Highly Emissive Whole Rainbow Fluorophores Consisting of 1,4-Bis(2-phenylethynyl)benzene Core Skeleton: Design, Synthesis, and Light-Emitting Characteristics

Abstract

To create the whole-rainbow-fluorophores (WRF) having the small Δλem (the difference of λem between a given fluorophore and nearest neighboring fluorophore having the same core skeleton) values (<20 nm) in full visible region (λem: 400-650 nm), the high log ε (>4.5), and the high Φf (>0.6), we investigated molecular design, synthesis, and light-emitting characteristics of the π-conjugated molecules (D/A-BPBs) consisting of 1,4-bis(phenylethynyl)benzene (BPB) modified by donor groups (OMe, SMe, NMe2, and NPh2) and an acceptor group (CN). As a result, synthesized 20 D/A-BPBs (1a-5d) were found to be the desired WRF. To get the intense red fluorophore (Φf> 0.7, λem > 610 nm), we synthesized new compounds (5e-5i) and elucidated their photophysical properties in CHCl3 solution. As a result, 5h, in which a 4-cyanophenyl group is introduced to the para-position of two benzene rings in the terminal NPh2 group of 5d, was found to be the desired intense red fluorophore (log ε = 4.56, Φf = 0.76, λem = 611 nm). The intramolecular charge-transfer nature of the S1 state of WRF (1a-5d) was elucidated by the positive linear relationship between optical transition energy (νem) from the S1 state to the S0 state and HOMO(D)-LUMO(A) difference, and the molecular orbitals calculated with the DFT method. It is demonstrated that our concept (Φf = 1/(exp(-Aπ) + 1)) connected with the relationship between Φf and magnitude (Aπ) of π conjugation length in the S1 state can be applied to WRF (1a-5d). It is suggested that the prediction of Φf from a structural model can be achieved by the equation Φf = 1/(exp(-((ν̃a - ν̃f)(1/2) × a(3/2)) + 1), where ν̃a and ν̃f are the wavenumber (cm(-1)) of absorption and fluorescence peaks, respectively, and a is the calculated molecular radius. From the viewpoint of application of WRF to various functional materials, the light-emitting characteristics of 1a-5i in doped polymer films were examined. It was demonstrated that 1a-5i dispersed in two kinds of polymer film (PST and PMMA) emit light at the whole visible region and have the small Δλem values (<20 nm) and the high Φf values (>0.6). Therefore, the present D/A-BPBs can be said to be the desired WRF even in the doped polymer film.

Mixed Metal-Organic Dyes With Dual Electrophores: Designing More Robust Dyes for Light-Harvesting Applications

“…Calibrated to water13 C{ 1 H} NMR (100 MHz, acetone-d): δ = 148.51, 147.27, 133.20, 129.55, 125.19, 123.78, 122.20, 114.91, 84.07, 76.31. Spectroscopic data is consistent with the literature 75. …”

“…73 4.29c was synthesized by an Ullmann condensation, reacting aniline with iodo-anisole under reflux. 74 As shown in Scheme 4.3, iodinations were performed on each of the triphenylamine derivatives to install a good leaving group 73,75 , then a Sonogashira crosscoupling to TMS-acetylene, followed by a deprotection of the TMS group to yield a terminal alkyne (4.32a-c). 75 The procedures leading up to synthesizing 4.32a-c were followed from the literature with some minor modifications.…”

Virtual Design in Organic Electronics: Screening of a Large Set of 1,4-Bis(phenylethynyl)benzene Derivatives as Molecular Semiconductors

“…[4][5][6][7][8][9] In the last years, different electron-withdrawing and electron-donating aromatic rings have been incorporated within the generic BPEB structure to modify their light-emitting properties, and improve charge injection and transport efficiency concomitantly. [10][11][12][13][14][15][16][17][18][19][20] Moreover, the effect of the ethynylene group on electronic properties have also been studied extensively by means of Density Functional Theory (DFT) calculations. 7,8,21 The information derived from these calculations can be useful to guide the chemical synthesis of new BPEB derivatives.…”

Efficient Synthesis and Properties of [1]Benzothieno[3,2‐b]thieno[2,3‐d]furans and [1]Benzothieno[3,2‐b]thieno[2,3‐d]thiophenes

“…This should be due to intramolecular charge transfer from the BDTF unit to an electron-accepting unit. [8] In particular, 5b exhibited the strongest fluorescence among them (ΦPL = 0.85). More detailed optical data are summarized in Table S2.…”