Charge Recombination Luminescenceviathe Photoionization of a Dopant Chromophore in Polymer Solids

Abstract

The behavior of a photoejected electron with the parent cation formed through two-photon ionization of a dopant chromophore in poly(alkyl methacrylate)s and polystyrene was studied by measurement of the emission spectra of the charge recombination luminescence, i.e., isothermal luminescence (ITL) at 20 K and thermoluminescence (TL) at temperatures from 20 to 300 K. The ITL spectral shape remained the same between 10 min and 10 h after the photoirradiation. On the other hand, the intensity ratio of phosphorescence (I P) to fluorescence (I F), I P/I F in the TL spectra increased for poly(alkyl methacrylate)s above a temperature where small scale motions of the main chain are released but was almost constant for polystyrene in the temperature range examined. These findings show that, for poly(alkyl methacrylate)s, the photoejected electrons change into more stable anion species with a motional relaxation of the polymer. From the TL spectral change, the depth of the deeper trap at higher temperatures was estimated to be more than 1.8 eV.

Time-gated triplet-state optical spectroscopy to decipher organic luminophores embedded in rigid matrices

“…Such properties are intrinsic to charge transfer (CT) or excitonic transitions. [13][14][15][16]20 This suggests that the 255 nm (S 2 ) excitation of the a centers is of delocalized CT nature. Similarly, the 295 nm, 325 nm, 345 nm, etc.…”

Influence of energy gap between charge-transfer and locally excited states on organic long persistence luminescence

“…1 H nuclear magneticresonance (NMR) ( Supplementary Fig. 19) and 13 C NMR spectra ( Supplementary Fig. 20) were recorded with a Bruker AVANCE III 500 MHz spectrometer.…”

“…The LPL process is governed by the recombination of dissociated radical cations and anions with a power-law emission decay 5,9,10 , so that the emission duration of OLPL materials is significantly longer than that of conventional room-temperature phosphorescence, which is ideally a first-order reaction with an exponential emission decay 1,2,11,12 . The power-law kinetic results (power-law kinetic, I(t)~t −m , m = 0.1-2) from charge recombination can be explained by several physical models discussed in previous literatures about LPL from organic molecules (N,N,N′,N′-tetramethylbenzidine (TMB)/poly(alkyl methacrylate)s) 13 and thermoluminescence of the inorganic LiF 14 , and the organic molecule polyethylene terephthalate 15 . These models can be separated into the diffusion model 9,10,16,17 and the electron tunneling model 18 of geminate ion recombination.…”

Self‐Stabilized Amorphous Organic Materials with Room‐Temperature Phosphorescence

“…In 2017, the Adachi group reported an ultra‐long persistent luminescent material based on an organic photo‐induced charge separation system . Through low energy density laser excitation, the neutral host–guest molecule pair of the strong electron‐accepting molecule 2,8‐bis(diphenylphosphoryl)dibenzo[b,d] thiophene (PPT) and strong electron‐donating molecule N , N , N , N ‐tetramethylbenzidine (TMB) can be effectively converted into radical ion pairs, lengthening the phosphorescence lifetime to the minute level . However, although the structure was in an amorphous state, the luminescent components still need the protection of tight polymer encapsulation against air.…”