Donor–Acceptor Type Pendant Conjugated Molecules Based on a Triazine Center with Depressed Intramolecular Charge Transfer Characteristics as Gain Media for Organic Semiconductor Lasers

Abstract

A set of fluorene‐capped pendant conjugated molecules (T‐m and T‐p), which consist of a triazine center with three carbazole substituents as the donor–acceptor (D‐A) type pendant structure, were designed, synthesized, and investigated as gain media for organic semiconductor lasers (OSLs). In particular, varying the capping positions of the fluorene units on the pendant core structures results in significantly different intramolecular charge transfer (ICT) properties, where T‐m manifested depressed ICT characteristic and high fluorescence quantum yield. The lowest amplified spontaneous emission (ASE) threshold in neat films was recorded as 1.9 μJ cm−2 for T‐m and 83.8 μJ cm−2 for T‐p, which indicated that the depressed ICT characteristics in the case of T‐m help to enhance the ASE properties. Remarkably, the ASE threshold remained almost unchanged and the ASE spectra showed very small shifts (within 1 nm) for T‐m with film samples annealed up to 180 °C in open air. In contrast, its linear counterpart 2FEtCz‐m showed a clearly increased ASE threshold upon annealing above 100 °C. The results suggest that the selective construction of conjugated pendant molecules with depressed ICT characteristics is beneficial for finely modulating the optical and electrical properties as well as improving the thermostability and photostability, which manifests the great potential as a robust gain media for OSLs.

Molecular doped organic semiconductor crystals for optoelectronic device applications

“…[55][56][57] However, the design and synthesis of efficient organic laser materials are still facing great challenges, even with the great efforts that have been made in this field. 58,59 Molecular doped organic semiconductor materials have attracted increasing research interest recently due to their tunable ASE property and emission color. 60,61 In 2019, Zhao and co-workers prepared doped organic crystals using C60 as host and cyano-substituted oligo-(α-phenylenevinylene)-1,4-bis(Rcyano-4-diphenylaminostyryl)-2,5-diphenylbenzene (OPV) as a guest, 42 as shown in Fig.…”

Gain Bandwidth Engineering in Polymer Blends for Full‐Color‐Tunable Lasers

“…The amplification characteristics of all BEHP‐PPV:MEH‐PPV blended samples are summarized in Table S3, Supporting Information. As a point of comparison, the measured ASE thresholds obtained here are among the lowest values reported in dendritic starbursts, [ 42–45 ] polymers, [ 46,47 ] and guest–host gain systems under nanosecond pulse excitation. [ 36,37,48–50 ] Intriguingly, the peaks of green amplification in the blended polymers do not show any shift with respect to the blending ratio (Figure 2e).…”

Pendant conjugated molecules based on a heterogeneous core structure with enhanced morphological and emissive properties for organic semiconductor lasing

“…Besides, the smaller dihedral angels in C2 may also induce relatively stronger ICT effects relative to C1, thus resulting in inferior PLQYs caused by the small oscillator strength, which is consistent with our previous studies. 22,29 As compared with the analogue T-m based on a homogeneous pendant core structure (PLQY = 0.58), 29 higher PLQYs have been achieved for C1 and C2 based on a heterogeneous core structure. The results indicate that integration of a heterogeneous core structure endowed the molecules with enhanced PLQYs, mainly arising from depressed intermolecular aggregation induced by the non-planar architectures of the DPA-substituted triazine core structure (Fig.…”

“…While the films of 2FCz and 4FCz exhibited a similar surface with a higher RMS roughness (0.3 nm). Compared with the analogue T-m based on a homogeneous core structure, 29 the resulting pendant molecules C1 and C2 based on the heterogeneous core structures exhibited enhanced surface morphology with a smaller RMS, which may originate from the depressed intermolecular stacking induced by the incorporation of DPA substituents (Fig. S7-S9, ESI †).…”