Sisido et at., 1976, 1978), (f i) intramolecular charge-transfer complexes of [29] in chloroform ( ) and in ethanol (O). (Data from Sisido et at., 1977 Takagi et at., 1977)...

Schiff bases with intramolecular charge transfer complexes such as 2,3-bis[(4-diethylamino-2-hydroxybenzylidene)amino]but-2-enedinitrile zinc (II) (BDPMB-Zn, 187) emit red fluorescence with fluorescent quantum yields up to 67%. OLEDs with a structure of ITO/TPD/ TPD BDPMB-Zn/Alq3 BDPMB-Zn/Alq3/Mg-Ag showed very bright saturated red emission with CIE (0.67, 0.32) with a luminance of 2260 cd/m2 at 20 V and a current efficiency of 0.46 cd/A (at 20 mA/cm2). In addition, the EL spectra do not change with the doping concentration in the range of 0.5—3% [229]. 

The desulphurization of disulphides by tervalent phosphorus compounds has been the subject of a review.70 The light-induced desulphurization of benzylic sulphides by phosphites has found further use in the synthesis of cyclophanes which exhibit the formation of intramolecular charge-transfer complexes, e.g. (61) and (62).71... 

It is possible to evaluate the strength of several acceptor parts (including some nitroaro-matic derivatives) in intramolecular charge transfer complexes in substrates such as 54 and 55 which also contain electron-donor fragments (X = PhNH—, PhO—, Ph—) from the oxidation potential of the complex and of the donor species161. 

Fox, Johnston, and co-workers (32) studied twisted-intramolecular-charge-transfer complexes in supercritical CHF3. Again, the charge-transfer process was governed by the proximity to the critical point. 

Kato et al. (1983) studied PVK containing three different intramolecular charge-transfer complexes, each containing a carbazole donor chromophore and a tricyanovinyl acceptor. The results were compared to PVK TNF and PVKiTCNE (telracyanoethylene) intermolecular complexes. Relative to the intermolecular complexes, intramolecular complexes show high primary quantum yields. The thermalization distances were about 22 A, less than 28 to 35 A for the intermolecular complexes. Differences in the structure of the intramolecular complexes caused slight differences in the primary quantum yield, but did not cause significant differences in the thermalization distance. 

However, on top of the inclusion phenomena, cyclophanes have more interesting properties to offer. In his first publication on cyclophanes, Cram [13] had already expressed his opinion about some peculiarities to be expected in cyclophanes, which he outlined as follows a) electronic interaction between aromatic rings placed face to face , b) the resulting influence on substitution reactions in the aromatic rings by transannular electronic effects, c) intramolecular charge transfer complexes and d) ring strain, steric strain and transannular strain. These effects have been studied on the parent compounds in detail [3]. 

Wagner and Liu have reported an interesting study of 1,4-biradicals formed by Norrish Type II processes. It is becoming evident that conformational equilibria in excited states can critically determine quantum yields for some Norrish Type II processes (Alexander and Uliana Lewis and co-workers). In some cases of this type, substituent effects have suggested that intramolecular charge-transfer complexation may be important (Kanaoka and Migita). 

For example, the excessive addition of sensitizer can result in crystallization of the sensitizer. Some sensitizers, even when present in low concentrations can result in over-sensitization of the composition, in that the photocurrent generated upon exposure will persist comparatively long after the illumination ceases. As an alternative to the sensitization by additives, intramolecular charge transfer complexes have been proposed, where the electron donor and electron acceptor functions are located along a common vinyl backbone. Examples are nitrated vinyl polymers of poly-(acenaphthylene), poly(9-vinylcarbazole) and poly(l-vinylnaphthalene), copolymers from 3,6-diphenyl-vinylcarbazoleand 3,6-dinitro-9-vinylcarb-azole. ° and copolymers from NVK and iV-vinylphthahntide. ... 

A. Inami and K. Morimoto. Electrophotographic materials comprising polymeric intramolecular charge transfer complexes. US Patent 3418 116, assigned to Matsushita Electric Ind Co Ltd, December 12,1968. 

Because of the possibility of forming inclusion compounds and intramolecular charge-transfer complexes, macrocyclic compounds furnished with an empty space of an appropriate size at the center of their molecules are of particular interest as artificial inclusion hosts. 

Y. Wang, K. Hang, N. A. Anderson, and T. Lian, 2003. Comparison of electron transfer dynamics in molecule-to-nanoparticle and intramolecular charge transfer complexes. J. Phys. Chem. B 107, 9434—9440. 

In the main chain of the polymer at the 3-position was linked into the side chain carbazole and thus it can produce charge through an induced intramolecular charge transfer complex in the visible region. The hole transport mechanism in macro-molecular structure of these materials was affected because of photoconductivity and hole hopping related between the molecular mobility of chromophore and the side chain carbazole units, and thus, the chemical anchorage to the polymer backbone generally depressed [58]. 

The UV/VIS absorption spectra of the polyurethane based on diphenyl-methane-4,4 -diisocyanate (4.77) is shown in Figure 4.11. Absorption peaks observed in the range 235-250 nm in aromatic urethane are due to (n, n ) transition of the intramolecular charge-transfer complex of the urethane, and broad absorption peaks in the 280-290 nm region are due to the n,n transition of the lowest excited state of the aromatic nucleus in the urethane group. 

The copolymers described above form intramolecular charge-transfer complexes which are deeply coloured and extend the spectral response of these materials into the visible and near infrared region [172]. Furthermore problems with the toxicity of acceptor molecules like TNF may be overcome by covalent fixation of acceptor groups to a polymer backbone. 

Similarly, intramolecular charge-transfer complexation was obtained by alternating copolymerization of tetracyanoquinodimethane (TCNQ) with ferrocene into one chain [91, 111]. Spectroscopic and electrochemical analyses of mixtures of the monomeric units showed clear intramolecular charge-transfer complexation. In a related study, poly(methylated ferrocenylsilanes) were shown to interact with tetracyanoethylene [262]. A similar concept is valid for viologen-based polymers [55]. 

Vinylidenecydopropanes as photoproducts have been generated in some cases. Chapman etal. have reported the formation of unsubstituted vinylidenecyclopropane by the photolysis of 2,6-diazocyclohex-anone in an argon matrix at 8 The photolysis proceeds via several intermediates such as diazoketene, cyclopropenone, and cyclopentyne. The photolysis of allenyl(vinyl)methane derivatives produced the vinylidenecyclopropane derivatives as main products via intramolecular charge transfer complexes. However, the photochemical behavior of these compounds has not been discussed. 

Coloured compounds are formed when phthalyl-tryptophan is incorporated into the same molecules as phenylalanine, the colour being ascribed to an intramolecular charge transfer complex. Optically active molecules have CD bands associated with the charge transfer bands. Using the area under the bands as a measure of complexing, association constants have been evaluated which agree with those obtained from absorption changes. 

---