As far as organic nanoparticles are concerned, they shows red shift in wavelength for fluorescence spectroscopy studies with respect to their parent molecule. Is their any possibility for occurrence of blue shift in wavelength for organic nano particles studied by florescence spectroscopy.
Yes, blue shifted emission can be observed in nano particles. When you talk about nano particles, then you are talking about molecules in aggregate form. Now in aggregate state, intermolecular interactions dominates over solute solvent interactions. Generally, the red shift observed in nano particles is due to inter molecular charge transfer state (ICT), or due to planarisation of molecule in aggregates leading to extension of conjugation.
however, in some cases when a molecule is sterically congested ( like dendrimer) and can not pack closely in aggregate form, you may observe blue shifted emission as the intermolecular interactions are well averted due to the bulky structure of the molecule. or you can also say that if the intermolecular interactions are weaker than solute-solvent interactions, then blue shifted emission can be observed.
Yes; it can .
Before starting, let us first know very briefly the anologies between UV and fluorescence spectroscopies(FS).
It can be said just as in conjugated systems, we have π, π* and inbetween lies the n( nobonding orbitals) in UV, similarly we have Jablonski diagram in FS with analogous equivalences: So, S1 and T( ground singlet, excited singlet and triplet state) respectively.
The organo NP with nonbonding electrons are able to interact with the hydrogen bonding solvents to a greater extent in the ground state than in their excited state. As a result, n- π*[T- S1]transition will shift towards the shorter wave length as the hydrogen bonding ability of the solvent increase. A shift towards the shorter wave length is called hypsochromic effect( blue shift) A simplest form of equivalence in UV and Jablonski diagram of FS is given in the attachment along with.
Yes, blue shifted emission can be observed in nano particles. When you talk about nano particles, then you are talking about molecules in aggregate form. Now in aggregate state, intermolecular interactions dominates over solute solvent interactions. Generally, the red shift observed in nano particles is due to inter molecular charge transfer state (ICT), or due to planarisation of molecule in aggregates leading to extension of conjugation.
however, in some cases when a molecule is sterically congested ( like dendrimer) and can not pack closely in aggregate form, you may observe blue shifted emission as the intermolecular interactions are well averted due to the bulky structure of the molecule. or you can also say that if the intermolecular interactions are weaker than solute-solvent interactions, then blue shifted emission can be observed.
Thank you Gopal and Manohar sir..............
Yet......... I am confused that if Nano particles are aggregation of molecules then there is possibility of red shift in wavelength for fluorescence but if we observe blue shift then is it because of some electron withdrawing groups in monomer molecule or lone pair containing groups such as ketone.
Dear Prasad
Nano particle or aggregation does not always means red shift of fluorescenec. It depends upon the packing behavior or intermolecular interactions in aggregates. it depends upon how the different groups in the molecule are interacting with each other and with the groups of other molecules in its vicinity in aggregated state. I am attaching two papers which have blue shifted emission in aggregation and will help you better understand the phenomena. Everything is available in literature, you just need to put some more efforts to find them.
All the best
A specific case of aggregation which leads to absorption blue shift is the so-called H-dimer (face to face )
Rene sir........ Yes i agree with you that about absorption spectroscopy studies. I would like know about the fluorescence spectroscopy studies changes in wavelength after preparation of nano particles w.r. to their parent one. (Specially blue shift)
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