The intramolecular relaxation dynamics of semiflexible dendrimers in dilute solutions are theoretically investigated in the framework of optimized Rouse-Zimm formalism. Semiflexibility is implemented by modeling topological restrictions on the bond directions and orientations of the respective bond-vectors. Based on our recently developed approach for semiflexible dendrimers [A. Kumar and P. Biswas, Macromolecules 43, 7378 (2010)], the mechanical and dielectric relaxation moduli are studied as functions of local flexibility parameters and branching topology. It is rather interesting to observe that semiflexibility affects the local modes of G''(ω) and Δε''(ω), which have lower relaxation rate with increasing bond restrictions, while the collective modes with small relaxation rate remain almost constant. The relaxation dynamics of the flexible dendrimer is similar to that of the semiflexible dendrimer with unrestricted bond orientations (Φ = 0) and is flanked by the compressed (Φ = 30°) and expanded (Φ = 150°) conformations, respectively. The effect of semiflexibility is typically reflected in the intermediate frequency regime. The expanded conformations of semiflexible dendrimers display a power-law behavior in the intermediate frequency regime for both loss and storage modulus resembling fractal structures, while the compressed and unrestricted bond orientation conformations exhibit an approximately logarithmic dependence. The power-law exponent is found to be similar to the flexible dendrimers with excluded volume interactions. Thus, by tuning Φ, a spectrum of dynamic relaxation pattern is obtained spanning a broad range of conformations from a power-law fractal network to a non-fractal one. In certain limits, this highly generalized model captures the characteristics of flexible dendrimers and also resembles La Ferla's model semiflexible dendrimers. The influence of hydrodynamic interactions reduces the dynamical range and the width of the intermediate domain by decreasing the smaller relaxation rates and increasing the higher relaxation rates correspondingly.

The dilute solution dynamic properties of dendrimers are theoretically studied in the framework of an optimized Rouse−Zimm approach. Semiflexibility is implemented by modeling topological restrictions on the directions and orientations of the respective bond vectors. This accounts for the neglect of excluded volume interactions in the limit of short spacers. The transport properties, particularly, the behavior of intrinsic viscosity and translational diffusion coefficient are analyzed as functions of flexibility and dendrimer generational growth. The intrinsic viscosity reveals a characteristic maxima, as is experimentally observed in some cases. The value and position of the maxima varies with the topology of the molecule and is mainly dictated by the longest relaxation times. The diffusion coefficient shows a steady decrease for all topologically different conformations up to the fourth generation. The inclusion of hydrodynamic interactions accelerates the dynamics of all semiflexible dendrimer models by decreasing the respective range of intrinsic viscosity and diffusion coefficient values. The structural differences between the different conformations are manifest in the subsequent generations. These topologically dependent flexibility parameters provide suitable approximations to explore the intramolecular dynamics of real dendrimers.

We theoretically investigate the conformational properties of semiflexible dendrimers where the semiflexibility is implemented by topologically restricting the bond directions and orientations of the respective bond vectors. Molecular size (radius of gyration, R(g) and Wiener index, W), shape factor ρ, configurational free energy F, and the static structure factor, S(q) of semiflexible dendrimers are analyzed as a function of the bond orientation angle, φ. The size of the lower generation dendrimers decreases with increasing φ throughout the entire range of φ, φ ∈ (0, π). The higher generation dendrimers show a non-uniform behavior, for compressed conformations the size decreases with increasing φ, while for the expanded ones it increases with the increase in φ. A conformational transition occurs for the higher generation dendrimers from the limiting value of the hard sphere to an ideal chain with the change in φ. This conformational transition at φ = π∕2 is also reflected in the configurational free energy. The configurational free energy exhibits a discontinuous behavior with the variation of φ, and this discontinuity occurs at φ = π∕2. However, no such conformational transition is observed with the variation of the bond direction angle, θ, generation, G and functionality, f of the semiflexible dendrimers. The flexible dendrimer, i.e., at φ = π∕2 is flanked between the compressed and expanded conformations of the semiflexible dendrimers resembling a hard sphere. The Kratky plot of the structure factor of all conformations quantitatively match with the results obtained from experiments and simulations in the low q-region in respect to the position of the major Kratky peak. For higher wave numbers, the Kratky plots for all conformations of semiflexible dendrimers agree with earlier theoretical results of model dendrimers [R. La Ferla, J. Chem. Phys. 106, 688 (1997); F. Ganazzoli, R. La Ferla, and G. Raffaini, Macromolecules 34, 4222 (2001)] but are in sharp contrast to the experimental [S. Rathgeber et al., J. Chem. Phys. 117, 4047 (2002); S. Rathgeber, T. Pakula, and V. Urban, J. Chem. Phys. 121, 3840 (2004)] and simulated [M. L. Mansfield and L. I. Klushin, Macromolecules 26, 4262 (1993)] scattering curves for the higher generation dendrimers. All compressed conformations (0 < φ < π∕2) behave as compact hard spheres, while the expanded conformations (π∕2 < φ < π) are relatively more open, partially decongesting the steric crowding among the monomers with increasing φ.

A regioselective approach for the synthesis of pyrrolopyridinones and pyrroloazepinones is reported employing an Ugi reaction followed by a gold(I) or platinum(II) catalyzed intramolecular hydroarylation.