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Fluorescence and photoisomerization studies of p-nitrophenyl-substituted ethenylindoles

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Title Fluorescence and photoisomerization studies of p-nitrophenyl-substituted ethenylindoles
 
Creator SINGH, AK
HOTA, PK
 
Subject intramolecular charge-transfer
dual fluorescence
stilbenes
relaxation
state
alpha,omega-diphenylpolyenes
aminobenzonitriles
derivatives
rhodopsin
pathways
indole
ethene
fluorescence
photoisomerization
charge transfer
 
Description The synthesis, electronic absorption, fluorescence (lambda(f), lambda(ex), Phi(f), tau(f)) and photoisomerization (Phi(t -> c), photostationary state composition) properties of 3-(4-nitrophenylethenyl-E)-NH-indole (1), 3-(4-nitrophenylethenylE)-N-ethylindole (2) and 3-(4-nitrophenyl ethenyl-E)-N-benzenesulfonylindole (3) in organic solvents of varying polarity are reported. The absorption maximum of these compounds undergoes a moderate red shift with increasing solvent polarity. However, the fluorescence maximum becomes highly red shifted with increasing solvent polarity. Whereas I and 2 show broad fluorescence bands, 3 exhibits dual fluorescence. Further, I and 2 fluoresce much more efficiently than 3. Correlation of the Stokes shift with solvent polarity parameters such as Delta(f) and E-T(30) and excited-state dipole moment indicate a highly polar excited state for 1-3. Time-resolved fluorescence studies show that the fluorescence decays are single-and multi-exponential type, depending on the solvent polarity. Further, I and 2 do not show photoisomerization on irradiation. However, 3 is photoactive and shows efficient photoisomerization in non-polar heptane. The sensitivity (p) of the photoreaction is determined in various solvent in terms of the Hammett plot, which showed that the excited states involved are electron deficient in nature and consequently stabilized more by an electron sufficient polar solvent and electron donating substituent. These results led us to suggest the existence of three types of excited states, namely the locally excited state, the intramolecular charge-transfer excited state and the conformationally relaxed intraniolecular charge-transfer excited state in the photoprocesses of these compounds. Copyright (c) 2005 , Ltd.
 
Publisher JOHN WILEY & SONS LTD
 
Date 2011-08-16T21:50:52Z
2011-12-26T12:55:09Z
2011-12-27T05:43:49Z
2011-08-16T21:50:52Z
2011-12-26T12:55:09Z
2011-12-27T05:43:49Z
2006
 
Type Article
 
Identifier JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 19(1), 43-52
0894-3230
http://dx.doi.org/10.1002/poc.987
http://dspace.library.iitb.ac.in/xmlui/handle/10054/9633
http://hdl.handle.net/10054/9633
 
Language en