Double Heterohelicenes Composed of Benzo[b]- and Dibenzo[b,i]phenoxazine: A Comprehensive Comparison of Their Electronic and Chiroptical Properties

Abstract

Heterohelicenes are potential materials in molecular electronics and optics because of their inherent chirality and various electronic properties originating from the introduced heteroatoms. In this work, we comprehensively investigated two kinds of double NO-hetero[5]helicenes composed of 12H-benzo[b]phenoxazine (BPO) and 13H-dibenzo[b,i]phenoxazine (DBPO). These helicenes exhibit good electron donor property reflecting the electron-rich character of their monomers and were demonstrated to work as p-type semiconductors. The enantiomers of these helicenes show the largest class of dissymmetry factors for circularly polarized luminescence (CPL) (|gCPL| > 10−2) among the previously reported helicenes. Interestingly, the signs of CPL are opposite between BPO- and DBPO-double helicenes of the same helicity. The origin of the large gCPL values and the inversion of the CPL signs was addressed by analysis of the transition electronic dipole moments (TEDM) and transition magnetic dipole moments (TMDM) based on the TD-DFT calculations.

A double heterohelicene composed of two benzo[b]phenothiazine exhibiting intense room-temperature circularly polarized phosphorescence

“…Consequently, 2 is highly asymmetric for the C 2 axis; the upper face is a convex side with the two benzene rings projecting upward, and the other face is an almost planar concave side. The torsion angle around the helicene moieties of 2 (60.7°) was much larger than that of 1 (48.3°), 7 indicating that the replacement of oxygen with sulfur atoms increased the torsion angle. The sum of the angles around the nitrogen atoms of 2 decreased to 350.6° compared to that of 1 (avg.…”

“…S25, ESI †). 7 Over the last few years, some organic molecules exhibiting long-lived CPP at room temperature have been reported. 18,[31][32][33][34][35][36][37][38] However, small molecules that emit long-lived CPP from a single-molecule state are still rare.…”

“…[9][10][11][12][13][14][15][16] We have recently succeeded in synthesizing a double N,O-hetero [5]helicene 1 (Fig. 1) composed of two benzo[b]phenoxazines (BPO), 7 and we comprehensively compared 1 and a double N,O-hetero [5]helicene composed of dibenzo [b,i]phenoxazines 5 to clarify how the presence or absence of additional benzo moieties affects their structures and properties. In the work, we found an unexpected result that the additional benzo moieties invert the CPL signs of the double helicenes of the same helicity.…”

“…In 2015, we established a simple method for the synthesis of double heterohelicenes by tandem oxidative coupling of heteroacenes with an NH group. [5][6][7][8] Heterohelicenes have attracted recent interest as potential materials with unique optical and electronic properties derived from chirality, such as chiroptical properties represented by circular dichroism (CD) and circularly polarized luminescence (CPL). [9][10][11][12][13][14][15][16] We have recently succeeded in synthesizing a double N,O-hetero [5]helicene 1 (Fig.…”

C3-Chiral truxenes showing high circularly polarized fluorescence and phosphorescence properties based on symmetry-forbidden transition

“…Organic molecules that show a large dissymmetric factor (gabs and glum) of circular dichroism (CD) and circularly polarized luminescence (CPL) have recently been extensively developed for use in a wide range of applications such as 3D displays, optical sensors, optical information storage, and encryption [1][2][3][4][5][6][7][8] . To date, several strategies have been proposed to achieve high CPL properties based on molecular symmetry, and the fine tuning of transition electric dipole moments (TEDMs; µ) and magnetic dipole moments (TMDMs; m) of structurally elaborate chiral biaryls, 9-13 macrocyclic molecules, 5,14-16 and helicenes [17][18][19][20][21][22][23][24] . The glum value is defined as the difference in emission intensity between left-handed (IL) and right-handed (IR) polarized light divided by the average light intensity where θ is the angle between μ and m [1][2][3][4][5][6][7][8] .…”