True-Photonic Strategy for Chemically Encrypted Two-Factor Authentication with Unlimited Chemical Passwords Based on Cascade Energy Transfer under a Single Wavelength Excitation

Here, we report a simple generalized platform for a molecular password system based on zero- to three-step excitation energy transfer involving four readily available commercial fluorescent dyes, Coumarin 1, Curcumin, Rhodamine 123, and Rhodamine B, under single wavelength excitation at 360 nm in 9:1 (v/v) 1,4-dioxane–acetonitrile. The input keys or password characters are chemically composed and defined by the quaternary concentrations of four individual dyes, and the fluorescent readouts at multiple wavelengths against such unique dye compositions identify each character. These passwords could be encrypted and communicated as sets of quaternary concentration values or sets of points on a principle component analysis (PCA) graph that would be difficult to understand without the identities of the dyes, involved chemical process, and solvent composition. The primary drawback of the reported chemical password systems is the limited number of active passwords that prevents them from real applications. The present molecular password system supports all-active 44 (256) four-character passwords from four chemical inputs and the password length could be increased to generate 45 (1024) five-character, 46 (4096) six-character, 47 (16 384) seven-character, and 48 (65536) eight-character passwords, which have been partially demonstrated. The system retains the scope to increase the password length further. Such a dynamic nature of chemical passwords makes the molecular security system perfect for complex applications like two-factor authentication (2FA) that demands the simultaneous verification of long static passwords as well as short one-time passwords. Chemical passwords, spectroscopic verification, and strong chemical encryption eventually must make the 2FA process most secured. We present here the rationale to design a robust molecular password system as a powerful tool for data processing and information protection through chemical encryption that would work well with another set of molecules too.