Showing papers by "Edamana Prasad published in 2011"
TL;DR: The design, synthesis, and the photophysical properties of a Low Molecular Weight Gel based on AB(3) and AB(2) type poly(aryl ether) dendrons with an anthracene chromophore attached through an acylhydrazone linkage are described.
162 citations
TL;DR: It is shown that pyrene-modified PAMAM dendrimers can be effectively utilized to generate wavelength-tunable emitting systems displaying bluish green, greenish yellow, and orange-red colors at room temperatures, and that general and specific solvent effects play a crucial role in the positive solvatochromism exhibited by the system.
Abstract: Significant aggregation is observed in pyrene-modified zero- and first-generation polyamidoamine (PAMAM) dendrimers above their critical aggregation concentration (CAC, >10(-6) M). The pyrene units are attached to the dendrimer skeleton through imine bonds, which play a pivotal role in enhancing the aggregation propensity of the PAMAM dendrimers. Scanning electron microscopy studies suggest that pyrene-modified PAMAM dendrimers aggregate into doughnut-shaped assemblies. As a result of aggregation, the pyrene chromophores are pre-arranged in a face-to-face geometry in the ground state, and readily generate pyrene "static excimer" on photoexcitation. The static pyrene excimer emits with an unprecedented quantum yield of 0.62 ± 0.01 in dichloromethane, and also exhibits remarkable positive solvatochromism from 498 to 638 nm, which leads to the highest bathochromic shift for pyrene excimer emission in solution reported so far. Lippert-Mataga analysis of the system suggests that general and specific solvent effects play a crucial role in the positive solvatochromism exhibited by the system. Luminescence quenching studies on both monomer and aggregate systems were carried out in the presence of various metal ions, and the results imply that pyrene-modified PAMAM dendrimer can be utilized for selective detection of Hg ions in the presence of a wide variety of transition, alkali, and alkaline earth metal ions. This report presents the first dendrimer-based chromophoric system exhibiting positive solvatochromism over a range of 140 nm, and shows that pyrene-modified PAMAM dendrimers can be effectively utilized to generate wavelength-tunable emitting systems displaying bluish green, greenish yellow, and orange-red colors at room temperatures.
46 citations
TL;DR: In this paper, the authors reported the synthesis, gelation and photophysical properties of luminescent AB3 type poly(aryl ether) dendron derivatives in the absence of conventional multi-interactive gelation motifs.
Abstract: We report the synthesis, gelation and photophysical properties of luminescent AB3 type poly(aryl ether) dendron derivatives in the absence of conventional multi-interactive gelation motifs. The gelation process is controlled through employing partial polar solvent milieu, which significantly enhances the propensity of π–π interaction between the aryl units present in the system. The self-assembly leads to unprecedented gelation through entrapping solvent molecules in the fibrillar arrangement of poly(aryl ether) units. The strategy was further utilized to prepare an excimer based photoluminescent gel through incorporating anthracene units in the dendrons. The close proximity between the anthracene units in the gel renders the formation of anthracene excimers at room temperature, resulting in the emission of bright green light from the gel, upon UV excitation. The study suggests that the size and packing of the self-assembled fibre can be controlled by the generation and functional groups present in the dendron. Furthermore, the strategy envisages an easy approach to generate fluorescent Low Molecular-mass Organic Gelator (LMOG) through incorporating poly cyclic aromatic hydrocarbon units to the poly(aryl ether) dendrons, since the self-assembly is largely guided by π–π interactions.
27 citations
TL;DR: In this paper, the ground state aggregation of PAMAMAM dendrimers with naphthalene units leads to significant ground-state aggregation in the system above the critical aggregation concentrations (CAC).
Abstract: Peripheral functionalization of PAMAM dendrimers with naphthalene units leads to significant ground state aggregation in the system above the critical aggregation concentrations (CAC). Upon photo-excitation of the ground state aggregates, static type excimer formation of naphthalene moiety is observed. Significant red-shifted emission from naphthalene excimers is achieved through generating the static type excimers in polar solvents such as methanol and acetonitrile-water mixtures. Control experiments suggest that the presence of dendritic scaffold in the system play a pivotal role in generating intense static excimer emission in naphthalene modified PAMAM dendrimers, in solution phase at room temperature.
11 citations