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Re^5: How to check for acceptance of Kasha's rule from TDDFT data...?

Ilya Ioffe
ioffe@thermo.chem.msu.ru


Dear Siddheshwar,

1) Kasha's rule is of kinetic nature. It suggests that radiationless relaxation from Sn to S1 (with further radiative decay to S0) is normally of higher probability than fluorescence directly from Sn. But nothing requires S1 to have higher oscillator strength.

2) ISTATE=x means that you are requesting properties for the excited state no. x and/or that you are optimizing it. The excitation energies and oscillator strengths are always reported between S0 and each of the excited states requested by NSTATE, not between the excited states (you would need a multiconfiguration method rather than TDDFT to compute that). If you'd like to calculate fluorescence energy from a particular relaxed Sx, optimize this very Sx.

Best regards,

Ilya



On Thu Sep 25 '14 2:18pm, Siddheshwar Chopra wrote
--------------------------------------------------
>Dear Pavlo,

>Please have a look at the energies for 3 excited states from absorption and emission runs:
>EMISSION CALCULATION:: ISTATE=1, NSTATE=3

> EXCITED STATE 1 ENERGY= -1355.7217994424 S = 0.0 SPACE SYM = A

> EXCITED STATE 2 ENERGY= -1355.6780193460 S = 0.0 SPACE SYM = A

> EXCITED STATE 3 ENERGY= -1355.6756729663 S = 0.0 SPACE SYM = A
>
>
>
>UV CALCULATION:::: ISTATE=1, NSTATE=3

> EXCITED STATE 1 ENERGY= -1355.7080939866 S = 0.0 SPACE SYM = A

> EXCITED STATE 2 ENERGY= -1355.6840777343 S = 0.0 SPACE SYM = A

> EXCITED STATE 3 ENERGY= -1355.6782292662 S = 0.0 SPACE SYM = A

>
> IN ALL THE TRANSITIONS... EXCITED STATE 1 HAS THE LOWEST ENERGY...BE IT ABSORPTION OR EMISSION...So for emission, if the initial state is S1,
>then what are these excited states? Ideally speaking in this run, S1 is the ground state. The excited state 1 has the lowest energy (-1355.7217994424). Then it should be the lowest vibrational level of S0.
>Please help me in this analysis.

>Kind Regards,

>On Thu Sep 25 '14 6:47am, Siddheshwar Chopra wrote
>--------------------------------------------------
>>Dear Pavlo,
>>That is some real relief... Actually the same under study is a doped one. Sir please read my last message and answer them. The picture of Emission process is unclear to me, with regard to the firefly calculations. The ISSTATE=1 is ENSURING that we are finding a transitions from S1 only..Is it correct?
>>So now SPECIFICALLY about the emission calculations::: What are these EXCITED STATE 1, 2 and so on (depending on NSTATE vaue)? I mean are these the S0 vibrational levels now (because now we are studying de-excitation)? If yes, then how exactly do I find the emission wavelength? Is the analysis similar to the absorption spectra analysis then? I mean using osc. str. etc.? Please guide me.
>>Also if Kasha's rule holds good, then do I get a high osc. str. at 1st excited state itself in the o/p file?

>>Regards,

>>On Thu Sep 25 '14 1:42am, Pavlo Solntsev wrote
>>----------------------------------------------
>>>Kasha's rule doesn't always work. For example, if you have redox active group near chromophore.

>>>Try to figure out absorbtion--emission situation for a porphyrin.

>>>-Pavlo.
>>>
>>>
>>>
>>>On Wed Sep 24 '14 9:11pm, Siddheshwar Chopra wrote
>>>--------------------------------------------------
>>>>Dear users,
>>>>Somebody please help me in understanding this concept. I need to know that by setting istate =1 in emission spectra calculation, I am actually setting or calculating the de-excitation from the S1 state. Am I correct? If yes, then the TDDFT o/p gives me a set of transitions possible for every excited state (set by variable nstate).What are these nstates now? Do they hold any significance in S1-->S0 transition? Do we mean that these are the vibrational levels of S0 level? Please explain this in the light of kasha's rule.
>>>>I am worried because I am unable to point out the emission wavelength. Please help me Alex Sir and Pavlo Sir. Please help me in analysing the emission calculations.

>>>>Kind Regards,
>>>>
>>>>
>>>>n Tue Sep 23 '14 12:21pm, Siddheshwar Chopra wrote
>>>>---------------------------------------------------
>>>>>Dear Users,
>>>>>Please have a look at the attached file which contains a table describing the contributions/transitions from first four states only for both the absorption and emission calculations. For absorption, I understand that the final state can be any of the excited states which has highest osc. strength. Am I right? But my doubt is regarding kasha's rule... If you see the emission data, the first excited state has a very low oscillator strength of 0.004 (HOMO-->LUMO(97 at 2678.9 nm. However the higher states have a better contribution than this state. So please tell me how to analyse this properly. To my knowledge emission wavelength is around 600-730nm.
>>>>>I would be grateful for any help.

>>>>>Kind Regards,


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