Colorimetric and Fluorescent ‘light-up’ Probe to Investigate ICT and a-PET Mechanisms for the Detection of Cu2+ and a Solid-State Emitter for the Visualization of Latent Fingerprints

Herein, we have reported the design and synthesis of Perylene tetra-(alkoxycarbonyl) (PTAC) derivative PTE-EA functionalized with tetraoctyl ester chains at the peri-positions and an electron donating/recognition group 2-aminoethanol (2-AE) at the mono bay-position. PTE-EA acted as colorimetric (visual color change of the solution from light-purple to yellowish-green) and fluorescence turn-on sensing probe for the molecular recognition of Cu2+ in binary aqueous-organic mixtures. The incremental addition of Cu2+ to the solution of PTE-EA in HEPES:CH3CN (3:7, v/v, pH 7.3) showed decrease in the ICT absorption band at 536 with new blue shifted absorption band (Δλ = 76 nm) at 460 nm. Further complexation with Cu2+ result in the significant enhancement of the fluorescence intensity at 520 nm (λex = 490 nm) via inhibition of the acceptor-excited photo-induced electron transfer (a-PET) process from 2-AE to the electron-deficient perylene tetraoctyl ester core. PTE-EA showed its applicability as a colorimetric/fluorometric probe for the detection of Cu2+ by adopting two conventional photophysical mechanism viz. ICT and a-PET and demonstrated high sensitivity with nano-molar detection limits (colorimetric = 18 nM and fluorometric = 16 nM) and the complex PTE-EAꓵCu2+ showed high association constant 4.3x106 M. Further, increase in the size after complexation revealed by the DLS data. Additionally, the other derivative of PTAC as bay-functionalized mono-brominated PTE-II with strong inherent solid-state fluorescence explored for the development of latent fingerprints (LFPs) on common household surfaces and visualized in the daylight by using naked eyes and under 365 nm UV lamp and we successfully achieved 2nd level of information from the data.