Andrea Previtali

H-Aggregates Granting Crystallization-Induced Emissive Behavior and Ultralong Phosphorescence from a Pure Organic Molecule

Solid-state luminescent materials with long lifetimes are the subject of ever-growing interest from both a scientific and a technological point of view. However, when dealing with organic compounds, the achievement of highly efficient materials is limited by aggregation-caused quenching (ACQ) phenomena on one side and by ultrafast deactivation of the excited states on the other. Here, we report on a simple organic molecule, namely, cyclic triimidazole (C9H6N6), 1, showing crystallization-induced emissive (CIE) behavior and, in particular, ultralong phosphorescence due to strong coupling in H-aggregated molecules. Our experimental data reveal that luminescence lifetimes up to 1 s, which are several orders of magnitude longer than those of conventional organic fluorophores, can be realized under ambient conditions, thus expanding the class of organic materials for phosphorescence applications.

Galois invariance, trace codes and subfield subcodes

Given a Galois extension we relate subfield subcodes with trace codes showing that a code is invariant under the Galois group if and only if its restriction coincides with the trace code.

Cyclic Triimidazole Derivatives: Intriguing Examples of Multiple Emissions and Ultralong Phosphorescence at Room Temperature

The performance of solid luminogens depends on both their inherent electronic properties and their packing status. Intermolecular interactions have been exploited to achieve persistent room-temperature phosphorescence (RTP) from organic molecules. However, the design of organic materials with bright RTP and the rationalization of the role of interchromophoric electronic coupling remain challenging tasks. Cyclic triimidazole has been shown to be a promising scaffold for such purposes owing to its crystallization-induced room-temperature ultralong phosphorescence (RTUP), which has been associated with H-aggregation. Herein, we report three triimidazole derivatives as significant examples of multifaceted emission. In particular, dual fluorescence, RTUP, and phosphorescence from the molecular and supramolecular units were observed. H-aggregation is responsible for the red RTUP, and Br substituents favor yellow molecular phosphorescence while halogen-bonded Br⋅⋅⋅Br tetrameric units are involved in the blue-green phosphorescence.

The Carter Subgroups of Some Classical Groups

It is shown that a Carter subgroup of a non-soluble unitary group can only be the normalizer of a Sylow 2-subgroup. This result, combined with previous results, implies that no finite simple group can be a minimal counterexample to the conjugacy conjecture of Carter subgroups in a finite group.

Maps behaving like exponentials and maximal unipotent subgroups of groups of Lie type

Let U be a maximal unipotent subgroup of a finite classical group in good characteristic. We prove the existence of a bijection between U and the associated Lie algebra preserving centralizers. As a consequence, we obtain information on the sizes of the conjugacy classes of U. Similar results are proved in the exceptional cases.

Irreducible constituents of monomial representations

We describe an algorithm for obtaining the central primitive idempotents of the algebra associated with a monomial representation. As a consequence, we obtain its irreducible constituents. This is implemented in Magma, using an algorithm based on Dixons modular approach. In the case of permutation representations, we get a simplified version of the algorithms of Michler and Weller.

Sets of transvections generating subgroups isomorphic to special linear groups

ABSTRACT The main result of this paper is a graph-theoretic necessary and sufficient condition, for a given set of transvections in SL(n, K) (n > 2 and K a finite field of characteristic not 2 or 3), to generate a group isomorphic to SL (m, L), for some m and some subfield L of K.

Another existence and uniqueness proof for the Higman-Sims simple group

In this article, we give a short proof for the existence and uniqueness of the Higman{Sims sporadic simple group HS by means of the flrst authors algorithm (17) and uniqueness criterion (18), respectively. We realize HS as a subgroup of GL22(11), and determine its automorphism group Aut(HS). We also give a presentation for Aut(HS) in terms of generators and relations. Furthermore, the character table of HS is determined and representatives of its conjugacy classes are given as short words in its generating matrices inside GL22(11).