# The Polymorphism of Orlyum White 520T, an Ultraviolet Luminescent Security Ink

## TL;DR

The study discovers two new stable forms of a security ink compound with higher melting points and different crystal structures.

## Contribution

The discovery of two new polymorphic forms of Orlyum White 520T with higher stability and distinct crystal structures.

## Key findings

- Two new polymorphic forms (Form I and Form II) with melting points of 197–198 °C and 195–196 °C were identified.
- The new forms differ in powder XRD patterns and FT-IR spectra despite identical elemental and NMR data.
- Solvents and organic contaminants likely influence the formation of different polymorphs.

## Abstract

The polymorphism of the ultraviolet luminescent security ink Orlyum White 520T (N-(2-(4-oxo-4H-benzo[d][3,1]-oxazin-2-yl)phenyl)naphthalene-2-sulfonamide) is revealed, obtaining two new polymorphic forms with enhanced stability. Beyond the known form (lit. mp. 184.8–185.2 °C, Form III, YOCTAO), we succeeded in gaining two new polymorphic forms, Form II and Form I, with higher melting points of 195–196 and 197–198 °C, respectively. Their elemental composition, 1H and 13C NMR spectra have been found to be identical, while their powder XRD patterns and FT-IR spectra are significantly different. Based on the single-crystal structure determination of Form II and redetermination of Form III, we uncover the similarities and differences in their packing arrangement and in their secondary interaction systems, all of which affect the molecular conformations in their crystals. In order to explain their significantly distinguishable melting points, Hirshfeld surface analysis and lattice energy calculations have also been carried out. We have made efforts toward revealing the reproducible conditions under which certain polymorphs are formed. It seems that the solvents or other probable organic contaminations are more likely responsible for the formation, nucleation and growth of crystals of various polymorphic forms, traced by thermogravimetric evolved gas analysis (TG/DTA-EGA-MS).