The second-order nonlinear optical response of amine and
phenol/ether derivatives (1−8) has been
evaluated
using experimental and theoretical techniques.
Electric-field-induced second-harmonic generation (EFISH)
measurements establish that N-phenyl substitution of 4-nitroaniline
(1) produces a greater increase in molecular
hyperpolarizability than N-methyl substitution. In
contrast, O-phenyl substitution of 4-nitrophenol
(6) produces a
smaller increase in hyperpolarizability than O-methyl
substitution. Neither the enhancement of
hyperpolarizability
upon N-phenyl substitution nor the differential substituent
effect is anticipated on the basis of qualitative
arguments.
Careful theoretical analysis using semiempirical sum-over-states
and finite field calculations provide explanations
for both observed effects.
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