Tuning the Förster Resonance Energy Transfer through a Self‐Assembly Approach for Efficient White‐Light Emission in an Aqueous Medium

Abstract

A simple and cost-effective methodology employing environmentally benign substances for the fabrication of white-light emitting materials is important for practical applications in the field of lighting and display devices. Designing purely organic-based white-light-emitting systems with high quantum efficiency in aqueous media is an unmet challenge. With this objective, a new class of pyridoindole-based hydrophobic fluorophore 6,7,8,9-tetrapropylpyrido[1,2-a]indole-10-carbaldehye (TPIC) was introduced. A strategy of self-assembly using nonionic surfactants was employed to enhance the fluorescence of TPIC in an aqueous medium and was exploited as energy donor. The steady-state and time-resolved emission spectra analysis revealed the micelle-mediated energy transfer from TPIC to Nile red (energy acceptor) leading to tunable fluorescence along with white-light emission. The white-light emitting aqueous solution was obtained with the Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of (0.33, 0.36) and significantly high quantum yield of 37 %. Solid-state white-light emission was achieved retaining the assembly of fluorophores in the form of a gel having the high quantum efficiency of 33 % with CIE coordinates of (0.32, 0.36); close to that of pure white light. The bright white luminescence of the inscription prepared using white-light emitting gel on a solid substrate offers promising applications for full-color flat panel displays.

Molecular Engineering Approaches Towards All‐Organic White Light Emitting Materials

“…White light emission by encapsulating the complementary emissive fluorescent molecules in nonemissive micelles was demonstrated by Patra and co‐workers . The incorporation of a new class of cyan‐emitting fluorophore, pyrido[1,2‐ a ]indole (TPIC) as a donor and red‐emitting Nile red (NR) as an acceptor in an aqueous micellar assembly (employing neutral surfactants, Triton‐X 45) led to tunable emission (Figure ).…”

“…Thus, white light emission in aqueous medium was achieved with CIE coordinates of (0.33, 0.36) and the quantum efficiency of 37 %. Interestingly, the strong white light emission was retained in the gel matrix (CIE: 0.32, 0.36, Φ f =33 %) when the WLE aqueous micellar solution of TPIC and NR was mixed with agarose gelator …”

“…Considering the concept of additive mixing, enormous attention has been paid by different research groups on the fabrication of WLE materials employing organic, inorganic, and organic–inorganic hybrid scaffolds . We restrict our discussion to the recent development of all‐organic WLE materials . The versatility and flexibility in terms of cost‐effective design and synthesis are the hallmark of molecular materials.…”

“…However, single excitation wavelength resulting emission from each of the dyes or chromophoric units is challenging . Tuning the fluorescence through encapsulation of single or multiple fluorophores in the supramolecular assembly of gels or micelles is one of the facile means to generate white light …”

Diversity-Oriented Synthesis and Optical Properties of Bichromophoric Pyrrole-Fluorophore Conjugates

“…At usual concentration two chromophores emit independently in solution (Sarkar et al, 2016 ). Likewise this effect can also be achieved by embedding in micelles, organic or hybrid matrices (For recent examples of photochromic and multichromophoric emitters embedded in micelles or matrices, see e. g., Findlay et al, 2014 ; Shi et al, 2015 ; Bälter et al, 2016 ; Joshi et al, 2016 ; Börgardts and Müller, 2017 ; Pallavi et al, 2018 ). Far more challenging, however, is the conceptual design of unimolecular bi- or multichromophores capable of polychromic emission (for reviews on organic white light emitting devices and materials, see Mukherjee and Thilagar, 2014 , 2015 ; Wu and Ma, 2016 ).…”