“We evaluated the performance of a semi-empirical method much used in past decades but more recently neglected by the scientific community owing to its approximative nature. Using this method, we were able to reduce calculation time to four hours in a conventional computer. The low computing cost enabled us to consider a large statistical sample for simulations of molecules in solutions, which isn’t feasible with the currently hegemonic method,” Ramos told Agência FAPESP.

Since then, I have made a 4X speed box with 45 strips crammed as close together as I could get them. It required a 500W transformer, but the result is a unit that exposes a palladium print in 70 seconds!

These will be durable long-lasting exposure units that are professional-looking and durable. You also will have the benefit of your total understanding of their operation - after all, you will be building it! They are not cheap, but will be far cheaper than buying a ready-to-go unit of similar quality. This will come at the expense of a day or two of your time in putting it together. Please let me know if you are interested, and if we have enough people, we will get the process going.

Here it may be useful to examine the difference between one- and two-photon absorption. The general principle is that molecules absorb photons only when they can assume excited states that are compatible with the energy of the photons. The selection rules for one-photon absorption are not the same as for two-photon absorption, so that excited states prohibited for the former may be permitted for the latter. Owing to this difference, plus the high spatial resolution of excitation by two photons resulting from its non-linear optical nature, molecules that can absorb two photons are suitable for much more refined uses.

Ramos obtained a PhD in 2020 at the University of São Paulo’s Physics Institute (IF-USP) in Brazil, with a scholarship from FAPESP. He is currently a researcher with the National Fund for Scientific Research (F.R.S.-FNRS) at the University of Namur in Belgium.

To overcome this difficulty, an alternative method of calculation has been proposed by physicist Tárcius Nascimento Ramos and collaborators in an article published in The Journal of Chemical Physics (JCP).

Here it may be useful to examine the difference between one- and two-photon absorption. The general principle is that molecules absorb photons only when they can assume excited states that are compatible with the energy of the photons. The selection rules for one-photon absorption are not the same as for two-photon absorption, so that excited states prohibited for the former may be permitted for the latter. Owing to this difference, plus the high spatial resolution of excitation by two photons resulting from its non-linear optical nature, molecules that can absorb two photons are suitable for much more refined uses.

As I mentioned above, I will provide with the boxes a complete set of instructions on how to wire them together. It is not complicated, and can be easily accomplished by anyone reasonably adept with using a few hand tools, namely a wire-stripper, screwdriver and pliers. While soldering is not required, I do recommend soldering several of the pigtail connections that are needed just to ensure the durability of the connection.

Computer modeling of two-photon absorption by organic molecules in solution was the subject of Ramos’s PhD research. The JCP article refers to another step forward in this investigation.

The practicality of this method can be sensed by taking into consideration the fact that the molecule studied, which is derived from stilbene, has more than 200 atoms (of carbon, oxygen and hydrogen). Besides the number of components, which alone would make conventional simulations extremely laborious and expensive, these large molecules have an additional complication: they are flexible, and their electronic properties change when they change shape (by twisting, for example).

An alternative method proposed by a Brazilian physicist cuts the time for computer simulation of the absorption spectrum from two days to a few hours.

“We evaluated the performance of a semi-empirical method much used in past decades but more recently neglected by the scientific community owing to its approximative nature. Using this method, we were able to reduce calculation time to four hours in a conventional computer. The low computing cost enabled us to consider a large statistical sample for simulations of molecules in solutions, which isn’t feasible with the currently hegemonic method,” Ramos told Agência FAPESP.

Molecules with a high probability of simultaneously absorbing two photons of low-energy light have a wide array of applications: in molecular probes for high-resolution microscopy, as a substrate for data storage in dense three-dimensional structures, or as vectors in medicinal treatments, for example.

The new box with 11mm strip spacing using the Inkjet Mall Type 2 strips will expose a pt/pd print in about 4 minutes. If you choose to upsize the transformer and go with a denser strip spacing the exposure times will of course go down. I am attaching pictures of the finished prototype so you can get a sense if this is something you might want to take on. The total size is 20”x30”. The illumination area is 18” x 24”. The weight is 14.5 pounds.

To get the cost benefits of bulk ordering, there must be a deadline for ordering the aluminum enclosures. In order to give everyone plenty of time to make a decision, we have arbitrarily picked three dates during the year as deadlines. The boxes will require about two weeks to fabricate and ship to my location. I will do the basic assembly of the box, which involves riveting on the rear panel and riveting on the hinge that attaches the door. What you will receive is a empty box with a Borg relay timer, ready for you to attach the remaining components.

By José Tadeu Arantes  |  Agência FAPESP – Absorption spectroscopy is an analytical chemistry tool that can determine if a particular substance is present in a sample by measuring the intensity of the light absorbed as a function of wavelength. Measuring the absorbance of an atom or molecule can provide important information about electronic structure, quantum state, sample concentration, phase changes or composition changes, among other variables, including interaction with other molecules and possible technological applications.

Ramos obtained a PhD in 2020 at the University of São Paulo’s Physics Institute (IF-USP) in Brazil, with a scholarship from FAPESP. He is currently a researcher with the National Fund for Scientific Research (F.R.S.-FNRS) at the University of Namur in Belgium.

Molecules with a high probability of simultaneously absorbing two photons of low-energy light have a wide array of applications: in molecular probes for high-resolution microscopy, as a substrate for data storage in dense three-dimensional structures, or as vectors in medicinal treatments, for example.

“At the end of the study, we bridged the experimental gap by characterizing at the microscopic level the one- and two-photon absorption spectra for this class of molecules. We found that the semi-empirical method we tested, often neglected owing to its approximative nature, is the most suitable for predicting the one- and two-photon absorption spectra of large molecules in solution. This finding points to a route for molecular engineers to develop novel compounds with greater efficiency in their various application branches,” Ramos said.

The link below leads to a download page with a new calibration workflow for polymer plates photogravure for printmakers using the QuadToneRIP printing software. The workflow enables the user to...

Studying the phenomenon by means of direct experimentation is difficult, however, and computer simulation usually complements spectroscopic characterization. Simulation also provides a microscopic view that is hard to obtain in experiments. The problem is that simulations involving relatively large molecules require several days of processing by supercomputers or months by conventional computers.

“Microscope imaging with two-photon absorption has far higher resolution and can be used to characterize deep tissue with less damage to the surrounding structures. In the case of data storage, the high resolution means 3D structures can be created with precision and plenty of detail, so that points inside materials can be encoded with high data density per volume,” Ramos explained.

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The currently hegemonic method is density functional theory (DFT), a mathematical tool widely used in quantum mechanics to describe the electronic properties of complex systems without having to investigate the individual wave functions of each electron.

The cost of having these aluminum enclosures fabricated goes down as more units are added to an order. The single box cost typically has about 50% of the total cost in set-up charges. If more boxes are ordered at one time, set-up charges can be spread out over more units. Thus, it is more economical to place an order for 5 boxes than for a single box.

“At the end of the study, we bridged the experimental gap by characterizing at the microscopic level the one- and two-photon absorption spectra for this class of molecules. We found that the semi-empirical method we tested, often neglected owing to its approximative nature, is the most suitable for predicting the one- and two-photon absorption spectra of large molecules in solution. This finding points to a route for molecular engineers to develop novel compounds with greater efficiency in their various application branches,” Ramos said.

Computer modeling of two-photon absorption by organic molecules in solution was the subject of Ramos’s PhD research. The JCP article refers to another step forward in this investigation.

We now offer a product that is a box and timer module in combination with written and video instructions on how to assemble them.

The article “Calculation of the one- and two-photon absorption spectra of water-soluble stilbene derivatives using a multiscale QM/MM approach” is at: pubs.aip.org/aip/jcp/article-abstract/159/2/024309/2902110/Calculation-of-the-one-and-two-photon-absorption?redirectedFrom=fulltext.

An alternative method proposed by a Brazilian physicist cuts the time for computer simulation of the absorption spectrum from two days to a few hours.

“The alternative method we used was INDO/S [intermediate neglect of differential overlap with spectroscopic parameterization]. It’s based on the wave function of the molecular system but resolves approximately. Parts of the complex and computationally costly calculations are replaced by tabulated values obtained by adjusting experimental spectroscopic data. This makes the method highly efficient for theoretical studies of large molecular compounds,” Ramos explained.

By José Tadeu Arantes  |  Agência FAPESP – Absorption spectroscopy is an analytical chemistry tool that can determine if a particular substance is present in a sample by measuring the intensity of the light absorbed as a function of wavelength. Measuring the absorbance of an atom or molecule can provide important information about electronic structure, quantum state, sample concentration, phase changes or composition changes, among other variables, including interaction with other molecules and possible technological applications.

“Microscope imaging with two-photon absorption has far higher resolution and can be used to characterize deep tissue with less damage to the surrounding structures. In the case of data storage, the high resolution means 3D structures can be created with precision and plenty of detail, so that points inside materials can be encoded with high data density per volume,” Ramos explained.

Besides the doctoral scholarship awarded to Ramos, the study was supported by FAPESP via two other projects (14/50983-3 and 15/20032-0). The co-authors are Sylvio Canuto (last author, IF-USP), Daniel Luiz da Silva (Federal University of São Carlos, UFSCar, Brazil), and Leandro Franco (Karlstad University, Sweden).

I have had a lot of interest expressed by workshop participants in the UV-LED exposure units I have built over the last two years. These exposure boxes are designs that I have had fabricated in heavy-duty 3/32” 5052 aluminum.

The currently hegemonic method is density functional theory (DFT), a mathematical tool widely used in quantum mechanics to describe the electronic properties of complex systems without having to investigate the individual wave functions of each electron.

To overcome this difficulty, an alternative method of calculation has been proposed by physicist Tárcius Nascimento Ramos and collaborators in an article published in The Journal of Chemical Physics (JCP).

Here are a few photos of the prototype box I built with 24 strips of the Inkjet Mall UV-LEDs spaced at 11mm. It will expose a palladium print in 3-4 minutes.

Studying the phenomenon by means of direct experimentation is difficult, however, and computer simulation usually complements spectroscopic characterization. Simulation also provides a microscopic view that is hard to obtain in experiments. The problem is that simulations involving relatively large molecules require several days of processing by supercomputers or months by conventional computers.

The practicality of this method can be sensed by taking into consideration the fact that the molecule studied, which is derived from stilbene, has more than 200 atoms (of carbon, oxygen and hydrogen). Besides the number of components, which alone would make conventional simulations extremely laborious and expensive, these large molecules have an additional complication: they are flexible, and their electronic properties change when they change shape (by twisting, for example).

Besides the doctoral scholarship awarded to Ramos, the study was supported by FAPESP via two other projects (14/50983-3 and 15/20032-0). The co-authors are Sylvio Canuto (last author, IF-USP), Daniel Luiz da Silva (Federal University of São Carlos, UFSCar, Brazil), and Leandro Franco (Karlstad University, Sweden).

“The alternative method we used was INDO/S [intermediate neglect of differential overlap with spectroscopic parameterization]. It’s based on the wave function of the molecular system but resolves approximately. Parts of the complex and computationally costly calculations are replaced by tabulated values obtained by adjusting experimental spectroscopic data. This makes the method highly efficient for theoretical studies of large molecular compounds,” Ramos explained.

The article “Calculation of the one- and two-photon absorption spectra of water-soluble stilbene derivatives using a multiscale QM/MM approach” is at: pubs.aip.org/aip/jcp/article-abstract/159/2/024309/2902110/Calculation-of-the-one-and-two-photon-absorption?redirectedFrom=fulltext.