I wanted to know the range of pi-pi* and intramolecular charge transfer bands in the absorption spectrum of an organic dye (donor-spacer-acceptor).
In almost all cases charge transfer only occurs in the excited state and so the CT has no ground state absorption. Also, the 'ground state' of a CT state is disperse, it is unstable and relaxes back to the ground state of the separate donor acceptor system. So, unless the material is fairly unique with HOMO LUMO alignment such that there is a driving force for ground state charge transfer (rare) then CT states cannot be seen in absorption.
Dear Andy,
My question is usually at what range charge transfer band occurs? since i have seen CT band around 400nm in many articles on DSSCs and less than that is pi-pi*.
Are you sure they are CT? Do they show strong solvatochromism, if not they are not CT absorption bands.
Dear Sai,
when you write:
I wanted to know the range of pi-pi* and intramolecular charge transfer bands in the absorption spectrum of an organic dye (donor-spacer-acceptor).
It is too vague! Organic dye ! What a kind?
Please give more infos about your dye (DSSC) and spacer (-CH2- or rigid like R------R a.s.o...).
About DSSC : Please read this link :
http://www.diss.fu-berlin.de/diss/servlets/MCRFileNodeServlet/FUDISS_derivate_000000002568/02_2.pdf?hosts=
Note :
answerers cannot give good answers without joined infos (jpg or pdf...) in the question.
JRG
Theoretically, CT band, more precisely the Intramolecular Charge Transfer band in donor-pi-acceptor type of dyads should show solvatochromism, but in several cases, either the solvatochromism is very irregular (no regular trend by changing the solvent polarity) or is not at all present. In such cases, visualization of the FMOs (HOMO and LUMOs) can be helpful in making assignments.
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