In signal processing one often faces the phase problem, i.e., when an image is formed information about the phase is lost so that only information about intensity is available. This is often an issue in astronomy, biology, crystallography, speckle imaging, diffractive imaging where the phase of the object must be known. While there have been many approaches how to find a solution to the phase problem, numerical algorithms recovering the phase from intensity measurements become more and more popular. One of such algorithms called PhaseLift has been recently proposed. In this study, we show that even 4 masks may be sufficient for reasonable recovery of the phase. The original wavefront and the recovered wavefront were visually indistinguishable and showed very high correlation. In addition, the four masks are essentially one and the same mask rotated around in steps of 90 degrees. By using just four rotated versions of a single mask, the PhaseLift could be easily implemented in real optical systems thus simplifying the wavefront sensing in astronomy, biology etc.
Organic materials are becoming more popular due to their potential application in electronics. Low molecular weight materials possible produce from solution are in special consideration. It gives the possibility to avoid both thermal evaporation in vacuum, and use of polymers in thin film preparation process. Indandione fragment containing azobenzene compounds are one of such materials. These compounds are good candidates for use in design of novel molecular electronic devices due to their possibility to form amorphous structure from solution thus allowing developing flexible, small size systems with low production costs. In this work three indandione fragment containing azobenzene compounds were investigated. Difference between these compounds is bulky groups which assist formation of amorphous thin film. Absorption spectra of the investigated compounds are similar to P3HT but with higher absorption coefficient. Molecule ionization and electron affinity levels of these compounds are around -5.45eV and -3.80eV, respectively. Combining PCBM with investigated compounds could lead to difference between electron affinity levels maximum of 0.15eV. It is several times less compared to ~1eV for P3HT:PCBM system. Higher difference between the donor ionization level and the acceptor affinity level could also be obtained which should lead to the higher open circuit voltage.
Low molecular mass organic compounds which make thin films from volatile organic solutions would be great benefit in future
organic light emitting systems. Two most important advantages could be mentioned. First - the repetition of synthesis of small
molecules is better than for polymers. Second - wet casting methods could be used.
In this work we are presenting optical, electroluminescence and amplified spontaneous emission properties of four original glassy
forming compounds containing 2-tert-butyl-6-methyl-4H-pyran-4-ylidene fragment as backbone of the molecule. They has the same
N,N-dialkylamino electron donating group with incorporated bulky trityloxy ethyl groups. The difference of these compounds is in
electron acceptor group. One has 1H-indene-1,3(2H)-dione group, second has pyrimidine-2,4,6(1H,3H,5H)-trione group, third has
malononitrile group and fourth has 2-ethyl-2-cyanoacetate.
Absorption maximum of the compounds is between 420 and 500 nm and is red shifted from weaker acceptor group to stronger one.
The electroluminescence efficiency for simple device ITO/PEDOT:PSS/Organic compound/BaF/Al is low. For the best one with
malononitrile group it was 0.13 cd/A and 0.036 lm/W. It could be increased by optimising the sample geometry or adding addition
layers for charge carrier transport and exciton blocking. But nevertheless the use of these compounds in organic light emitting devices
in neat films is unlikely.
Attached bulky trityloxy ethyl groups and tert-butyl group decrease interaction between the molecules thus allowing to obtain
amplified spontaneous emission in neat thin films for all investigated compounds.