Stability of dibromo-dipyrromethene complexes coordinated with B, Zn, and Cd in solutions of various acidities

The spectral luminescent properties of dipyrromethenates halogenated with bromine on both ends of the long axis and coordinated using boron fluoride, zinc, or cadmium in neutral ethanol and acidified with hydrochloric acid solutions were studied. The constants of the acid–base equilibrium of the complexes in the proton-donor solvents in the ground and excited states was determined. The mechanisms of complex protonation were discussed, depending on the structure of the compounds. The electronic structures of the neutral and protonated compounds were modeled and analyzed based on the quantum-chemical method. The structures and spectral-luminescence properties were calculated using the SMD model of ethanol solvent using the TD-DFT theory with the B3LYP functional and the composite def2-SVP/def2-TZVP/def2-TZVPP_ECP basis sets, depending on the atomic number of the elements

Structure and formation of luminescent centers in light-up Ag cluster-based DNA probes

Fluorescent beacons based on silver (Ag) clusters for DNA/RNA detection represent a new type of turn-on probe that fluoresces upon hybridization to target nucleobase sequences. Physical–chemical mechanisms of their fluorescence activation still remain poorly understood. We studied in detail the fluorescence activation of dark Ag clusters induced by interactions of Ag–DNA complexes with different DNA sequences. In all cases, the final result depends neither on the location of the precursors (dark clusters) nor on their spectral properties. The reaction of fluorescence activation is a process similar to the growth of fluorescent silver clusters on dsDNA matrices. In both cases, reactants are dark clusters and two adjacent DNA strands. The latter form a double-stranded template for cluster nucleation. We found the optimized structure of a green fluorescent Ag4+2 cluster assembled on a C3/C3 DNA dimer in two different ssDNA pairs using QM modeling. The calculated absorption spectra match nicely the experimental ones, which proves the optimized structures. We conclude that apparent fluorescence activation in the studied systems results from reassembling Ag clusters on the new dsDNA template formed upon hybridization with the target. The suggested mechanism of “fluorescence activation” offers a way to design new light-up DNA probes. Two DNA strands making up the dsDNA template providing a high yield of bright Ag clusters can be used as the halves with the “stick” tails hybridizing with the base sequence of the target DNA. In this way, we have designed a light-up Ag cluster probe for β-actin mRNA

Luminescence Solvato- and Vapochromism of Alkynyl-Phosphine Copper Clusters

The reaction of [Cu(NCMe)4][PF6] with aromatic acetylenes HC2R and triphosphine 1,1,1-tris(diphenylphosphino)methane in the presence of NEt3 results in the formation of hexanuclear Cu(I) clusters with the general formula [Cu6(C2R)4{(PPh2)3CH}2][PF6]2 (R = 4-X-C6H4 (1-5) and C5H4N (6); X = NMe2 (1), OMe (2), H (3), Ph (4), CF3 (5)). The structural motif of the complexes studied consists of a Cu6 metal core supported by two phosphine ligands and stabilized by σ- and π-coordination of the alkynyl fragments (together with coordination of pyridine nitrogen atoms in cluster 6). The solid state structures of complexes 2-6 were determined by single crystal XRD analysis. The structures of the complexes in solution were elucidated by (1)H, (31)P, (1)H-(1)H COSY NMR spectroscopy, and ESI mass spectrometry. Clusters 1-6 exhibit moderately strong phosphorescence in the solid state with quantum yields up to 17%. Complexes 1-5 were found to form solvates (acetone, acetonitrile) in the solid state. The coordination of loosely bound solvent molecules strongly affects emission characteristics and leads to solvato- and vapochromic behavior of the clusters. Thus, solvent-free and acetonitrile solvated forms of 3 demonstrate contrasting emission in orange (615 nm) and blue (475 nm) regions, respectively. The computational studies show that alkynyl-centered IL transitions mixed with those of MLCT between the Cu6 metal core and the ligand environment play a dominant role in the formation of excited states and can be considerably modulated by weakly coordinating solvent molecules leading to luminescence vapochromism.This research has been supported by St. Petersburg State University Research Grant 0.37.169.2014, and Russian Foundation for Basic Research Grants 13-03-00970, 14-03-32077, and 13-03-12411. Academy of Finland (Grant 268993/2013, I.O.K), University of Eastern Finland (strategic funding—Russian–Finnish collaborative project), is also gratefully acknowledged. The work was carried out using equipment of the Analytical Center of Nano- and Biotechnologies of SPbSPU with financial support of the Ministry of Education and Science of Russian Federation; Centers for Magnetic Resonance, X-ray Diffraction Studies, Chemical Analysis and Materials Research, Optical and Laser Materials Research; and Computer Center of St. Petersburg State University

Statistical Method to Describe Molecular Spectra

The method to reproduce optical spectra by statistical treatment of quantum-mechanical calculations of energy states and photophysical properties in molecular conformers obtained during molecular-dynamical simulation was developed. Polycyclic organic molecules in solvents under thermo-dynamical conditions were considered. This technique was employed to build the first absorption band of estradiol, benzene, and anthracene. Increasing of the spectral intensity in benzene under temperature growth was demonstrated for the lowest excited state. Anthracene emission spectrum was built as well.Предложен метод для воспроизведения оптических спектров статистической обработкой квантово-механических расчетов энергетических состояний и фотофизических свойств в молекулярных конформерах, полученных в течение молекулярно-динамической симуляции. Обсуждены некоторые полициклические органические молекулы в растворах при различных термодинамических состояниях. Данный метод был применен для построения первых полос поглощения эстрадиола, бензола и антрацена. Продемонстрировано увеличение спектральной интенсивности бензола с ростом температуры для низшего возбужденного состояния. Также построен спектр излучения антрацена

The Influence of Thermodynamical Conditions on the Photophysical Properties of Cyanoantracene

Semi-empirical Quantum-Chemical calculations of the photophysical molecular properties of cyanoanthracene and surrounding argon cell under different thermodynamical conditions were performed using the MD DL_POLY code. Photophysical scheme of the lowest energy levels and transition probabilities was plotted for the individual molecule. Vibrational profiles of the long-wave absorption electronic band and the first excited Frank-Condon singlet state with fluorescent live-times of the oscillating molecule were obtained. Based on the theoretical results, experimental spectroscopic data have been interpreted.Проведены полуэмпирические квантово-химические расчеты фотофизических свойств цианоантрацена в ячейки с аргоновым растворителем при различных термодинамических условиях. Использован MD DL_POLY пакет. Построена фотофизическая схема низших уровней с вероятностями переходов для изолированной молекулы. Получены колебательные профили длинноволновой электронной полосы поглощения и первого возбужденного Франк-Кондоновского синглетного состояния с учетом флуоресцентного времени жизни для осциллирующей молекулы. Дана интерпретация экспериментальных спектроскопических данных