1,721,063 research outputs found
Rationalizing the electronic properties of two classes of push–pull DSSC sensitizers based on Zn(II) di- or tetrarylporphyrinates substituted in meso or beta-pyrrolic positions: an electrochemical investigation
No full textPush–pull Zn(II)-porphyrinates have recently shown attracting performances as
light harvesting systems in dye-sensitized solar cells (DSSCs). To fully exploit their
intrinsically high efficiency it is important to finely tune their HOMO and LUMO levels,
which can be achieved by proper choice of the push and pull substituents. Of course
such target-oriented molecular design requires the availability of reliable relationships
between molecular structure and electronic properties; therefore we have carried out
a detailed electrochemical investigation, also supported by spectroscopy and
theoretical computations, on a wide, systematic range of Zn(II)-porphyrinates:
(a) a family of 5,15-meso substituted ones with phenylethynyl linkers, including a
first "benchmark" symmetric series carrying on the opposite terminals the same
substituent (N(CH3)2, OCH3, COOCH3, COOH, NO2); and a second push–pull one,
with the terminal positions carrying one donor and one acceptor group belonging to
the series above. Moreover, two suitably modified porphyrins allowed evaluation of
the effects of (i) the presence or absence of the phenyl group in the linker between
the porphyrin core and the acceptor group, and (ii) the effect of perfluorination on the
same phenyl group;
(b) a family of mono and, for the first time, disubstituted push-pull ZnIIporphyrinates
bearing a variety of ethynyl-phenyl moieties in β-pyrrolic position,
which were compared with their meso analogues, producing evidence that, although
the HOMO-LUMO energy gap of the meso substituted push-pull dyes is lower, the β
mono or disubstituted push-pull porphyrinic dyes show comparable or better
efficiencies when acting as sensitizers in DSSCs, possibly on account of a more
facile charge injection into TiO2.
A rationalization scheme is proposed concerning relationship between structure
and redox properties, affording inter alia interesting clues on the different localization
of the redox centres and the effective conjugation between the porphyrin core and
the side chains as a function of the molecular design.
References:
[1] P. R. Mussini, A. Orbelli Biroli, F. Tessore, M. Pizzotti, C. Biaggic, G. Di Carlo, M.
G. Lobello, F. De Angelis, Electrochimica Acta 85 (2012) 509– 523
[2] G. Di Carlo, A. Orbelli Biroli, M. Pizzotti, F. Tessore, V. Trifiletti, R. Ruffo, A.
Abbotto, A. Amat, F. De Angelis, P. R. Mussini, Chemistry-a European Journal, in
press (2013)
Stechiometria : dal testo di M. Freni e A. Sacco
No full textIl testo è stato completamente rinnovato e ampliato per renderlo più adatto alle esigenze di studio degli odierni corsi universitari. Gli Autori hanno cercato di apportare delle modifiche che, nel rispetto dello spirito del testo originario, consentissero di rinnovare parte dei capitoli, alleggerendo la trattazione di qualche argomento, ormai considerato “accessorio”. In ogni capitolo sono richiamate le conoscenze fondamentali e necessarie per affrontare la risoluzione dei problemi ed è stato aggiunto un capitolo sulle formule di Lewis che, nonostante sia una tematica non appartenente in senso stretto alla stechiometria “classica”, rappresenta comunque un bagaglio di conoscenza fondamentale per lo studente che voglia affacciarsi al mondo della chimica. Sono presenti un cospicuo numero di esercizi risolti e problemi con risoluzione e dei problemi di argomento biologico. Alla fine di ciascun capitolo, inoltre, sono stati inseriti dei problemi da risolvere per verificare l'apprendimento dei concetti chiave discussi. Il volume è completato da un capitolo di esercizi di ricapitolazione per fissare i concetti studiati in precedenza
Effect of the Coordination to the "Os3(CO)11" Cluster Core on the Quadratic Hyperpolarizability of trans-4-(4'-X-styryl)pyridines (X = NMe2, t-Bu, CF3) and trans,trans-4-(4'-NMe2-phenyl-1,3-butadienyl)pyridine
No full textCoordination to the “Os3(CO)11” cluster core of substituted styrylpyridines such as trans-4-(4’-NMe2-styryl)pyridine (L1), trans-4-(4’-t-Bu-styryl)pyridine (L2), trans-4-(4’-CF3-styryl)-pyridine (L3), or trans,trans-4-(4’-NMe2-phenyl-1,3-butadienyl)pyridine (L4) produces an enhancement of their quadratic hyperpolarizability, β EFISH, measured by the solution-phase dc electric-field-induced second harmonic (EFISH) generation method. This effect is due either
to a red-shift of the intraligand charge-transfer (ILCT) transition upon coordination (when the substituent in para position is a strong electron donor) or to a metal-to-ligand charge transfer (MLCT) transition (when the substituent is a strong electron acceptor). In the latter case the quadratic hyperpolarizability has a negative sign, due to the negative value of Δμeg. Therefore the “Os3(CO)11” cluster core displays an ambivalent acceptor or donor role. Some of the complexes investigated in this study show significant values (between 500x10-48 and 900x10-48 esu) of the product μβ0
Boosting the Oxide-based Chemoresistor Sensing Performances : the Role of Graphene Oxide and Porphyrins
No full textThe sensing of gas molecules is of fundamental importance for environmental monitoring, control of chemical processes, and so on [1]. Furthermore, recent success in non-invasive medical diagnostics, based on human’s breath analysis, is pushing forward the development of extremely sensitive gas sensors for ppb detection of specific analytes (e.g. acetone) [1,2]. In recent years, graphene-based gas sensors have attracted much attention and different structures have been developed showing high sensing performances [2]. However, they still suffer from several problems, which could be overcome by covering the graphene surface with metal oxides (MOS). Besides, thanks to the high chemical versatility, promising results could be also obtained by coupling porphyrin-based macrocycles to MOS nanoparticles. As such, boosted potentialities, especially in terms of tuned selectivity and low water interference, may be obtained. Therefore, the present work is aimed at evaluating and comparing the sensing performances at both mild temperatures (also exploiting the UV light) of SnO2 matrix coupled with two different porphyrins and graphene oxide (GO, in a SnO2/GO weight ratio of 32:1 [4]) materials towards the sensing of acetone molecules. Specifically, two zinc porphyrins have been adopted, namely zinc tetraphenylporphyrin (ZnTPP, inset of Fig. 1a) and a perfluorinated derivative of ZnTPP, possessing in β position a conjugated electron withdrawing linkers terminating in a cyanoacrylic group (ZnTPPF20-β-BDT-CN, namely ZnTPPF20, see inset of Fig. 1b). Figure 1 shows the sensing responses of the three hybrids obtained at 150 °C with and without the aim of UV irradiations. Notably, the sensor responses of ZnTPPF20 are about ten times more intense than those of ZnTPP@Sn and Sn32@GO, whose intensities are similar. The LOD is the same for all the samples, i.e. 600 ppb. By computing the response and recovery times, it can be stated that the former for the three hybrids is comparable, whereas the recovery time of SnO2–porphyrins are significantly longer. Switching the UV lamp on, the samples ability to sense acetone drastically changed. First, the LOD reached the 200 ppb for all the materials. Regarding the response intensities, ZnTPPF20 can guarantee the more intense sensor response, although all the composites showed similar values. As known by the numerous studies on dye sensitized solar cells, porphyrins can transfer photoelectrons towards the n-type MOS increasing the conductivity and decreasing the surface band bending [5]. The same mechanism can also be activated by an absorbed electron donor molecule. Under UV light, the highest occupied molecular orbital (HOMO) level of porphyrins is almost depleted of electrons and then their transfer from the absorbed molecule is expected to be more efficient
Photovoltaic energy prediction for new-generation cells with limited data: A transfer learning approach
No full textPhotovoltaic (PV) energy systems are receiving increasing attention, given their relative ease of installation, with 3rd generation technologies promising even simpler fabrication processes and less-intrusive installation possibilities. Therefore, methods for predicting the PV energy output are important to balance the production of other types of renewable sources and avoid wasting energy, with approaches based on machine learning models being especially studied in recent applications. In the case of new-generation cells, limited data is available to train such models, making the use of transfer learning a viable approach to increase prediction accuracy. However, no work in the literature has considered a transfer learning approach studying how much knowledge can be transferred between 2nd and 3rd generation PV technologies. In this paper, we propose the first approach in the literature based on machine learning and transfer learning for the PV energy prediction, in the case of new-generation PV technologies for which limited training data is available. We tested our method on data collected from several locations throughout the world, with results confirming the validity of the approach
ZnII-porphyrinates with a dithienylethylene moiety linked in β-pyrrolic position by different π bridges: a panchromatic-dye approach to PSSCs
No full textCoordination and organometallic compounds and inorganic-organic hybrid crystalline materials for second-order non-linear optics
No full textThis review concerns the main results obtained in the last few years by the research group at the Dept. di Chim. Inorg. Metallorg. e Anal. of the Univ. degli Studi di Milano, in the field of nonlinear optics. After a brief introduction on the basic concepts of nonlinear optics (NLO), the authors report the studies on the 2nd-order NLO properties of 1-dimensional (1D) and 2D coordination and organometallic compds. and hybrid inorg.-org. cryst. materials. The research allowed defining some general rules for the design of new appealing NLO compds. and to isolate and identify some new interesting photonic materials
The sulphonated nature of the ligand as origin of the "triflate effect" on the NLO properties of [ZnY2L2] (L = 4-trans-NC5H4(CHCH)C6H4NMe2) complexes
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