External heavy-atom effect in room-temperature phosphorescence

Abstract

The effect of external heavy-atom perturbers on the roomtemperature phosphorescence (RTP) spectrum of dibenzo-[f,h]quinoxaline (DBO) adsorbed on Whatman 4 fllter paper is reported. The totally symmetric vibrational bands are predominantly enhanced, leading to a spectral change in vibratbnal structure. Inhomogeneity effects of moiecule-perturber interactions are investlgated by time-resolved phosphorimetry and lifetime measurements.Room-temperature phosphorescence (RTP) is a sensitive and simple analytical method to characterize molecules adsorbed on solid substrates (I). Originally observed from compounds adsorbed onto solids (2,3), the RTP phenomenon has been further developed for chemical analysis of organic species in solid substrates (4-7) as well as liquid media (8,9). In particular, it has been successfully applied to the detection of polyaromatic hydrocarbons (PAHs) and N-heterocycles in environmental samples (10-13). Filter paper is the most widely used substrate for RTP, since it is inexpensive and commercially available. The corresponding sample preparation is also simple and rapid: only 2-5 yl of the sample solution is required for a typical assay. The solution is spotted on the paper, and after thorough drying in a stream of hot air or under an IR lamp, the sample is ready for measurement in a spectrometer equipped with a standard phosphoroscope ( I ) .In previous works, we have investigated photophysical aspects related to the interactions of molecules with the substrate: the guest-host interaction (electron-phonon coupling) on a filter paper substrate was studied by measuring laserinduced phosphorescence line narrowing (14). Hydrogenbonding interactions were investigated by using two-dimensional total luminescence spectroscopy (15). In this work we investigate the external heavy-atom effect in R T P and study experimental factors that could affect analytical applications.The sensitivity of R T P may be drastically increased by the external heavy-atom effect (16)(17)(18)(19) and limits of detection in the picogram range have been achieved. The filter paper may be impregnated with a heavy-atom solution prior to spotting the analyte solution or the two solutions may be spotted simultaneously. The heavy-atom enhancement factors depend not only on the concentration but also on the particular properties of the heavy atoms used: high enhancement factors have been found with T1+ and Pb2+ for PAHs and with I-and Hg2+ for N-heterocycles (13). Apart from the overal phosphorescence intensity enhancement, other effects such as spectral shifts and changes in the spectral intensity profiles, due to external heavy-atom perturbers, should also be considered in the interpretation of R T P spectra. Short and long RTP decaying components of several indoles on ion-exchange paper substrates have been previously reported (20). In a recent work (13) it was demonstrated, that R T P spectra of N-heterocycles are red-shifted-compared to the spectrum obtained with no heavy-atom perturbers-when using HgCl, as the heavy atom sal...

Two Are Better Than One: A Design Principle for Ultralong‐Persistent Luminescence of Pure Organics

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Twenty-fold Enhancement of Gadolinium-Porphyrin Phosphorescence at Room Temperature by Free Gadolinium Ion in Liquid Phase

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