Questions related to Photophysics
I have a compound which I recently studied its photophysical properties. I have observed that when I use a non-polar medium, like DCM, the quantum yield is higher than when I use a polar medium like DMF. Moreover, the fluorescence lifetime is also nearly twice in non-polar medium than in the polar medium. What could be the prospective cause for this observation? Any possible suggestions?
I'm a PhD student in polymer physics particularly on photophysics of conjugated polymers. While reviewing literature I come across an article by Shu Hu and coworkers on 'Effect of Thermal Annealing on Conformation of MEH-PPV Chains in Polymer Matrix: Coexistence of H- and J-Aggregates' in which they assign the emission peak (I00) of H-type aggregates at lower energy than J-type aggregate when they coexist, which, I think, contradicts Kasha theory.
Some body help me explain this.
I have synthesized a compound which is pure as well as no other possible diastereomers are present in it, as evident from ¹H NMR. On inspection of its photophysical properties an anomaly was noted as described below:
- when the compound was excited in the region (~400 - 450 nm) of its highest absorbance a low intensity emission peak was observed at about 500-550 nm with indication of excimer like entity formation (600 - 650 nm) on varying the concentrations.
- On the other hand , excitation of the molecule at a peak of lower absorbance, near to the λmax around 350 nm a very high intensity and sharp single emission peak was observed around 380 nm with no excimer like entity at higher concentrations.
What could be the plausible reasons behind these observations?
I would be grateful for valued suggestions, if any.
I know that transition metal complexes have attractive photophysical properties. But, Why pepole mostly working with Ruthenium. Secondly, How ligand affect the specificity to organelles.
Moreover, how we can say that this kind of ligand with metal specific to Mitochondria or lysosomes etc.
I am trying to model the reaction of triplet oxygen with organics. The reaction starts as a triplet overall, but I believe it would end as two doublets at infinite separation (HOO and an organic radical), which might further react to give a singlet. Clearly the spin is not being conserved, so I think I'm missing some important point. I have modelled this using HF, B3LYP, and MP2 to start.
My experience is predominantly in closed -shell inorganic species. Are there some key references that I should consult? My hunch is that there is some "photophysical" process like intersystem crossing that I will need to model.
Hi, can anyone discuss how to do multivariate curve resolution for the transient absorption spectra of bulk heterojunction organic solar cells? Thank you in advance.
I am working on making nanocomposites from silicon nanocrystals and thiolate. I get a massive change in the photophysical properties of some composites. However, other composites did not show me any change in photophysical properties. I hope anyone can go more in-depth and explain how the interaction between radical thiolate and the surface of silicon nanocrystals works. Let us focus on the chemistry point of view.
I appreciate your time in answering my question.
I have seen a number of publications state that organic radicals often exhibit quenched photo-luminescence, yet offer no explanation as to why. Can someone offer a physical explanation as to why this would be the case? This question is particularly puzzling to me as you can clearly see polaronic or excitonic absorption bands in an absorption spectrum corresponding to the excitation of the radical anion. Why then does it not luminesce when excited at these wavelengths?
i need to know, why there is an red shift in linear absorbance spectra as it measured from different solvents (Methanol,acetone and DMF). is is due to polarity of solvents? or any other kind of reasons?
I am relatively a newcomer to the amazing fields of photophysics and photochemistry.
From the available scientific literature, we may read that induced chlorophyll a fluorescence is mainly emitted by chlorophyll a molecules, located in Photosystem II (PSII), upon illumination onset. It has been reported about 300-500 chlorophyll a molecules in a single Photosystem II.
PSI fluorescence is constant and much lower than fluorescence from PSII. Its contribution to emitted plant fluorescence is considered negligible.
Some authors speak about P680 (a pigment named P680, located in Photosystem II), the reaction center RC or the special pair or the special chlorophyll dimers pigments PD1 or PD2, as the only source of fluorescence. I have a bit of confusion because it is not clear what chemical species is emitting the fluorescence that we can sense with our portable fluorometers.
1) If the Special Pair or RC is closed (it has been chemically switched to its reduced state), during the time that the Special pair is in that state, is the full bunch of chlorophyll a molecules in PSII going to dissipate their excitonic energy as fluorescence?
2) Why fluorescence emitted from PSI is not variable but constant? Does it has this fact something to do with the ratio [Chl a] to [Chl b] ???
Thank you so much in advance for your precious and kind help!
The recoil force of radiation is known for spontaneous emission (for the radiation of an accelerating charge or dipole), when the photon field is empty. Is there any difference when stimulated emission is considered? Would it be enough to add an external force to the original radiative reaction-force without changing the original form of the radiative reaction?
What will be the sign of zeta potential for amine functionalized nanoparticles? The amines are neutral (not protonated). Due to the electron rich character of amine functional group shall I expect net negative charge?
Did anyone observe the suppression of low fluorescence signals from one organelle due to high signals from other organelles?
We are working on the photophysical and electrochemical properties of some acridinedione derivatives. The dyes are acts as very good electron acceptor in its excited state. So, we are interested to determine the reduction potential of the dyes. When performing cyclic voltammetry, I was unable to observe the reduction peak but the reduction potential of the same dye was reported using pulse radiolysis technique.
Can there be a system which undergo reduction but the corresponding process is not observable in cyclic voltammetry? What may be the possible reasons for this phenomena?
Please anyone explain.
Photophysical studies of a molecule which is under development was done by using uv-vis spectoscopy. By inctreasing concentration gradually, the intensity of one of the signal was observed. This falls under the category of "hyperchromic shift". In literature, bathochromic (for J-aggregation) and hypsochromic (for H-aggregation) are well known. But hyperchromic shifts are not well documented.
Can Hyperchromic shift cause these type of agglomerations also?
I want to get some information about spin-forbidden phosphorescence emission.
Some articles say that strong spin-orbit coupling would mix triplet and singlet energy and increase the ISC (intersystem crossing). What is the result of mixing triplet and singlet energy? How this mix promote the triplet excited state deactivating through phosphorescence?
Thank you in advance!
I used Rhodamine B to find the quantum yield of pyrene, but I got it wrong. I was reading some literature and it says that reference dye should resemble your dye ( expected QY and absorption band).
And I am also trying to find the quantum yield of benzopyrene.
i cant find a reliable source explaining the consequences of the sulfonate modifications in alexa fluor dyes. why does the modification lead to an increase in brightness?
Thank you for your answer.
Hi everybody I have the following questions. It would be very nice if some of you could help understanding them.
1. What is the significance of chi-square in life time measurement?. Why should the value be lower than 1.2 if it has to be acceptable data? or can it be higher also depending upon the system under consideration, say for example aggregated species.
2. Why do the organic aggregates (say organic compound dissolved in THF and added to water to get the dispersion) give multiple decay values (for example 2 or 3) in the lifetime measurements?
I am not able to locate any reference where aminocoumarins have been studied at low temperatures in non-polar solvents?
Hi all. I'm doing some TIRF analysis of lipid membranes and layers, with and without dyes. I've long been pondering about some "strange" phenomena I've encountered. The internet isn't much help. It seems TIRF in practice is a closely guarded secret...
When I excite my sample (could be anything, even something that shouldn't fluoresce at all!) at either 488 nm or 640 nm, I get two very different results. At 488 I get a hazy outline of the sample morphology. However, if I excite with 640 I get a myriad of vibrating, glowing spots, as if I'm inducing fluorescence in a small % of the molecules (although there aren't any obviously fluorescent compounds involved). The density of the spots also roughly correlates with the surface morphology. Why does this happen?
And secondly, why are small impurities on the surface so extremely bright? Does it have something to do with the way it interacts with the light?
And finally, how come I can excite the dye Atto655 perfectly well with low intensity at 488 nm, although spectra suggest that it's impossible? Is there some configuration with the microscope I'm overlooking (aside from using the wrong laser entirely. But I'm pretty sure I'm not. It looks pretty blue to my eyes)?
All solvents and samples are of highest purity grade, and equipment strictly cleaned and used for specific purposes only to avoid any type of contamination.
I have got the enhancement of UV/VIS value (RTPL emission at 380 nm/550 nm) (from 2.2 to 9.5) for sol-gel derived doped zinc oxide thin films. What might be the possible explanations?
I got a tough question concerning the pile-up effect of TCSPC technique.
As a book says, pile-up effects result from the fact that a TCSPC device can detect only one photon per signal period. If the detection rate is so high that the detection of a second photon within the recorded time interval becomes likely the signal waveform is distorted.
There is a strange words for me that the second photon could be probably detected within a pulse period if the detection rate is high enough. I wonder how it could happen if we set an upper threshold for TAC that can only detect one photon.
The size obtained from TEM of Carbon Dots are the size of carbon core alone or it includes the length of surface functionalization too?
Looking back on about 30y of femtosecond optics and spectroscopy, I would like to start a discussion on which achievements active researchers today consider as, e.g. most valuable, as a break-through, most visionary etc. To be specific, I'm not looking for top-ranked papers but a more general idea/concept/invention/technique/method that has in your opinion revolutionalized the field, has paved the way for succeeding studies and/or has been picked up by other branches / has inspired researchers in other fields such as biology, chemistry or even industry.
Measured excited state life time for terephthalic acid (2.4 ns) and 2-hdyroxyl terephthalic acid (7.6ns) by TCSPC method in acetonitrile which was obtained after monoexponential fitting of the decay curve. I was wondering how hydroxy group can stabilize the excited state?
Is it possible to quantify and to follow the transformations of the iron-oxalate complex under UV irradiation? Photo-Fenton-like system
On what basis these are different? Do same applied to GSOP ( ground state oxidation potential) and HOMO level of a molecule?
UV-Stabilizers are very useful additive for engineering thermoplastics. Since 1164, goes through well studies ESIPT (excited state intramolecular proton transfer) where as 3638 do not have adjacent -OH group to go through this mechanism. Please see attached structure and uv absorption profile. 3638 shows fluorescence where as 1164 is very very little. Any suggestion on understanding the working mechanism of 3638 will be highly appreciated.
When a phosphorescence emission occurs, Singlet spin state is converted to triplet spin state and when it comes to ground state after phosphorescence emission of energy it again in singlet state-----What is the driving force for such spin inversion ?
I made some perovskite solar cells with ZnO as ETL, P3HT as HTL and gold as the back contact. Then I wanted to store them for longer period outside the glove box, So, I encapsulated them with UV curable optical cement and a glass slide and used black UV light for the curing. But when I stored the cells out side the glove box for 24 hours, their efficiency decreased significantly. If anyone will please advise me what to do here.
The optical resin I used is NOA81 and more information for it is in the link: http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=196&pn=NOA68&gclid=Cj0KEQjwyMafBRCU7OCRyc2vitsBEiQAKV4H9M-R7b2rgVM1XVChHNeFoHdnqpbHgvm2_PUD7Lj_byAaAq4_8P8HAQ
Most of the literature search for me result into hits which are either done in 1970's or late 80's. I am interested mainly in knowing about transient absorption and photophysical nature singlet, triplet, luminescence etc. Sharing any useful literature will also be highly appreciated.
I measured the Nano-second transient absorption spectroscopy and singlet oxygen emission for a terephthalate based system (attached), in ACN it shows weak fluorescence emission intensity, strong triplet-triplet transient absorption (lifetime in micro second) and strong singlet oxygen emission as well. Same systems in toluene, shows strong fluorescence emission but no triplet-triplet absorption and singlet oxygen emission, i was wondering what might be possibly leading to such a different behavior in these two solvents?
Suppose I reverse bias my solar cell diode and measure external quantum efficiency as a function of applied reverse bias. Then the EQE is increasing with the applied reverse bias. After certain reverse bias the EQE is not changed very significantly? Can I get any idea regarding interface traps from the reverse bias dependent EQE for my device?
Sometimes I get a strong PL peak for my Methyl ammonium lead iodide perovskite samples around 770nm and sometimes I don't get anything at all. All my samples are prepared using the same precursors and prepared with the same method and looked exactly the same. Also, they all were excited at 532 nm.
e.g. one attached Fig. 1 (broad) vs. Fig. 2 (slightly sharp) does it tell anything about nature of triplet state? it was measured by using Laser Flash Photolysis nanosecond transient absorption (LP 920, Edinburgh instruments)
I am stuying the photophysics of a system based on CdSe QD, and a cyanine dye , cardiogreen, CG.
Till now we have some preliminary results , let me resume :
When we have the pure dye in a meOH solution, and we use an excitation source at 530nm, we dont see any emission from the dye .
as soon as we start adding QD to the same solution, we start to see an accumulation of both signals, one of the QD and the other of CG
Then , we probe also, the quenching of the PL by adding CG, and we have a big decrease on the steady state emission signal. With 1 equivalent CG:QD we have 40 % of quqenching of PL intensity , at 5 eq , the quenching is close to 95%.
At the same time that we perfomr these experiments we measure the TCSPC histograms. We start with the pure QD and the PL lifetime is around 20ns. As soon as we start to ad CG, the lifetime is decreased, but the relative change is not as big as the Intensity decrease. I mean 1 eq is just 8 % of change ion the lifetime, and when we reach the 5 eq , we have at most 40 %
We propose that we could have a competitive mechanism which happends before the emissive state is formed, which is responsable for decrease the total amount of emmissive state formed, this would lead to a decrease in the Intensity of the PL .
We have propose the idea of haviong an energy tranfer or an electron transfer process from one of the higher excitonic states of the quantum dots.
However how can we probe either one or the other?
I am now performming experiments on tour femtosecond fluorescence up conversion technique , an dmy idea is to measure the Internal Conversion time that Glaasbek (JPC C 2006. 10.1021/jp055795g) has measured before
AND SEE WHAT HAPPENDS TO THE RISE TIME OF THE EMMISSIVE STATE WHEN WE ADD CG.
Even we see afaster rise time due to the presence of CG, still we can not decide if we have energy transfer or electron transfer.
So I ask again tricks and tips to discriminate between these two phenomena?
Thanks for you contributions
Pedro Navarro PhD
The Commercially available Ti-Nanoxide-HT from solaronix brand containing an organic binder. If we use it for quenching studies, will the binder influence our result? What I am thinking is that we are coating the Ti-Nanoxide-HT (containing the binder) on FTO or on glass plate either by using doctor blade or spin coating method followed by annealing. After sensitizing it we are carrying out thin film photophysical studies. For investigation of solution state photophysical properties between the sensitizer and the nanoxide it is logic to use the same material i.e. with binder. It should be the actual condition. Am I right? Please give me your suggestions.
Decay time of a molecule having charge transfer character shows decrease in life time with increasing amount of water in THF/Water system. Quantum yield also decrease along with red shift. But the molecule shows longer decay time with increasing solvent polarity (Tol.<DCM<DMSO) along with red shift and decrease in quantum yield.
I have a FRET sample that shows expected fluorescence when the sample is stored in 2mL eppendorf tubes (Fisherbrand 05-408-138). However, the fluorescence intensity drops drastically and immediately when the samples are transferred to 0.5mL tubes (Fisherbrand 02-681-311). Both were sterilized using the same autoclave procedure. According to the company website, the 2mL tubes are DNase and RNase free but the 0.5mL ones are not. I was under the impression that autoclaving took care of contaminations.
Does anyone know what's going on? I have a ton of 0.5mL tubes so would like to avoid buying a different kind if I can.
In the photophysical discussion of the UV-vis spectra of reported phosphorescent iridium complexs for OLEDs, the absorption bands are commonly divided into to "two major absorption bands". Absorption bands with high absorbance are usually ascribed to the absorption of ligand-centered transition, such as pi-pi* transition. And absorption bands with lower absorbance are usually correlated to the spin-forbidden metal-to-ligand charge transer transition. This kind of correlation is overly simplified. I want to know how can I correlate the absorption bands more detail? Also, how can I distinguish the pi-pi* transiton with charge transfer transition of the ligands if they are both possible to happen?
How to measure the efficiency of Dexter Energy Transfer? Is there a way by fluorescence decays?
While in photophysical (absorption and emission) studies I found that the rhodamine derivatives towards metal ions chemosensing was more favorable in acetonitrile solution and not in other solvent such as DMF, DMSO etc. what's the reason behind this?
The sample has strong luminescence around 630nm in solution while no stimulated emissions were detected in the femtosecond transient absorption spectra during the whole measurement. Is there any other possible origins besides overlap between ESAs and stimulated emissions?
I observed continuous redshift of the PL emission spectra while increasing the excitation wavelength of semiconductor polydisperse QD. I would like to understand the underlying physics responsible for this redshift? How does increase in excitation causes redshift in NP?
This is quite a specific question, I know. I'm currently determining the absorption coefficients of a range of fluorescent materials and am a bit stuck with this one because I can't find its molecular weight anywhere. From literature I know Lumogen F Red 305 has Mw = 963.956 and Lumogen F Orange 240 has Mw = 710.873. It is necessary to know these so that the molar concentration can be determined which is essential in applying the Beer-Lambert law to determine the extinction coefficient. I've emailed BASF but the lumbering giant hasn't registered my existence.
Is this something that can be replaced manually or do I just have to accept that this is the window provided for the PMT I'm using (UV-transmitting glass on an R446)?
I could employ more filters to block out as much light as possible but I was just wondering if this approach is possible.
A blue shift of the emission peak of my compound upon the addition of quencher was observed. I guess there is an electron transfer between it and quencher. But I don't know how to explain this blue shift. Anybody could give me some suggestions?
P.S.: There is no change in UV absorbance curve of the compound upon addition of quencher.
I have labeled a protein with Cy3B and immobilized it on a surface. I chose the dye over Cy3 because of its higher brigthness. However, I get fast photobleaching and cannot detect as many photons from my molecule as the people in the literature get with a regular Cy3 dye. Photoprotection and laser power are already optimized.
So, my question: is there an inherent difference in photostability (meaning the number of photons you can get out of a single dye molecule before it bleaches) between the two dyes?
I have not found any article reproducing the results reported by:
B. Oliveira dos Santos, C. E. Fellows, J. B. de Oliveira e Souza, and C. A. Massone
“A 3% Efficiency Nitrogen Laser”
Applied Physics B (Photophysics and Laser Chemistry) 41 (1986), pp. 241-244
If anybody knows about this please, let me know!
In our laboratory we built a laser according to these specifications but we never reached the claimed 3% efficiency. We obtained only a 0.11% efficiency (Revista Mexicana de Fisica, 37(3), (1991) pp 391-395)
Latter on we used that laser to build a MOPA system :
Thanks for any information!
The Lippert-Mataga equation (see attached image) describes how the stokes shift changes as a function of solvent properties (epsilon and n) and the fluorescent molecule properties (dipole moments and Onsager radius, a). I can't see how this equation deals with the blueshifts that can occur in solvation phenomenon in which energy is essentially given to the singlet state, before fluorescence occurs, by an interaction with the host medium. Can someone explain this to me?
(In the equation the LHS is Stoke's shift in wavenumbers, on the RHS epsilon is relative permittivity, n is refractive index, mu is dipole moment with subscript E = excited state and G = ground state, a is the Onsager radius and C is a constant equal to the unperturbed Stoke's shift in vacuum).
Absorption spectra of complexes could be classified either ligand-center pi-pi (LC), metal-to-ligand charge transfer (MLCT), or ligand-to-metal charge transfer (LMCT). In most cases, LC band is easily to assigned, but the assignment of MLCT and LMCT is sometimes confusing. TDDFT method might be a good approach, but is there other methods to give a better assignment?
I just got a weird, broadened emission band for my poly-ala-helix (21 residues incl. some arginines for solubility) which has two labels (Xanthone and Naphtaline) that I'm using for triplet-triplet-energy transfer (TTET, similar to FRET, but different). The labels are attached on the 10th and 12th positions, which means they are facing different sides of the helix and can not attach to each other in the folded state. At 7M urea the unfolded state is stronger populated and the interaction is more likely and will also stabilize the unfolded state. This is why I expected dimer formation at 7M urea.
Well, this is the spectrum that I got and - according to literature - this seems to be an excited dimer. What should the spectrum look like for a regular dimer? How can I if show it's one or the other? Is this spectrum already proof enough?
Is there any explanation if I observe only (or mainly) the decay in fluorescence as opposed to absorbance?