A detailed investigation of light-harvesting efficiency of blue color emitting divergent iridium dendrimers with peripheral phenylcarbazole units

Abstract

The increase in phosphorescence efficiency was estimated by the energy transfer mechanism for divergent iridium dendrimers with peripheral phenylcarbazole units. A series of Ir-core/phenylcarbazole-end dendrons of the type, Ir(dfppy)2(pic-Czn) (Gn, n = 0, 1, 2, and 3), was synthesized, where dfppy, pic, and Czn (n = 2, 4, and 8) are 2-(4,6-difluorophenyl)pyridine, picolinate substituted with Czn at the 3-position, and 4-(9-carbazolyl)phenyldendrons connected with 3,5-di(methyleneoxy)benzyloxy branches, respectively. Selective excitation of the Czn units of G1–G3 resulted in >90% quenching of the Cz fluorescence accompanied by the growth of phosphorescence from the Ir(dfppy)2(pic) core as a consequence of energy transfer from the excited-singlet Czn chromophore to the core. The rate constants of energy transfer were determined by steady-state and transient spectroscopic measurements to be 4.32 × 10(9) s(−1) (G1), 2.37 × 10(9) s(−1) (G2), and 1.46 × 10(9) s(−1) (G3), which were in good agreement with those calculated using the Förster model. The phosphorescence enhancements were 157 (G1), 213 (G2), and 264% (G3) when compared to the phosphorescence of the core Ir(dfppy)2(pic-Ph2) (G0), in which pic-Ph2 is 3-(3,5-dibenzyloxybenzyl)picolinate.

De novodesign of D–σ–A molecules as universal hosts for monochrome and white phosphorescent organic light-emitting diodes

“…Compared with BII–TPA, BII–BCz emits shorter-wavelength fluorescence with dual peaks both in solutions and films. The fluorescence profiles of BII–TPA and BII–BCz are similar to those of their donor moieties with no evidence of ICT properties 33,34. We also measured the fluorescence spectra of BII–BCz and BII–TPA in solutions with different polarities (Fig.…”

“…Both BII derivatives show the n–π* electronic transition of BI peaking around 300 nm 31. The characteristic absorption bands of carbazole derivatives are observed in BII–BCz at 286 nm ( 1 L a ← 1 A transition, strong) and ∼330 nm ( 1 L b ← 1 A transition, weak),32,33 while the strong absorption band at 247 nm can be ascribed to the π–π* transition. A small peak at 261 nm in the BII–TPA absorption profile, which is not found in BII–BCz, can be attributed to the n–π* transition of the TPA moiety.…”

BODIPY functionalized o-carborane dyads for low-energy photosensitization

“…The nanosecond transient absorption measurements were conducted using laser flash photolysis. 29 The samples were excited by third-harmonic generation (355 nm, FWHM of 4.5 ns) from a Q-switched Nd:YAG laser (Continuum, Surelite II-10). Light from a xenon arc lamp (ILC Technology, PS 300-1) was focused on the sample for the transient absorption measurements.…”

Improving the Electropolymerization Properties of Fluorene-Bridged Dicarbazole Monomers through Polyfluoroalkyl Side Chains

“…CFC monomers exhibit two clear absorptions bands at ∼290 and ∼340 nm. The light absorption at 290 nm is due to the π–π* electron transition of the carbazole moiety, whereas the lower-energy transition is assigned to electron transfer from nitrogen lone pairs to the π* orbital of fluorene. ,,,− As reported in Table , the π–π* electron transition occurs at the same wavelength for both dyes, as the torsion that allows the σ-bonding between the carbazole and fluorene moieties minimizes the extension of the conjugation length between the two aromatic centers. On the other hand, the band assigned to the electron transfer processes between carbazole and fluorene is 4 nm shifted toward lower energy for CFC-F1 with respect to CFC-H1 , which indicates the existence of a residual inductive effect exerted by the polyfluorinated alkyl chains.…”