Photosensitivity of CuBiSe2 Thin Film Deposited by Vacuum Evaporation Technique

CuBiSe₂ (CBSe) thin film was prepared by vacuum evaporation. The deposited film was characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive X‐ray (EDX), UV–visible specroscopy, and I–V analysis. XRD analysis indicates the formation of cubic CBSe thin film, and the corresponding EDX spectrum confirms the stoichiometry composition of CBSe. In the AFM images, the majority of the particles are granular, and the surface roughness is 8.86 nm. The optical absorption coefficient is >10⁴ in the visible region and the bandgap energy is calculated to be 1.84 eV. The photosensitivity of the film is 181%.     

Long-lived higher excited state luminescence from new ruthenium(II)–allenylidene complexes

Resonance Raman spectra of heteroatom substituted ruthenium(II)-allenylidene complexes, obtained by irradiation into the second electronic absorption band, clearly prove the d(Ru)→π*(CCC) MLCT character of the corresponding electronic transition. The complexes are not significantly luminescent at room temperature, but in solvent glasses at 77 K, emission is observed. Only some of the complexes studied are luminescent upon irradiation into their lowest-energy absorption band. The striking finding of this study is that almost all complexes are luminescent on irradiation into their second absorption band. The emission was shown to originate from a higher lying ³MLCT state, which shows that internal conversion to the lowest excited state is very inefficient in these complexes.     

Simple and Dendritic Cyclam Derivatives. Photophysical Properties,Effect of Protonation and Zn2+ Coordination,Preliminary Screening as Inhibitors of Tumour Cell Growth

We have synthesized two novel dendrimers (BG1 and BG2) consisting of a 1,4,8,11-tetraazacyclotetradecane (cyclam, 1) core with appended four dimethoxybenzene and eight benzyl units (BG1) and twelve dimethoxybenzene and sixteen benzyl units (BG2). The absorption and luminescence spectra of these compounds and the changes taking place upon protonation and Zn²⁺ coordination of their cyclam core have been investigated in acetonitrile-dichloromethane 1:1 v/v solution. For comparison purposes, the absorption and luminescence spectra of 1,4,8,11-tetrabenzyl-cyclam (2), and dendrons BD1 and BD2, model compounds of the branches of BG1 and BG2 respectively, have also been studied. BD1, BD2, BG1, and BG2 exhibit the absorption and emission spectra of their 1,3-dimethoxybenzene unit, but in the two dendrimers the emission intensity is quenched by the cyclam amine groups and increases upon protonation and metal coordination. In order to test if these cyclam derivatives have an antitumour effect, we have studied their action on proliferation in the human neuroblastoma TS12 cell line. Screening experiments have shown that cell proliferation was (i) strongly reduced by the tetrabenzyl substituted cyclam 2, and (ii) unaffected by cyclam and the benzo dendrimers BG1 and BG2. Antitumour screening experiments have also been performed on the tetranaphthyl substituted cyclam 3 and the naphtho-dendrimer NG2, whose photophysical properties have been previously studied. Cell proliferation came out to be moderately reduced by 3, whereas dendrimer NG2 had no effect, similar to dendrimers BG1 and BG2.     

The emission of α,ω-diphenylpolyenes: A model involving several molecular structures

Available photophysical evidence for the emission of α,ω-diphenylpolyenes is shown to be consistent with a previously reported model [J. Catalán, J.L.G. de Paz, J. Chem. Phys. 124 (2006) 034306] involving two electronically excited molecular structures of 1B_u and C_s symmetry, respectively. The 1B_u structure is produced by direct light absorption from the all-trans form of the α,ω-diphenylpolyene in the ground state and its emission exhibits mirror symmetry with respect to the absorption of the compound. On the other hand, the C_s structure is generated from the 1B_u structure of the α,ω-diphenylpolyene by rotation about a C–C single bond in the polyene chain, its emission being red-shifted with respect to the previous one and exhibiting markedly decreased vibrational structure. At room temperature, both emissions give the excitation spectrum, which are ascribed to the first absorption band for the compound.     

Spectroscopy and photochemical reactivity of cyclooctadiene platinum complexes

The spectroscopic and photochemical properties of a series of 1,5-cyclooctadiene platinum complexes of the type [(COD)Pt(R)₂] (R=alkyl, alkynyl, or aryl) were examined. The observed photoreactivity is wavelength dependent and observed reaction rates correlate with the donor-strength of the R group. For strongly donating substituents like adamantylmethyl, benzyl or iso-propyl rates were increased by factors of about 100 for a given model reaction compared to the dimethyl derivative. The products were determined by NMR spectroscopy. Different reaction pathways were found depending on the substituents R. Theoretical calculations (DFT) on the electronic structure revealed the character of optical transitions and excited states.     

Pressure-Induced Free Exciton Emission in a Quasi-Zero-Dimensional Hybrid Lead Halide

Structural dimensionality and electronic dimensionality play a crucial role in determining the type of excitonic emission in hybrid metal halides (HMHs). It is important but challenging to achieve free exciton (FE) emission in zero-dimensional (0D) HMHs based on the control over the electronic dimensionality. In this work, a quasi-0D HMH (C₇H₁₅N₂Br)₂PbBr₄ with localized electronic dimensionality is prepared as a prototype model. With increasing pressure onto (C₇H₁₅N₂Br)₂PbBr₄, the broad and weak self-trapped exciton (STE) emission at ambient conditions is considerably enhanced before 3.6 GPa, which originates from more distorted [PbBr₄]²⁻ seesaw units upon compression. Notably, a narrow FE emission in (C₇H₁₅N₂Br)₂PbBr₄ appears at 3.6 GPa, and then this FE emission is gradually strengthened up to 8.4 GPa. High pressure structural characterizations reveal that anisotropic contraction of (C₇H₁₅N₂Br)₂PbBr₄ results in a noticeable reduction in the distance between adjacent [PbBr₄]²⁻ seesaw units, as well as an obvious enhancement of crystal stiffness. Consequently, the electronic connectivity in (C₇H₁₅N₂Br)₂PbBr₄ is sufficiently promoted above 3.6 GPa, which is also supported with theoretical calculations. The elevation of electronic connectivity and enhanced stiffness together lead to pressure-induced FE emission and subsequent emission enhancement in quasi-0D (C₇H₁₅N₂Br)₂PbBr₄.     

Synthesis, characterization and some properties of amide-linked porphyrin-ruthenium(II) tris(bipyridine) complexes

A new molecular dyad, comprised of a zinc-porphyrin and a ruthenium(II) tris(bipyridine) complex linked through an amide bond has been synthesized and characterized by ¹H, ¹³C NMR, UV-vis, mass-spectrometry and elemental analysis. The electrochemistry as well as the steady-state emission properties were investigated. The redox behavior of the dyad exhibits a favorable reversible characteristic. Substantial quenching of porphyrin emission was found when the Q band of 5 and 5-Zn was selectively photoexcited. This observation suggests a quenching mechanism with possible intramolecular electron transfer or energy transfer between the Ru(bpy)₃ moiety and the porphyrin free-base or Zn porphyrin moieties.     

Spectroscopy of Ru(II) polypyridyl complexes used as intercalators in DNA: Towards a theoretical study of the light switch effect

The absorption spectroscopy of [Ru(phen)₂dppz]²⁺ and [Ru(tap)₂dppz]²⁺ (phen = 1,10-phenanthroline, tap = 1,4,5,8-tetraazaphenanthrene; dppz = dipyridophenazine) complexes used as molecular light switches by intercalation in DNA has been analysed by means of Time-Dependent Density Functional Theory (TD-DFT). The electronic ground state structures have been optimized at the DFT (B3LYP) level of theory. The absorption spectra are characterized by a high density of excited states between 500 nm and 250 nm. The absorption spectroscopy of [Ru (phen)₂dppz]²⁺ in vacuum is characterized by metal-to-ligand-charge-transfer (MLCT) transitions corresponding to charge transfer from Ru(II) either to the phen ligands or to the dppz ligand with a strong MLCT () absorption at 411 nm. In contrast, the main feature of the lowest part of the vacuum theoretical spectrum of [Ru(tap)₂dppz]²⁺ between 522 nm and 400 nm is the presence of various excited states such as MLCT (), ligand-to-ligand-charge-transfer LLCT () or intra-ligand IL () states. When taking into account solvent corrections within the polarizable continuum model (PCM) approach (H₂O, CH₃CN) the absorption spectrum of [Ru(tap)₂dppz]²⁺ is dominated by a strong absorption at 388 nm (CH₃CN) or 390 nm (H₂O) assigned to a ¹IL () corresponding to a charge transfer from the outside end of the dppz ligand to the site of coordination to Ru(II). These differences in the absorption spectra of the two Ru(II) complexes have dramatic effects on the mechanism of deactivation of these molecules after irradiation at about 400 nm. In particular, the electronic deficiency at the outside end of the dppz ligand created by absorption to the ¹IL state will favour electron transfer from the guanine to the Ru(II) complex when it is intercalated in DNA.     

Photodegradation of poly(amidoamine) dendrimers peripherally modified with 1,8-naphthalimide units

This paper presents the photophysical and photochemical characteristics of four new poly(amidoamine) dendrimers of zero and second generation whose periphery has been modified with 1,8-naphthalimide units. Nitro- and allylamino groups have been used as substitutents at the C-4 position of the 1,8-naphthalimide fluorophores. The discussion is focused on the photodegradation of the dendrimers in N,N-dimethylformamide and dioxan solutions. Investigations have shown that the photodegradation of the dendrimers with 4-nitro substituted 1,8-naphthalimide proceed with yellow colour development in the solvent while no colour changes followed the same process in dendrimers with allylamino group substituent. The results also show that the photostability of the dendrimers depends on their generation.     

Subphthalocyanine fused dimers-C60 dyads: synthesis, characterization, and theoretical study

A donor-acceptor covalently linked dyad consisting of a subphthalocyanine fused dimer unit doubly-connected to a [60]fullerene has been prepared through double cycloaddition of the fused dimer, previously functionalized with aldehyde groups in the axial positions, to the fullerene (1,3-dipolar cycloaddition of azomethine ylides). The compound, isolated in several fractions, has been characterized and studied employing photophysical and electrochemical techniques. Molecular modeling of the distinct possible isomers was carried out using semiempirical methods.