Second harmonic generation with 5-chloro-2-nitroaniline

DETAILED DESCRIPTION 5-Chloro-2-nitroaniline suitable for use in the present invention is crystalline in form, and is preferably in solid crystalline form.
Three crystal structures or polymorphs have been identified by X-ray powder diffraction.
One crystal structure of 5-chloro-2-nitroaniline that has been found to exhibit second harmonic generation shows it to belong to the noncentrosymmetric space group Pna2.
sub.
1, i.
e.
it crystallizes in a noncentrosymmetric configuration (see Stout, G.
H.
and Jensen, L.
H.
, "X-Ray Structure Determination," Macmillan Publishing Co.
, Inc.
: 1968, for a discussion on crystal structure analysis).
Non-centrosymmetric species are those which have no center of symmetry on either the molecular or crystalline unit cell level.
5-Chloro-2-nitroaniline is substantially transparent to electromagnetic radiation having wavelengths from 400-500 nm to 1000-1100 nm.
Accordingly, the compound is useful in second harmonic generators wherein both incident radiation and emergent radiation range from 500 nm to 1064 nm.
5-Chloro-2-nitroaniline is commercially available from Aldrich Chemical Co.
, Inc.
, Milwaukee, WI.
However, the commercial material is generally not the active form thereof, and it must be recrystallized from ethanol to obtain the form which exhibits second harmonic generation.
Alternatively, 5-chloro-2-nitroaniline can be synthesized by the acylation and nitration of 3-chloroaniline, followed by hydrolysis and separation of the resultant chloronitroaniline isomers, 5-chloro-2-nitroaniline and 3-chloro-4-nitroaniline following an acylation, nitration, and hydrolysis scheme similar to that described in Howard, J.
C.
, Org.
Syn.
, IV 1963, 42-45.
Devices that are capable of generating coherent second harmonic light radiation with 5-chloro-2-nitroaniline described herein are well known in the art.
Representative examples of such devices are described in U.
S.
Pat.
Nos.
3,395,329; 3,431,484; and 3,858,124; and U.
S.
patent application Ser.
Nos.
925,300 (now U.
S.
Pat