Data di Pubblicazione:
2010
Citazione:
The role of ion pairs in the second-order NLO response of 4-X-1-methylpiridinium salts / F. Tessore, E. Cariati, F. Cariati, D.M. Roberto, R. Ugo, P.R. Mussini, C. Zuccaccia, A. Macchioni. - In: CHEMPHYSCHEM. - ISSN 1439-4235. - 11:2(2010 Feb 01), pp. 495-507.
Abstract:
A series of 4-X-1-methylpyridinium cationic nonlinear optical
(NLO) chromophores (X=(E)-CH=CHC6H5; (E)-CH=CHC6H4-4’-
C(CH3)3; (E)-CH=CHC6H4-4’-N(CH3)2; (E)-CH=CHC6H4-4’-N(C4H9)2 ;
(E,E)-(CH=CH)2C6H4-4’-N(CH3)2) with various organic (CF3SO3
, p-
CH3C6H4SO3
), inorganic (I , ClO4
, SCN , [Hg2I6]2 ) and organometallic
(cis-[Ir(CO)2I2] ) counter anions are studied with the
aim of investigating the role of ion pairing and of ionic dissociation
or aggregation of ion pairs in controlling their secondorder
NLO response in anhydrous chloroform solution. The
combined use of electronic absorption spectra, conductimetric
measurements and pulsed field gradient spin echo (PGSE)
NMR experiments show that the second-order NLO response,
investigated by the electric-field-induced second harmonic
generation (EFISH) technique, of the salts of the cationic NLO
chromophores strongly depends upon the nature of the counter
anion and concentration. The ion pairs are the major species
at concentration around 10 3m, and their dipole moments
were determined. Generally, below 5 10 4m, ion pairs start to
dissociate into ions with parallel increase of the second-order
NLO response, due to the increased concentration of purely
cationic NLO chromophores with improved NLO response. At
concentration higher than 10 3m, some multipolar aggregates,
probably of H type, are formed, with parallel slight decrease of
the second-order NLO response. Ion pairing is dependent
upon the nature of the counter anion and on the electronic
structure of the cationic NLO chromophore. It is very strong
for the thiocyanate anion in particular and, albeit to a lesser
extent, for the sulfonated anions. The latter show increased
tendency to self-aggregate.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Aggregation; Cations; Chromophores; Ion pairs; Nonlinear optics
Elenco autori:
F. Tessore, E. Cariati, F. Cariati, D.M. Roberto, R. Ugo, P.R. Mussini, C. Zuccaccia, A. Macchioni
Link alla scheda completa: