Fluorescence enhancement effect in pyrene and perylene doped nanoporous polystyrene films: Mechanistic and morphology

Abstract

Luminescent porous polystyrene (PS) films containing pyrene and various amounts of perylene were prepared in humid atmosphere by solution casting technique for use as a plastic scintillator. The fluorescence spectra of doped PS films monitored at pyrene excitation show quenching of monomer fluorescence of pyrene with simultaneous sensitization of perylene monomer fluorescence appearing towards red. The observed enhancement in fluorescence of perylene was explained by considering excitation energy transfer (EET) from pyrene to perylene molecules accommodated in the pores generated during film formation. The fluorescence quenching data do not fit into the Stern–Volmer relation, but the sensitized fluorescence is fitted by an exponential growth equation, y = 201 860 433.29 ex/0.64366 + 0.49262, with correlation coefficient R2 = 0.997. The results on absorption and excitation spectroscopy indicated that the pyrene and perylene filled in pores of the PS films exist as isolated molecules. The porosity of the films was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM), showing randomly oriented holes, and their mean size and size distribution were found to be depending upon the dopant concentration. Pyrene and perylene doped porous PS films prepared by solution casting method in humid atmosphere showed highly intense blue perylene fluorescence by fluorescence resonance energy transfer (FRET) at pyrene excitation. The SEM and AFM images revealed that nanosized pores are perylene concentration dependent, both pyrene and perylene held in the cavity of the pores in close proximal distance less than 10 nm is required to cause efficient energy transfer between them.

A polystyrene bearing perylene diimide pendants with enhanced solid state emission for white hybrid light-emitting diodes

“…PL spectrum of the blend consists of superposition of single PDI molecules emission, manifested by peaks at 534 nm and 577 20 nm, together with broad, featureless band at 627 nm, associated with aggregate fluorescence [33]. Emission of the most intense band of blend-16 corresponds very well with PL spectrum registered for PERY-VIN film, clearly demonstrating its aggregate origin.…”

“…After this time the mixture does not give any precipitate in methanol, indicating that only oligomers are formed. Then, we introduce the PERY-VIN co-monomer and proceed with the polymerization for an additional time (8 h for PS-PERY-8 and 16 20 h for PS-PERY-16). Following this synthetic pathway, we obtained two new copolymers comprising a PS backbone with pending PDI units, which differ by the molecular weight and PDI content, as reported in Table 1.…”

“…This hybrid system generates stable white light with CIE chromaticity coordinates (0.31, 0.34) and efficiency of 28 lm/W. 20 …”

“…While the tendency of PDI for crystallinity or close packing is widely exploited as n-channel materials for organic field effect transistors [14,15], 5 in order to extend the use of PDIs in other optoelectronic applications such as organic photovoltaics [16], LCD color filters [17], fluorescent sensors [18] and solar concentrators [19], researchers have explored different procedures for limiting or preventing PDI aggregation. These include dispersion in a transparent matrix [20], functionalization with bulky substituents [21][22][23][24], "grafting-to" immobilization [25] and copolymerization [26].…”

“…Chromaticity coordinates were only slightly dependent on voltage applied to the LED (∆x=0.03, ∆y=0.02). An advantage of our dye in20 comparison to many others is a filled gap between blue LED's peak and yellow emission, provided by TPD-FLU luminescence. This feature improves the color rendering index (CRI) parameter, which in case of our device is equal to 83, fulfilling the typical requirement for illumination application CRI > 80.…”