Ak. Dutta et al., AGGREGATION-INDUCED REABSORPTION OF P-TERPHENYL IN LANGMUIR-BLODGETT-FILMS - A SPECTRAL STUDY, Journal of physical chemistry, 98(49), 1994, pp. 12844-12848
Mono- and multilayers of nonamphiphilic p-terphenyl (TP) mixed with a
fatty acid have been incorporated in Langmuir-Blodgett (LB) films. The
surface pressure-area isotherm suggests that the molecules stand almo
st vertically at the air-water interface. In LB films and in ethanol-w
ater binary mixtures, both (1)L(a) and (1)L(b) bands appear in absorpt
ion spectra, the latter being absent in pure ethanol. The appearance o
f the (1)L(b) band has been attributed to the organization of TP molec
ules. The higher energy bands of the emission spectra in solution are
not manifested in the LB film. This phenomenon has been attributed to
reabsorption induced by aggregation. This has been further verified by
the emission spectra in ethanol-water mixtures. The role of the (1)L(
b) band as the reabsorbing state in LB films has been supported by exc
itation spectra. Comparison of the emission and excitation spectra of
TP in solution, in LB films, and in ethanol-water mixtures suggests fo
rmation of low-dimensional aggregates of TP molecules in LB films. Sca
nning electron microscopy also supports the existence of such aggregat
es in LB films.