Prospects for Organic Dye Nanoparticles - Advanced Fluorescence Reporters in Chemistry and Biology - page 287

lower thermal stability and poorer mechanical properties compared to inorganic
materials, there were few routes for fabricating well-defined organic compounds
into nanostructures, resulting in difficulties in applying the top-down strategy that is
common in producing inorganic nanostructures. (2) Until recently, size-dependent
optical and electronic properties have not been anticipated in organic nanomaterials
because, unlike the case of Wannier excitons [ 12 ] in inorganic or semiconductor
crystals, the spectroscopic properties of organic crystals are essentially determined
by Frenkel excitons with a very smaller radius [ 13 ] or by monomer photochemistry.
However, in the 1990s, Nakanishi and co-workers succeeded in preparing some
kinds of organic dye nanoparticles systematically by adopting a “reprecipitation
method” as a facile synthetic technique [ 14 , 15 ]. After these epochal events, more
strategies have been developed for constructing organic nanostructures with inter-
esting morphologies and optical (absorption and fluorescence) properties. During
the course of many investigations, it was noticed that many photophysical proper-
ties exhibit an obvious size effect via aggregation of organic molecules. Emergence
of interesting fluorescent properties was also no exception. For example, perylene is
used in demonstrating the size dependent fluorescent properties [ 15 ]. Subsequently,
various types of organic dye compounds have been introduced to make fluorescent
organic nanoparticles. Figure 1 shows representative dye molecules that have been
used for producing organic nanoparticles with exciting fluorescence properties. As
a consequence of the variety and designability of organic dye molecules to convert

PDDP

N

N

N

DAP

N

N

Perylene

R

O

S

NH

PPB N O

HO HN

Tetracene

R = H : DHIA

R = t-

CN

Bu : DHBIA

HO

S

N

CN-MBE

H
N

C 12 H 25

N N

HN

O O

DASPE

N +

Si

ABAN

HPS

N

Fig. 1 Typical organic dye molecules that have been converted to fluorescent nanoparticles. The
abbreviation for each dye molecule is also shown in the figure