Akihiro Ito

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

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 (ΦF = 0.2) to strong (ΦF = 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 (ΦF = 0.76) and 2 (ΦF = 0.21), respectively.

Macrocyclic oligoarylamines as hole- and spin-containing scaffolds for molecule-based electronics

Calixarenes have been widely utilized in all facets of supramolecular chemistry over the past four decades. As a new variety in the calixarene family, the nitrogen-bridged calixaromatics, namely aza[1n]cyclophanes, have been emerging as macrocyclic host molecules. However, that is not the whole picture at all: a wealth of two- and/or three-dimensionally networked molecular structures due to ortho-, meta-, and para-phenylene-bridging modes creates diverse charge distributions as well as multi-spin alignments depending on their oxidation states. This review article will provide a summary of research into the macrocyclic oligoarylamines with a variety of arene-bridged patterns and their various features as hole- and spin-containing scaffolds.

Luminescent Superbenzene with Diarylamino and Diarylboryl Groups

Dianisylamino donor and dimesitylboryl acceptor substituents were introduced at the 2,11-positions of hexa-peri-hexabonzocoronene (HBC) to demonstrate an effective fluorescent enhancement of HBC as virtually nonfluorescent superbenzene. The present donor-acceptor substitution replaced the typical weak α-band with an intense intramolecular charge-transfer band in the absorption spectrum, thereby leading to a much larger fluorescence quantum yield (Φf = 0.56 in CH2Cl2) than any other HBC derivatives.

Tetraaza[1.1.1.1]m,p,m,p-cyclophane Diradical Dications Revisited: Tuning Spin States by Confronted Arenes

Diradical dications of two kinds of alternate-meta-para-linked tetraazacyclophanes in which p-phenylene (1) and 9,10-anthracenylene (2a) moieties are embedded in their macrocyclic backbones were successfully isolated as air-stable salts. The structures of 12+ and 2a2+ were elucidated by X-ray analysis, and significantly different types of structural deformation led to different spin density distributions due to the steric demand of the confronted arene moieties. The singlet-triplet energy gaps were determined to be +0.3 kcal mol-1 (+151 K) and -1.0 kcal mol-1 (-503 K) by SQUID measurements, indicating the triplet ground state for 12+ and the singlet ground state for 2a2+.

Synthesis and Characterization of 6,13-Diamino-Substituted Pentacenes

A series of 6,13-diamino-substituted pentacenes 1u2009a-d has been prepared and characterized as a new class of pentacene derivatives with strong donor ability and enhanced solubility in common organic solvents. The spectroelectrochemical and DFT studies revealed that the two-electron oxidation process was accompanied by the substantial structural change into a butterfly-like conformation of the pentacene moiety. More importantly, the extent of deformation from the planar pentacene moiety in the dications of 6,13-diaminopentacene is tunable by varying the N-substituents.

9,10-Diaminoanthracenes Revisited: The Influence of N-Substituents on Their Electronic States

The electronic and molecular structures of 9,10-diamino-substituted anthracenes with different N-substituents have been re-examined. In particular, different N-substituents influence both the electronic and molecular structures of the oxidized species of 9,10-diaminoanthracenes. The anthrylene moiety of 9,10-bis(N,N-di(p-anisyl)amino)anthracene retains its planarity during the course of two successive one-electron oxidations, whereas 9,10-bis(N,N-dimethylamino)anthracene and 9,10-bis(N-p-anisyl-N-methylamino)anthracene undergo a substantial structural change to a butterfly-like structure through a two-electron oxidation process. The structural changes observed for the oxidized states are ascribed to significant differences in the frontier molecular orbitals of the above-mentioned three kinds of 9,10-diaminoanthracenes due to different extents of mixing between the amine-localized and anthrylene-localized orbitals.

A Triphenylamine with Two Phenoxy Radicals Having Unusual Bonding Patterns and a Closed‐Shell Electronic State

Reported herein is the structure and the electronic properties of a novel triphenylamine derivative having two phenoxy radicals appended to the amino nitrogen atom. X-ray single crystal analysis and the magnetic resonance measurements demonstrates the unexpected closed-shell electronic structure, even at room temperature, of the molecule and two unusual C-N bonds with multiple-bond character. The theoretical calculations support the experimentally determined molecular geometry with the closed-shell electronic structure, and predicted a small HOMO-LUMO gap originating from the nonbonding character of the HOMO. The optical and electrochemical measurements show that the molecule has a remarkably small HOMO-LUMO gap compared with its triphenylamine precursor.

Diazadibora[1.1.1.1]m,p,m,p‐cyclophanes: Ambipolar Conjugated Macrocycles with Different B–π–N Embedded Patterns

Are different B(boron)-π-N(nitrogen) embedded patterns to bring about significant different (opto)electronic properties for the same macrocyclic molecular backbone? A series of B-π-N-embedded alternate-meta-para-linked cyclophanes 1-3 have been prepared and characterized as a new class of ambipolar π-conjugated B-π-N macrocycles. The answer to the opening question is yes. These macrocycles revealed the intramolecular charge transfer in the oxidized states and the intriguing photophysical proprerties in accordance with the embedded patterns, suggesting the electronic structures are tunable by introducing multiple B-π-N moieties.

Modulation of Open-shell Characters of Amine-inserted Diphenoquinones via Structural Modification

In this study, a series of triphenylamine derivatives with two 2,6-diphenylphenoxy radicals (2u2009a-d), which could be regarded as amine-inserted diphenoquinones have been synthesized and investigated their structures and electronic properties. The structures of 2u2009a-d were confirmed by single-crystal X-ray analysis, showing the characteristic bond length alternation patterns for closed-shell quinoids. The solutions of 2u2009a-d exhibited clear ESR signals even at room temperature, indicating their thermally accessible diradical states. The NMR and ESR measurements showed that the diradical character of 2u2009a-d were increased in the order of 2u2009a<2u2009b<2u2009c<2u2009d, well-reproduced by theoretical calculations. The results of this work strongly suggest that the diradical character of this class of compounds could be tuned by changing the substituent on the central nitrogen atom.