A Molecular Architectural Approach to Second-Order Nonlinear Optical Materials
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Mat. Res. Soc. Symp. Proc. Vol. 392 @1995 Materials Research Society
characterization of NLO calix[4]stilbazole imine derivative with the calixarene frozen in a cone conformation. Furthermore, we discuss the construction of monolayers of the calixarene via covalent bonding to the silylated oxide surface, and second harmonic generation measurements on these self-assembled thin films. We find larger d33 values (60 pm/V) than those in ref. 4. RESULTS AND DISCUSSION 1. Design and Synthesis of Calixarene-Based NLO Chromophores Although many functionalized calixarenes have been synthesized, 5 preparation of calix[n]stilbazole (n = 4, 6, 8) and its derivatives has been proven to be more difficult. The major synthetic considerations are the solubility and the conformation freezing of the calixarenes. Our synthetic strategy is to first freeze the calixarene in a cone conformation by substituting the lower rim of the calix[4]arene and then to functionalize the upper rim of the calixarene for the incorporation of pyridyl units. The synthesis of imine derivative of calix[4]stilbazole is depicted 6 in scheme 1. Compound (1) and (2) were synthesized according to literature procedures. ,7 Reduction of nitrocalixarene (2) gave p-aminocalix[4]arene (3). The condensation of p-amino-
Scheme 1 Bt But
But
12
1 1) NO/H0H0 N
H2N 6
C1 H2
-Raney
6o
NO 2
02
02
0 2N
'Bu
2o NiI
0~
-0
0 chromphor (4.Altesrcue
er
y1
ofre
chromophore (4.Altesrcue eecnfimdb
28
M
n
IRat.
Irtn1
H2N2 NH2 H NM an Rdt.Apon
M
spectrum of (4) in CDCI 3 indicated that (4) has a rigid "cone" conformation with the D-it-A dipolar units aligned in the same direction; this was manifested by the fact that bridging methylene protons split into two doublets with strong coupling between them (J = 15 Hz). 5 The presence of long ethoxyethyl groups prevents flip-over of the individual rigid rod-like stilbazole units in (4) and the "cone" conformation is virtually frozen at room temperature. It is noteworthy, however, that the condensation reaction failed when the formyl and amino groups are switched. 2. Construction of Self-assembled Monolayer of (4) The construction of self-assembled monolayers of (4) is based on the approach reported by Li et al. 2a Silicon wafer and fused silica substrates were treated with a silane coupling agent pchloromethylphenyltrichlorosilane in either toluene or chloroform for 24 h, followed by a incubation of silylated substrate in 1 mM of compound (4) in toluene at 110 °C for three days. The monolayer was thoroughly cleaned by sonication in CHCI 3 , followed by vigorous rinsing with CHCI3 to remove any noncovalently bonded surface species.
0
f--1///I
//
O OHSiCI
0
3
___
00
N
N\
rjIK +HC1+jI
CH2CI
O
N
N
CHC
I
0
0 o os -)
Scheme 2
Ik
() (
CH2
UH2 OH2
HC
0_ _1_1_10
toluene, r.t.
/
toluene //'7-717 reflux
0'Si... _o,*SSiSi.,o, . o-Si lI/ii,
I
I//I/I/
I/t/f/I/I/lIz/f
The self-assembled monolayers consisting of pyramid-like imine derivative of calix[4]stilbazole were characterized by surface pol
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