150 research outputs found
Electrochemistry of cyclic triimidazoles and their halo derivatives: A casebook for multiple equivalent centers and electrocatalysis
A family of cyclic triazines, based on the triimidazo[1,2-a:1\u2032,2\u2032-c:1\u2033,2\u2033-e][1,3,5]triazine scaffold, has recently caught attention due to its variegated solid state photoluminescent properties (e.g., crystallization induced emission, fluomechanochromism, dual fluorescence, room temperature ultralong phosphorescence), tuned by proper functionalization of the cyclic core. From an electrochemical point of view, this family of heteroaromatic cyclic triazines is unexplored. A cyclic voltammetry study is here performed aiming to clarify structure/electroactivity relationship. The peculiar molecular structure of this class of molecules offers a multi-approach case study, spanning from multiple equivalent redox site interactions in small hoops (due to ideally C3h symmetry) to carbon-halogen bond reactivity in the presence of catalytic metal electrode surfaces (for \u2013Br and \u2013I derivatives). Results point to a poor heteroannular aromaticity along the rigid, planar cyclotrimer, with each equivalent redox site acting quite independently. An unusually higher electrocatalytic performance of gold with respect to silver electrode for the electrocleavage of carbon-halogen bonds (that decreases by increasing number of halo substituents) is tentatively explained in term of a specific interaction between gold and the nitrogen-rich planar cyclotrimer platform
Intrinsic and Extrinsic Heavy-Atom Effects on the Multifaceted Emissive Behavior of Cyclic Triimidazole
Considering that heavy halogen atoms can be used to tune the emissive properties of organic luminogens, the understanding of their role in photophysics is fundamental for materials engineering. Here, the extrinsic and intrinsic heavy-atom effects on the photophysics of organic crystals were separately evaluated by comparing cyclic triimidazole (TT) with its monoiodo derivative (TTI) and its co-crystal with diiodotetrafluorobenzene (TTCo). Crystals of TT showed room-temperature ultralong phosphorescence (RTUP) originated from H-aggregation. TTI and TTCo displayed two additional long-lived components, the origin of which is elucidated through single-crystal X-ray and DFT/TDDFT studies. The results highlight the different effects of the I atom on the three phosphorescent emissions. Intrinsic heavy-atom effects play a major role on molecular phosphorescence, which is displayed at room temperature only for TTI. The H-aggregate RTUP and the I c5 c5 c5N XB-induced (XB=halogen bond) phosphorescence on the other side depend only on packing features
Universality of 1/Q corrections to jet-shape observables rescued
We address the problem of potential non-universality of the leading 1/Q power
corrections to jet shapes emerging from the non-inclusive character of these
observables. We consider the thrust distribution as an example and analyse the
non-inclusive contributions which emerge at the two-loop level. Although
formally subleading in \as, they modify the existing na{\"\i}ve one-loop
result for the expected magnitude of the power term by a factor of order unity.
Such a promotion of a subleading correction into a numerical factor is natural
since the non-perturbative power terms are explicitly proportional to powers of
the QCD scale which can be fixed precisely only at the two-loop
level. The ``jet-shape scaling factor'' depends on the observable but remains
perturbatively calculable. Therefore it does not undermine the universal nature
of 1/Q power corrections, which remain expressible in terms of the universal
running coupling and universal soft-gluon emission.Comment: 21 pages, no figures, LaTeX. This revised version corrects a mistake
in the calculation of the two-loop correction factor. The conclusions remain
unchange
Centers of Mass and Rotational Kinematics for the Relativistic N-Body Problem in the Rest-Frame Instant Form
In the Wigner-covariant rest-frame instant form of dynamics it is possible to
develop a relativistic kinematics for the N-body problem. The Wigner
hyperplanes define the intrinsic rest frame and realize the separation of the
center-of-mass. Three notions of {\it external} relativistic center of mass can
be defined only in terms of the {\it external} Poincar\'e group realization.
Inside the Wigner hyperplane, an {\it internal} unfaithful realization of the
Poincar\'e group is defined. The three concepts of {\it internal} center of
mass weakly {\it coincide} and are eliminated by the rest-frame conditions. An
adapted canonical basis of relative variables is found. The invariant mass is
the Hamiltonian for the relative motions. In this framework we can introduce
the same {\it dynamical body frames}, {\it orientation-shape} variables, {\it
spin frame} and {\it canonical spin bases} for the rotational kinematics
developed for the non-relativistic N-body problem.Comment: 78 pages, revtex fil
Tuning the Linear and Nonlinear Optical Properties of Pyrene-Pyridine Chromophores by Protonation and Complexation to d10 Metal Centers †
The linear and second-order nonlinear optical (NLO) properties of two pyrene-pyridine chromophores, namely, 4-(pyren-1-yl)pyridine (L1) and 4-(2-(pyren-1-yl)ethyl)pyridine (L2), were investigated and modulated by performing protonation/deprotonation cycles or by complexation to d10 metal centers such as Zn(II) and Cu(I) to form the monomeric [Zn(CH3CO2)2(L1)2] complex and the [CuI(L2)]n coordination polymer, respectively. The structures of L1, L2, [Zn(CH3CO2)2(L1)2] and [CuI(L2)]n were determined by means of single-crystal X-ray diffraction studies. The NLO response, measured by the electric-field-induced second harmonic generation (EFISH) technique, was positive for both chromophores and showed an inversion of the sign after exposure to HCl vapors. This process was completely reversible and the original values were restored by simple exposure to NH3 vapors. Coordination of L1 to Zn(II) also resulted in a negative NLO response, although smaller in magnitude compared to the protonated form, due to the weak Lewis acidity of the \u201cZn(CH3CO2)2\u201d fragment. The results were also interpreted on the basis of DFT/TDDFT calculation
Unravelling the intricated photophysical behavior of 3-(pyridin-2-yl)triimidazotriazine AIE and RTP polymorphs
The development of purely organic materials showing multicolor fluorescent and phosphorescent behaviour represents a
formidable challenge in view of practical applications. Herein the rich photophyisical behaviour of 3-(pyridin-2-
yl)triimidazotriazine (TT-Py) organic molecule, comprising excitation-dependent fluorescence and phosphorescence under ambient conditions in both blended film and crystalline phase, is investigated by means of steady state, time resolved and ultrafast spectroscopies and interpreted on the basis of X-ray diffraction studies and DFT/TDDFT calculations. In particular, by proper excitation wavelength, dual fluorescence and dual phosphorescence of molecular origin can be observed together with low energy phosphorescences resulting from aggregate species. It is demonstrated that the multiple emission property is originated by the copresence, in the investigated system, of an extended polycyclic nitrogen-rich moiety (TT), strongly rigidified by p-p stacking interactions and short C\u2013H...N hydrogen bonds, and a fragment (Py) featuring partial conformational freedom
Solid State Room Temperature Dual Phosphorescence from 3-(2-Fluoropyridin-4-yl)triimidazo[1,2-a:1′,2′-c:1″,2″-e][1,3,5]triazine
Organic roomtemperature persistent luminescence is a fascinating but still largely unexplored
phenomenon. Cyclic-triimidazole and its halogenated (Br, I) derivatives have recently revealed as
intriguing phosphors characterized by multifaceted emissive behavior including room temperature
ultralong phosphorescence (RTUP) associatedwith the presence ofH-aggregates in their crystal structure.
Here, we move towards a multicomponent system by incorporating a fluoropyridinic fragment on the
cyclic-triimidazole scaffold. Such chromophore enhances the molecular properties resulting in a high
photoluminescence quantum yield (PL QY) in solution but preserves the solid-state RTUP. By means of
X-ray diffraction (XRD) analysis, theoretical calculations, steady-state and time-resolved spectroscopy
on solutions, polymethylmethacrylate (PMMA) blends and crystals, the nature of the different radiative
deactivation channels of the compound has been disclosed. In particular, the molecular fluorescence
and phosphorescence, this latter observed in frozen solution and in PMMA blends, are associated
to deactivation from S1 and T1 respectively, while the low energy RTUP, observed only for crystals,
is interpreted as originated from H aggregates
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