Thia[n]helicenes with long persistent phosphorescence.

Area of Science:

• Organic Chemistry
• Materials Science
• Photophysics

Background:

• Helicenes with persistent luminescence are underexplored despite efficient intersystem crossing (ISC).
• Dithieno[2,3-b:3',2'-d]thiophene (DTT) and annulated benzene fragments offer a promising scaffold for novel organic materials.

Purpose of the Study:

• To design and synthesize novel ortho-fused aromatic compounds (TB[n]H) for persistent luminescence.
• To investigate the photophysical properties, particularly phosphorescence and circularly polarized luminescence (CPP), of these new thiahelicenes.

Main Methods:

• Synthesis of a series of thiahelicenes (TB[n]H, n=3-8) by combining DTT with annulated benzene fragments.
• Characterization of phosphorescence lifetimes (τp) at 77 K.
• Measurement of circularly polarized phosphorescence (CPP) responses and luminescence dissymmetry factors (g_lum).

Main Results:

• Thiahelicenes (n=5-8) displayed intense phosphorescence with millisecond-range lifetimes at 77 K.
• Odd-numbered helicenes exhibited longer phosphorescence lifetimes than even-numbered ones, with TB[7]H showing the longest at 628 ms.
• TB[7]H demonstrated significant CPP responses with g_lum values of 0.015 and -0.014.

Conclusions:

• The observed differences in phosphorescence lifetimes are attributed to favorable ISC channels and stronger spin-orbital coupling (SOC) in odd-numbered helicenes.
• Thiahelicenes represent a promising class of organic materials for applications in phosphorescent and CPP technologies.
• The design strategy provides a pathway for developing new organic optoelectronic materials with tailored photophysical properties.