Volatile Aromatics Trigger Vapochromic and Vapoluminescent Responses in Cleft-Shaped 1,4-Bis(imidazolyl)benzene: Role of Charge-Transfer Interactions in Vapor-Induced Host–Guest Complexes

Advancements
in vapochromic and vapoluminescent materials
have
garnered significant attention due to their potential applications
in chemical sensing, environmental monitoring, and industrial processes.
The increasing demand for efficient, lightweight, and easily synthesized
chemical sensors has underscored the importance of developing small-molecule-based
vapor-responsive materials to meet the needs of modern sensing technologies.
In this study, the organic compound 1,4-bis(4,5-bis(4-bromophenyl)-imidazolyl)benzene
(1) was investigated for its vapochromic and vapoluminescent
properties. The cleft-like structure of compound 1, coupled
with its ability to form hydrogen bonds and π-stacking interactions,
enables efficient trapping of aromatic vapors. 1H NMR,
TGA, and PXRD studies reveal the formation of stable host–guest
complexes (1·guests), along with phase transformations
in 1 upon vapor exposure. Notably, single crystals of
select host–guest complexes grown via slow evaporation exhibit
host–guest ratios and PXRD patterns identical with those of
their vapor-exposed counterparts. Distinct color and luminescence
changes validated by diffuse reflectance spectroscopy (DRS) and photoluminescence
are attributed to charge-transfer interactions of the host with guest
molecules. Computational studies indicate that aromatic guests with
lower LUMO values exhibit stronger interactions, leading to significant
luminescence quenching, as further confirmed by the reduction in the
fluorescence quantum yield. The sensitivity, selectivity, and charge-transfer
properties of compound 1 establish its potential as a
robust candidate for small molecule gas sensors.

气致变色（vapochromic）与气致发光（vapoluminescent）材料领域的研究进展，因其在化学传感、环境监测及工业生产流程中具备潜在应用价值，已受到广泛关注。当下市场对高效、轻量化且易于合成的化学传感器的需求日益增长，这凸显出开发基于小分子的气响应材料以适配现代传感技术需求的重要性。本研究针对有机化合物1,4-双(4,5-双(4-溴苯基)-咪唑基)苯（编号1）的气致变色与气致发光性能展开探究。该化合物具有裂隙状分子结构，同时可形成氢键与π堆积相互作用，使其能够高效捕获芳香类蒸气。通过氢核磁共振谱（¹H NMR）、热重分析（TGA）与粉末X射线衍射（PXRD）表征，研究团队证实了稳定主客体复合物（1·客体）的生成，同时观测到化合物1在蒸气暴露后发生晶相转变。值得注意的是，通过缓慢挥发法制备的部分主客体复合物单晶，其主客体配比与粉末X射线衍射图谱，与经蒸气暴露得到的样品完全一致。经漫反射光谱（DRS）与光致发光表征验证的显著颜色与发光变化，可归因于主客体分子间的电荷转移相互作用。计算模拟研究表明，最低未占据分子轨道（LUMO）能级更低的芳香类客体分子与主体的相互作用更强，进而引发显著的发光猝灭，这一结论通过荧光量子产率的降低得到了进一步验证。化合物1所具备的传感灵敏度、选择性与电荷转移特性，使其成为一款极具应用潜力的高性能小分子气体传感器候选材料。