Unique molecular aggregation of novel naphthalocyanine (near IR absorbing dye)

Abstract

A series of organic-soluble naphthalocyanine derivatives (Y m MNcX 4) have been synthesized. Their spectroscopic properties in organic solutions and in thin films were studied. MNcX 4 such as MNc(t-Bu) 4 ( 5a-5c) and MNc(On-Bu) 4 ( 5j) formed H-aggregates even in dilute solutions. MNc(CO 2R') 4 ( 5d-5i) had much stronger H-aggregation properties compared with those ofMNc(t-Bu) 4 and MNc(On-Bu) 4. Especially, MNc(CO 2R') 7 complexes (M=Cu, Pd and Ni) existed exclusively without monomers in the aggregated state even in highly dilute solutions. MNcX 4, which has strong H-aggregation properties, showed merely H- aggregate absorption maxima in thin films. In contrast, Y 2MNcX 4 ( 4), which has sterically hindered Y groups, showed monomerically pure characteristics in solution. However, thin films of Y 2MNcX 4 have a J-type molecular arrangement, exhibiting a red shift of Q-band absorption. The monomeric properties of Y 2MNcX 4 in solutions and J-type molecular arrangement in thin films arise from steric hindrance of two Y groups, such as R 3SiO-in Y 2MNcX 4, which prevents strong H-aggregation of naphthalocyanine.