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Designing excited states: theory-guided access to efficient photosensitizers for photodynamic action.

Photodynamic therapy (PDT) is a treatment modality for certain malignant (skin, head and neck, gastrointestinal, gynecological cancers), premalignant (actinic keratosis), and nonmalignant (psoriasis) indications. Broader acceptance by the medical community and applicability is hampered, at least in part, by the less than optimal photophysical characteristics of the porphyrin derivatives. This situation sparked a worldwide search for novel sensitizers leading to new compounds, some holding more promise than others. The primary cytotoxic agent involved in the photodynamic action is singlet oxygen (Dg), the efficient generation of which is linked invariably to the intersystem crossing (ISC) efficiency of the excited sensitizer. Most organic dyes have low triplet quantum yields, and in many recent candidates for photodynamic sensitizers, heavy atoms are incorporated into the structure as a strategy to improve spin–orbit coupling leading to facilitated intersystem crossing. While this approach seems fail-safe, incorporation of heavy atoms such as bromine, iodine, selenium, and certain lanthanides very often leads to increased “dark toxicity”. Unlike traditional chemotherapy agents, in principle, photodynamic therapy sensitizers themselves can be nontoxic, either at cellular or organ levels, even at relatively high concentrations. We have been interested in trying to find alternative ways of achieving increased intersystem crossing without the use of heavy atoms to minimize dark toxicity, turning our attention to the excitedstate properties of the sensitizers. Designing efficient photoinduced O2 generators requires that any existing operative fluorescence cycle of the fluorophore, which is through the S0!S1!S0 states, has to be perturbed so as to minimize or shut down the S1!S0 deactivation, and switch to the triplet surface once S1 is accessed. A general design principle for a favorable S1!T1 transition from an electronic structure viewpoint would in principle require the structural and electronic compatibility of the S1 and T1 states to surpass that of the S1–S0 pair. Once multiple electronic states come into play, quantum mechanical calculations providing a detailed understanding of the electronic structure are extremely helpful. Multi-configurational self-consistent field (MCSCF) techniques are the stateof-the-art computational chemistry approaches, when near degeneracies and excited states are considered. These methods may not reach chemical accuracy ( 2–3 kcalmol ) for computing total energies, but they are crucial for a qualitatively correct description of the excited states and are capable of providing a conceptually complete picture of the photophysics taking place. Therefore, we mainly employed a popular variant of MCSCF techniques; the complete active space SCF (CASSCF) method in combination with relatively large basis sets and different active spaces. Details of CASSCF calculations are provided in the Supporting Information. Our calculations on the parent Bodipy (4,4-difluoro-4-bora-3a,4adiaza-s-indacene, Scheme 1) showed that natural orbital occupancies of the S1 state describe an open-shell singlet with essentially double (> 1.9) or zero (< 0.1) electrons for all orbitals except the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) that are singly occupied (see the Supporting Information, Figure S1). It is no surprise to observe a fluorophore with low triplet quantum yield to have an excited state that possesses only two orbitals with single occupancy. Hence, to achieve our goal of efficient switching to the triplet manifold, we have to access excited states that differ from the ones that arise from simple HOMO!LUMO transitions. Among multiply excited configurations, doubly substituted ones are particularly important in enhancing S1–T1 coupling as shown by the seminal work of Salem and Rowland and the following work by Michl. Thus, the substitutions should invoke a simultaneous two-electron excitation from the Scheme 1. Structure and numbering of the parent Bodipy compound. [*] Y. Cakmak, S. Kolemen, B. Kilic, Prof. Dr. E. U. Akkaya UNAM-Institute of Materials Science and Nanotechnology Bilkent University, Ankara, 06800 (Turkey) E-mail: eua@fen.bilkent.edu.tr

Solid-State Emissive BODIPY Dyes with Bulky Substituents As Spacers

Bright fluorescence of the BODIPY dyes, just like most other fluorophores, is quenched in the solid state due to reabsorption and self-quenching. However, introduction of bulky tert-butyl substituents on the meso-phenyl groups result in more spaced packing in the solid state, resulting in highly luminescent powders and films.

Bidirectional switching of near IR emitting boradiazaindacene fluorophores.

Two novel distyryl-boradiazaindacene dyes with dimethylaminostyryl and pyridylethenyl substituents display opposite spectral shifts on protonation with TFA in organic solvents. This bidirectional switching of the dyes can be shown to be directly related to ICT donor and acceptor characteristics of the substituents attached to the BODIPY core. The observed spectral response of these dyes could be very useful in the design of novel NIR fluorescent ratiometric probes for pH.

Synthesis and antidiabetic activity of morpholinothiazolyl-2,4-thiazolidindione derivatives

We report the synthesis and the in vitro insulin releasing and glucose uptake activity of the morpholino thiazolyl-2,4-thiazolidinediones (1-15). Compounds 5, 11–15 (at lower concentration; 0.001 mg/ml) were able to increase insulin release in the presence of 5.6 mmol/l glucose. The compounds, except derivative 3 show an increase of glucose uptake. Various compounds are interesting potential antidiabetic leads showing pancreatic and extrapancreatic effects.

Modeling the intermolecular interactions: molecular structure of N-3-hydroxyphenyl-4-methoxybenzamide.

The title compound, N-3-hydroxyphenyl-4-methoxybenzamide (3) was prepared by the acylation reaction of 3-aminophenol (1) and 4-metoxybenzoylchloride (2) in THF and characterized by ¹H NMR, ¹³C NMR and elemental analysis. Molecular structure of the crystal was determined by single crystal X-ray diffraction and DFT calculations. 3 crystallizes in monoclinic P2₁/c space group. The influence of intermolecular interactions (dimerization and crystal packing) on molecular geometry has been evaluated by calculations performed for three different models; monomer (3), dimer (4) and dimer with added unit cell contacts (5). Molecular structure of 3, 4 and 5 was optimized by applying B3LYP method with 6-31G+(d,p) basis set in gas phase and compared with X-ray crystallographic data including bond lengths, bond angles and selected dihedral angles. It has been concluded that although the crystal packing and dimerization have a minor effect on bond lengths and angles, however, these interactions are important for the dihedral angles and the rotational conformation of aromatic rings.

Spectroscopic, Magnetic and Crystal Structure Analysis of Diammine-bis(2,6-dibromo-4-chlorophenolato-O)copper(II)

The [Cu(C6H2Br2ClO)2(NH3)2] complex was synthesized and characterized by XRD, UV/vis, FTIR, DSC, elemental analysis and magnetic susceptibility measurements. The structural analysis of the title complex indicated that it is a monomeric centrosymmetric compound which crystallizes in the monoclinic system, P21/c, and has a trans-planar CuO2N2 coordination [Cu-O 1.940(5) and Cu-N 1.978(7) Å ]. In the coordination sphere of the Cu atom, there are long range interactions with Br2 and the centrosymetrically related Br2i (i: −x,−y,−z) atoms [Cu-Br2: 3.079(2) Å ], resulting in a tetragonally elongated octahedral structure for the CuO2N2Br2 coordination. The molecules form one-dimensional chains along the x-axis of the unit cell held together by intermolecular hydrogen bonds.