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Unveiling the Hidden, Dark, and Short Life of a Vibronic State in a Boron Difluoride Formazanate Dye
Author(s) -
Melenbacher Adyn,
Dhindsa Jasveer S.,
Gilroy Joe B.,
Stillman Martin J.
Publication year - 2019
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201908999
Subject(s) - excited state , luminescence , excitation , chemistry , wavelength , boron , vibronic spectroscopy , stokes shift , ground state , atomic physics , photochemistry , vibronic coupling , chromophore , molecular physics , materials science , physics , optoelectronics , organic chemistry , quantum mechanics
Boron difluoride (BF 2 ) formazanate dyes are contenders for molecular species that exhibit a large Stokes shift and bright red emission. Excitation of 3‐cyanoformazanate complexes with 10 μs wide pulses of specific wavelengths resulted in strong luminescence at 663 nm at both room temperature in solution and at 77 K in a frozen solution. Analysis of the short‐lived excitation spectrum from this luminescence shows that it arises from a vibronic manifold of a higher‐lying excited state. This dark state relaxes to the emitting state over 10 μs. TD‐DFT calculations of the two lowest‐energy excited states show that the relaxed geometries are planar for S 1 but highly distorted in S 2 . The specific time‐ and wavelength‐dependence of the excitation profile provides a unique optical encryption capability through the comparison of emission intensities between adjacent vibronic bands only accessible in the 0–12 μs time domain.