Electronic structure and bonding of the 3d transition metal borides, MB, M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu through all electron ab initio calculations

The electronic structure and bonding of the ground and some low-lying states of all first row transition metal borides (MB), ScB, TiB, VB, CrB, MnB, FeB, CoB, NiB, and CuB have been studied by multireference configuration interaction (MRCI) methods employing a correlation consistent basis set of quintuple cardinality (5Z). It should be stressed that for all the above nine molecules, experimental results are essentially absent, whereas with the exception of ScB and CuB the remaining seven species are studied theoretically for the first time. We have constructed full potential energy curves at the MRCI/5Z level for a total of 27 low-lying states, subsequently used to extract binding energies, spectroscopic parameters, and bonding schemes. In addition, some 20 or more states for every MB species have been examined at the MRCI/4Z level of theory. The ground state symmetries and corresponding binding energies (in kcal/mol) are (5)Sigma(-)(ScB), 76; (6)Delta(TiB), 65; (7)Sigma(+)(VB), 55; (6)Sigma(+)(CrB), 31; (5)Pi(MnB), 20; (4)Sigma(-)(FeB), 54; (3)Delta(CoB), 66; (2)Sigma(+)(NiB), 79; and (1)Sigma(+)(CuB), 49. (c) 2008 American Institute of Physics

I. Structures and interaction energies of the van der Waals systems, C2H2-(H2O)x, x=1-4 and CHy-H2O, y=1,2 and II. Electronic structure of the carbides BC, BC-, HBC, AIC, AIC- and HAIC by ab initio calculations

The dissertation is divided in two parts. In the first one some very interesting and important van der Waals molecules are studied. The interaction of the acetylene molecule with water clusters (one up to four water molecules) is studied and 5, 6, 13 and 33 structures are calculated for the systems C2H2-H2O, C2H2(H2O)2, C2H2(H2O)3 and C2H2(H2O)4 respectively. Absolute energies, dissociation energies, fully optimized geometries and harmonic frequencies are given. The study of these clusters is important because acetylene is one of the few hydrocarbons that are soluble, even though slightly, in water. Through this study, the solubility of acetylene in water is explained. Moreover, the interaction of the methylidene CH and methylene CH2 with the water is investigated and all possible structures are calculated (7 and 10 structures respectively). Absolute energies, dissociation energies, geometries and harmonic frequencies are given. The study is important because CH is one of the most reactive radicals, whereas CH2 is the simplest carbene, is an important intermediate and forms an ylide with water. Last, both radicals play an important role in atmospheric chemistry. In the second part the diatomic molecules BC and AlC are studied by means of very accurate calculations. In total, 30 and 31 states are investigated respectively and the potential energy curves are plotted. Absolute energies, bond distances, dissociation energies, dipole moments, Mulliken charges and spectroscopic constants are calculated. In all states studied the bonding and the differences between the two molecules are commented on. Emphasis is given to the bonding of the ground state. For BC, the ground state is calculated systematically with a series of basis sets increasing size and different types. Furthermore, some states of the anions BC- and AlC- and the molecules HBC and HAlC, which are connected to the ground state of BC and AlC, are studied. Last, relativistic corrections were done for the ground state of both diatomics molecules.Η διατριβή χωρίζεται σε δύο μέρη. Στο πρώτο μέρος μελετώνται ορισμένα πολύ ενδιαφέροντα και σημαντικά μόρια van der Waals. Συγκεκριμένα μελετάται συστηματικά η αλληλεπίδραση του ακετυλενίου, C2H2 με συσσωματώματα (clusters) νερού Η2O (1 έως 4 μόρια) και υπολογίζονται 5, 6, 13 και 33 δομές για τα υπερμόρια C2H2-Η2O, C2H2(Η2O)2, C2H2(Η2O)3 και C2H2(Η2O)4 αντιστοίχως. Υπολογίστηκαν οι ολικές ενέργειες, οι πλήρως ελαχιστοποιημένες γεωμετρίες και οι αρμονικές συχνότητες. Η μελέτη του συστήματος είναι σημαντική διότι το ακετυλένιο είναι ένας από τους λίγους υδρογονάνθρακες οι οποίοι διαλύονται (έστω και ελάχιστα) στο νερό και μέσα από τη μελέτη αυτή ερμηνεύεται και δικαιολογείται η διαλυτοποίηση του. Μελετάται επίσης η αλληλεπίδραση του μεθυλιδενίου, CH και του μεθυλενίου, CH2 με το H2O, υπολογίζοντας όλες τις δυνατές δομές (7 και 10 δομές αντιστοίχως). Υπολογίστηκαν οι ολικές ενέργειες, οι πλήρως ελαχιστοποιημένες γεωμετρίες και οι αρμονικές συχνότητες. Η μελέτη των δύο συστημάτων είναι σημαντική διότι το CH είναι μία από τις πλέον δραστικές ρίζες, ενώ το CΗ2 είναι το απλούστερο καρβένιο, είναι σημαντικό ενδιάμεσο και σχηματίζει υλίδιο με το νερό. Τέλος, και οι δύο ρίζες παίζουν σημαντικό ρόλο στην ατμοσφαιρική χημεία. Στο δεύτερο μέρος μελετώνται με υπολογισμούς υψηλής ακριβείας τα διατομικά καρβίδια ΒC και AlC. Διερευνήθηκαν 30 και 31 καταστάσεις αντιστοίχως και κατασκευάστηκαν οι καμπύλες δυναμικής ενεργείας. Υπολογίστηκαν οι ολικές ενέργειες, τα μήκη δεσμού, οι ενέργειες δεσμού, τα φορτία κατά Mulliken, οι διπολικές ροπές και οι φασματοσκοπικές σταθερές. Σε όλες τις καταστάσεις ερευνήθηκε ο τρόπος σχηματισμού του δεσμού και σχολιάζονται οι διαφορές των δύο μορίων. Έμφαση δίνεται στο τρόπο σχηματισμού του δεσμού της θεμελιώδους καταστάσεως, θέμα το οποίο έχει απασχολήσει αρκετούς ερευνητές. Η θεμελιώδης κατάσταση του ΒC διερευνήθηκε συστηματικά με σειρά βασικών συνόλων αυξανομένου μεγέθους. Επίσης, υπολογίστηκαν ορισμένες καταστάσεις των ιόντων BC- και AlC- και των μορίων HBC και HΑlC οι οποίες συσχετίζονται με τις θεμελιώδεις καταστάσεις των ΒC και AlC. Τέλος, έγιναν σχετικιστικές διορθώσεις στις θεμελιώδεις καταστάσεις των ΒC και AlC

Physical Insights into Molecular Sensors, Molecular Logic Gates, and Photosensitizers in Photodynamic Therapy

In this article, the importance of charge/electron transfer in two rapidly growing areas of science is highlighted. In the field of molecular sensors, it plays a considerable role on the detection of molecular systems to serve as fluorescence sensors, switches, and molecular logic gates (MLG) replacing the semiconductor electronics, while in the field of photodynamic therapy, it acts competitive. On these scientific fields, a lot of research has been conducted in the last decades to find out potential candidates. In the field of fluorescent sensors, switches, and molecular logic gates, the fluorescent photo-induced electron transfer switching principle is responsible for the quenching of fluorescence. The manipulation of the quenching can lead to the design of an ideal candidate for complicated molecular logic operation. In the field of photodynamic therapy (PDT), the intersystem crossings occurring between excited singlet and triplet states are the key for an ideal photosensitizer (PS) candidate. The triplets must present relatively long lifetimes, and they must lie near or above the energy which is needed for the excitation of molecular oxygen. It this case, charge/electron phenomena can act competitive, and they are not desirable. However, there are a few complexes which are good PSs of singlet oxygen despite the charge transfer (CT) nature of their lowest excited state

Metallocene-Naphthalimide Derivatives: The Effect of Geometry, DFT Methodology, and Transition Metals on Absorption Spectra

In the present paper, the photophysical properties of metallocene-4-amino-1,8-naphthalimide-piperazine molecules (1-M2+), as well as their oxidized and protonated derivatives (1−M3+, 1-M2+-H+, and 1-M3+-H+), where M = Fe, Co, and Ni, were studied via DFT and TD-DFT, employing three functionals, i.e., PBE0, TPSSh, and wB97XD. The effect of the substitution of the transition metal M on their oxidation state, and/or the protonation of the molecules, was investigated. The present calculated systems have not been investigated before and, except for the data regarding their photophysical properties, the present study provides important information regarding the effect of geometry and of DFT methodology on absorption spectra. It was found that small differences in geometry, specifically in the geometry of N atoms, reflect significant differences in absorption spectra. The common differences in spectra due to the use of different functionals can be significantly increased when the functionals predict minima even with small geometry differences. For most of the calculated molecules, the main absorption peaks in visible and near-UV areas correspond mainly to charge transfer excitations. The Fe complexes present larger oxidation energies at 5.4 eV, whereas Co and Ni complexes have smaller ones, at about 3.5 eV. There are many intense UV absorption peaks with excitation energies similar to their oxidation energies, showing that the emission from these excited states can be antagonistic to their oxidation. Regarding the use of functionals, the inclusion of dispersion corrections does not affect the geometry, and consequently the absorption spectra, of the present calculated molecular systems. For certain applications, where there is a need for a redox molecular system including metallocene, the oxidation energies could be lowered significantly, to about 40%, with the replacement of the iron with cobalt or nickel. Finally, the present molecular system, using cobalt as the transition metal, has the potential to be used as a sensor