Restricted intramolecular rotation

Most of the molecules introduced in this chapter are hydrophobic. Even those molecules that have been functionalized to improve water-solubility (for example, CCVJ and CCVJ triethyleneglycol ester 43, Fig. 14) contain large hydrophobic structures. In aqueous solutions that contain proteins or other macromolecules with hydrophobic regions, molecular rotors are attracted to these pockets and bind to the proteins. Noncovalent attraction to hydrophobic pockets is associated with restricted intramolecular rotation and consequently increased quantum yield. In this respect, molecular rotors are superior protein probes, because they do not only indicate the presence of proteins (similar to antibody-conjugated fluorescent markers), but they also report a constricted environment and can therefore be used to probe protein structure and assembly. 

J. Chen, Z. Xie, J.W.Y. Chen, C.C.W. Law, and B.Z. Tang, Silole-containing polyacetylenes. Synthesis, thermal stability, light-emission, nanodimensional aggregation and restricted intramolecular rotation, Macromolecules, 36 1108-1117, 2003. 

Chen J, Law CCW, Lam JWY, Dong Y, Lo SMF, Williams ID, Zhu D, Tang BZ (2003) Synthesis, light emission, nanoaggregation, and restricted intramolecular rotation of 1,1-substituted 2,3,4,5-tetraphenylsiloles. Chem Mater 15 1535-1546... 

A static model does, however, not give a complete description of the molecule. It does not tell anything about the intramolecular movements, A more elaborate structure model has to be introduced in order to describe the more or less restricted intramolecular rotation that often takes place, or to describe the molecular vibrations. Force constants determining the intramolecular movements must also be considered as molecular structure parameters, along with the geometrical molecular structure parameters. So far no single... 

To separate die cooling effect from the glass effect, we choose dichlo-romethane (DCM), a liquid wifli much lower melting point, for the PL measurement. The PL intensity of die solution increases with a decrease in temperature in a nearly hnear fashion (Fig. 6B). This enhancement in emission must be due to the restricted intramolecular rotation caused by cooling-induced conformation freezing because the melting point of the solvent (-95°C) is lower than the lowest temperature we tested for this solution (-78°C). Similar to 3, polymers 2,4, and 7 also show much stronger emission when their solutions are cooled. 

Inclusion within the cavity results in restricted intramolecular rotational freedom in the guest. 

Eaton [62] reports a variety of effects of CD inclusion on the photophysical properties of a number of guests, including the effects of restricted intramolecular rotation, the inclusion of dimers, and the prevention of quenching by oxygen. 

Keywords Aggregation-induced enhanced emission (AIEE) Fluorescent organic nanoparticles Ion-association method Organic dye nanoparticles Reprecipitation method Restriction of intramolecular rotation Size-dependent optical properties... 

Organic dye nanoparticles of DHIA and DHBIA (the chemical structures are shown in Fig. 1) have been synthesized in THF/water mixed solvent by a reprecipitation method [32]. These dye molecules possess a 2-(2-hydroxyphenyl) benzothiazole (HBT) unit, which is known to be more stable as an enol imine form in the ground state and as a keto amine form in the excited state [32, 33] (Fig. 6). The nanoparticles exhibited the AIEE phenomenon mainly due to a restricted intramolecular motion, that is, impediment to free rotation of two end-substituted HBT units around single bonds. It is interesting to note that the... 

Most of the reported compounds which show this effect are organic molecules (179-184), where restriction of intramolecular rotation is generally accounted for being the main cause for AIE (175,185). The enhancement is therefore mostly related to the reduction of the nonradiative rate constant rising from the vibrational and rotational mode of the appended groups to the chromophores, which in the aggregates are strongly prevented. 

All of tl products l,3 triphenylbenzene, 1,3-diphenylpropane, 1,3,5-triphenylpen-tane, ethylbenzMie, methylben2 ne, and styrene are volatile products of thermal degradation of polystyrene This kind of intramolecular cyclization is not likely to be important in thermal degradation of poly(methyl methacrylate) and poly(a-methylstyrene), because the reactive site is linked to two bulky substituents which restrict the rotation of the terminal carbon atom containing the unpaired electron and thus prevent it from coming into proper orientation to attack the other carbon atoms in the chain. 

E (atact) = XiE (i) + XsE (s). The activation energy for the atactic samples was estimated to be 12.5 kcal/mol for MA and 7.5 kcal/mol for tBA, respectively. The values estimated from the assumption agree appreciably with experimental values. From the present work, it is concluded that the 3-relaxation of MA and tBA is attributed to the restricted internal rotation of the side chain, especially, to the rotation of Cj -C2 axis, and that the effective dip6le moment for the atactic samples can be estimated by means of the conformational analysis, thirdly that both and E depend principally on the intramolecular interaction between two nearest neighboring monomeric units. 

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