Volume 3, Issue 1

The interfacial structure made from the thermally deposited 5 – 7 nm thick layers of hexadecafluoro copper phthalocyanine (F 16 -CuPc) and of the unsubstituted copper phthalocyanine (CuPc) was subjected to the studies. The surface work function and the density of the unoccupied electron states (DOUS) located 5- 20 eV above the Fermi level (EF) were investigated during the CuPc/F 16 -CuPc interface formation using the very low energy electron diffraction (VLEED) method and the total current spectroscopy (TCS) measurement scheme. The DOUS peak structure of the organic films studied obtained from the TCS results showed a good correspondence to the main π* and σ* DOUS bands obtained from the density functional theory (DFT) calculations. The interfacial barrier was characterized by the negative charge transfer from the CuPc overlayer to the F 16 -CuPc underlayer occurred within the 5 nm thick interfacial region in the CuPc overlayer which was accompanied by the decrease of the surface work function from 4.9±0.1 eV to 4.3±0.1 eV. The stabilization of the π* DOUS bands, as well as restructuring of the low lying σ* bands was observed in the in the case of the fluorinated film (F 16 - CuPc) compared to the case of the unsubstituted CuPc film.

The review presents the state-of-the-art analysis of investigations in the field of a new line of research of photochromism – nanophotochromism. The design, properties, and possible applications of photochromic nanoparticles prepared by different methods with the use of photochromic substances (aggregates, host-guest, and polymer systems, solid nanoparticles) aswell as core-shell photochromic nanostructures based on polymers, silica, quantum dots, doped upconversion nanocrystals, and Ag, Au, etc. nanoparticles have been reviewed.

This review covers investigations of spiropyran iodides with N-substituted indoline fragment, and with the pyran cycle being annelated to N-methylated pyridine ring. The schemes of synthesis of iodides and their neutral precursors, as well as results of X-ray analysis and photochemical study of the crystals of the obtained compounds are presented. Based on our and literature data, the relationship between the structure and photochromic properties has been discussed for a series of salts and neutral pyridospiropyrans.

The effect of incorporation of plasmonic gold (Au) nanoparticle at the interface between transparent front electrode and hole transporting layer of molybdenum trioxide is studied using bulk heterojunction organic photovoltaic cells (OPVs) of poly-3- hexylthiophene and phenyl-C 61 -butyric acid methyl ester (P3HT:PC61BM) fabricated in ambient air condition as a model system. The current-voltage measurement of ITO/MoO3/P 3 HT:PC 61 BM/Al and Au incorporated OPVs under AM1.5G light of intensity 1 Sun showed 16% increase in short circuit current density (J SC ) and a 25% improvement in power conversion efficiency (PCE) with the incorporation of Au nanoparticles. The external quantum efficiency (EQE) measurement showed values varying from 40% to 60% over a wavelength range 350 nm to 700 nm with EQE enhancement over a broad spectral window. Scanning electron microscope studies were used to study the morphology of the Au nanoparticles made.

We present the description of the synthesis and characteristics of the SnO 2 and ZnO modified by novel tetrathiafulvalene (TTF) derivative. The analysis of the gas sensor properties showed the possibility of light photoactivation of modified semiconductor gas sensor due to the electron transfer from LUMO of TTF molecule to the conduction band of semiconductor matrix.

Three types of bichromophoric styrylquinoline (SQ) dyads are discussed in the review: bisstyrylquinoline dyads, styrylquinoline-merocyanine dyads, and styrylquinoline-naphthol dyads, in comparison with the corresponding model monochromophoric compounds. A variety of photochemical and photophysical processes is observed in the dyads: photoluminescence, reversible and kinetic-driven one-way photoisomerization, [2+2]photocycloaddition with formation of a single rctt-isomer of the cyclobutane derivative, Forster resonance energy transfer (FRET) where the SQ chromophore can act as an energy donor or acceptor. Operation of the dyads as photoswitches and molecular logic gates is also considered.

The photoconductive, photorefractive and nonlinear optical properties of composites from polyvinylcarbazole or aromatic polyimide containing supramolecular ensembles of (tetra-15-crown-5) - phthalocyaninato gallium, indium, - phthalocyaninateacetato yttrium, - phthalocyaninato ruthenium with axially coordinated pyrazine molecules were investigated at 633, 1030 and 1064nmusing continuous and pulsed lasers. Supramolecular ensembles (SE) were prepared through dissolution of molecular metallophthalocyanines in tetrachloroethane (TCE) and subsequent treatment via three cycles of heating to 90∘C and slow cooling to room temperature. The zscan method in femtosecond and nanosecond regimeswas used for measuring nonlinear optical properties phthalocyaninato indium and yttrium in TCE solutions and polymer films. It was established that effect of heavy metallic atom is basic factor which determines the quantum yield, photorefractive amplification of laser object beam, dielectric susceptibility of third order and nonlinear optical properties of metallophthalocyanines.

Full characterization of nanostructured organosilicon luminophores NOL4 and NOL5 based on the donor 2,2’-bithiophene and acceptor 1,4-bis(2,2′- bithiophene-5-yl)benzene units in dilute solutions and thin films by UV-Vis spectroscopy, DSC, TGA and X-ray techniques was reported. It was found that usage of these molecules as dopants (10–20 wt%) to the electroactive polyfluorene host in organic light-emitting devices (OLEDs) leads to the efficient spectral long wavelength shifting of the electroluminescence and an increase of the OLED performance as compared to the devices based on pristine polyfluorene, NOL4 and NOL5.

Optical and photoelectric properties of modern photosensitive polymers are of great interest due to their prospects for photovoltaic applications. In particular, an investigation of absorption and photoconductivity edge of these materials could provide valuable information. For these purpose we applied the constant photocurrent method which has proved its efficiency for inorganic materials. PCDTBT and PTB7 polymers were used as objects for the study as well as their blends with a fullerene derivative PC71BM. The measurements by constant photocurrent method (CPM) show that formation of bulk heterojunction (BHJ) in the blends increases photoconductivity and results in a redshift of the photocurrent edge in the doped polymers compared with that in the neat polymers. Obtained from CPM data, spectral dependences of absorption coefficient were approximated using Gaussian distribution of density-of-states within HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) bands. The approximation procedure allowed us to evaluate rather optical than electrical bandgaps for the studied materials. Moreover, spectra of polymer:PC71BM blends were fitted well by the sum of two Gaussian peaks which reveal both the transitions within the polymer and the transitions involving charge transfer states at the donor-acceptor interface in the BHJ.

In the present review we highlight the main research activities in the field of organic photonics and photovoltaics at the Institute for Problems of Chemical Physics of Russian Academy of Sciences (IPCP RAS). Extensive investigation of optical and electrical properties of π-conjugated organic compounds performed at IPCP RAS since 1960’s resulted in design of many exciting materials representing organic semiconductors, metals and superconductors. Organic Schottky barrier and p/n junction photovoltaic devices constructed at IPCP RAS in 1960’s and 1970’s were among the first examples of reasonably efficient organic solar cells at that time. These early discoveries inspired younger generations of the researchers to continue the work of their mentors and explore the world of organic materials and photonic devices such as molecular photonic switches, organic light emitting diodes, solar cells, photodetectors, photoswitchable organic field-effect transistors and memory elements.