Picosecond spectroscopy and hyperlinear photoluminescence in poly(para-phenylene)-type ladder polymers

Abstract

In our investigations of the photoluminescence in poly-͑para-phenylene͒-type ladder-polymer films a highly nonlinear dependence of the emission spectra is observable at elevated excitation densities. A spectral redistribution results in the hyperlinear increase of emission efficiency in the blue region, as the vibronic 0-1 transition (ϭ492 nm) becomes the most predominant radiative relaxation. The detailed study of temporal decay and spectral evolution of luminescence provided by streak camera measurements performed in the temperature range Tϭ20-300 K reveals the spectrum being composed by the contributions of two different emitting species, namely, S 1 -singlet states and aggregates. The material is found to be photochemically stable and luminescence does not seem to be limited by saturation effects even under high-excitation conditions, which is essential for laser application. ͓S0163-1829͑97͒03427-9͔ PICOSECOND SPECTROSCOPY AND HYPERLINEAR . . .

Exciton diffusion and relaxation in methyl-substituted polyparaphenylene polymer films

“…Third, the annihilation rate is time independent within experimental accuracy, at least on tens of picosecond time scale, and equals to about 1.3ϫ 10 −8 s −1 cm 3 . Values of the linear relaxation times are within the range of literature data for m-LPPP films, which are widely distributed between 8 and 300 ps 28,[33][34][35][36][37]. …”

Interaction of singlet excitons with polarons in wide band-gap organic semiconductors: A quantitative study

“…However, lowering the temperature to 20 K increases PL to 50% due to a lower nonradiative decay rate. 47 Since the intrinsic lifetime and, hence, k r are determined by the quantummechanical transition matrix element, which is per se temperature independent, k nr ϭ10 9 s…”

Time-resolved study of luminescence in highly luminescent disubstituted polyacetylene and its blend with poorly luminescent monosubstituted polyacetylene

“…The redshift of PL spectra with time has also been observed in other polymers such as PPV and its derivatives, 27 as well as in ladder-type poly͑para-phenylene͒ ͑LPPP͒. 28 In the case of PPV and its derivatives, the redshift has been explained by the exciton migration from short conjugation segment to the longer one, resulting in a fast non-single-exponential PL decay at short wavelengths, but a slow single-exponential decay at longer wavelengths because the excitons in a long conjugation segments cannot be transferred further. On the other hand, in LPPP, the redshift was explained by the transfer of excitation energy between two different emitting species, that is, from singlet exciton states to aggregate states.…”