Diarylamino- and Diarylboryl-Substituted Donor–Acceptor Pyrene Derivatives: Influence of Substitution Pattern on Their Photophysical Properties

Abstract

Dianisylamino donor (D) and dimesitylboryl acceptor (A) substituents were introduced at the 1,6- and 2,7-positions of pyrene to demonstrate that the substitution patterns influence the photophysical properties. The different pictures in orbital interactions between the pyrene core and the D-A substituents led to the outcome that 1,6-substituted pyrene derivative 1 had stronger electron-donating and electron-accepting properties in conjunction with a small HOMO-LUMO gap, as compared to the 2,7-substituted derivative. For these pyrene derivatives, modest (Φ = 0.2) to strong (Φ = 1.0) fluorescence was detected in degassed organic solvents; 1 exhibited a typical intramolecular charge transfer (ICT) emission obeying energy-gap law, while 2 displayed a moderate inverse energy-gap law, originating from the different substitution patterns. Although theoretical calculations predicted that both 1 and 2 adopt highly twisted ICT excited states (TICT excited states) even in the gas phase, but practically, it was suggested that the observed photophysical properties could be determined by the extent of twist angle of the TICT-like excited state in accordance with the solvent polarity. Moreover, the bulky D-A substituents inhibit the intermolecular direct π-π interactions, thereby resulting in the bright and moderate solid-state emissions for 1 (Φ = 0.76) and 2 (Φ = 0.21), respectively.

Pyrene Molecular Orbital Shuffle—Controlling Excited State and Redox Properties by Changing the Nature of the Frontier Orbitals

“…We note that Ito et al. have reported apparent Stokes shifts of the D‐π‐A compound H ranging from 3292 cm −1 in hexane ( λ max (em)=458 nm) to 8649 cm −1 in acetone ( λ max (em)=600 nm) . However, these very high values are the result of an incorrect excited state assignment.…”

“…Slightly and significantly shorter N−C bonds are observed in 11 (1.391(3) Å) and 6 (1.379(2) Å), respectively (Table ). In contrast, the N−C(pyrene) bond length of 1‐(dimesitylboryl)‐6‐(di‐4‐anisylamino)pyrene, a positional isomer of H (Scheme ) (1.442(4) Å), in which the functional groups are located at the 1,6‐positions, is significantly longer . The sum of the C‐N‐C angles involving the julolidine moiety is similar in compounds 4 , 8 , and 9 (350(1)° on average), slightly larger in 11 (355.7(6)°), and varying between about 344° and 350° in 14 (Table ).…”

“…During the preparation of our manuscript, Ito and co‐workers reported the occurrence of a TICT state in the D‐π‐A compound H , bearing dianisylamino donors, leading to strong solvatochromism . However, the reported apparent Stokes shifts and excited state assignments in the absorption spectra are incorrect, as we will demonstrate in our discussion below.…”

Synthesis, Photophysical and Electronic Properties of New Red‐to‐NIR Emitting Donor–Acceptor Pyrene Derivatives

“…[28] Moreover, previous studies demonstrated that strong p-donors/acceptors are able to switch the energetic ordering of its HOMO/HOMOÀ1 and LUMO/LUMO + 1, respec-tively, which results in greatly influenced photophysical and redox properties of these derivatives. [15,[29][30][31][32] Unsymmetrical substitution at these positions is straightforward via iridiumcatalyzed CÀH borylation, [33][34][35] and the introduction of julolidine-like donors at the 2,7-positions (I, Scheme 2) even resulted in an unusual green luminescence. [15,[29][30][31][32]36] The K-region (positions 4,5,9,10, Figure 1) has large HOMO/ LUMO as well as HOMOÀ1/LUMO + 1 contributions.…”

“…[15,[29][30][31][32] Unsymmetrical substitution at these positions is straightforward via iridiumcatalyzed CÀH borylation, [33][34][35] and the introduction of julolidine-like donors at the 2,7-positions (I, Scheme 2) even resulted in an unusual green luminescence. [15,[29][30][31][32]36] The K-region (positions 4,5,9,10, Figure 1) has large HOMO/ LUMO as well as HOMOÀ1/LUMO + 1 contributions. Ottonelli and co-workers showed [37] that the contribution to the HOMO/ LUMO increases in the order: 2,7 < 4,5,9,10 < 1,3,6,8, while contributions to the HOMOÀ1/LUMO + 1 increase in the order 4,5,9,10 < 1,3,6,8 < 2,7.…”