Kosar Naveen, Kanwal Saba, Hamid Malai Haniti S A, Ayub Khurshid, Gilani Mazhar Amjad, Imran Muhammad, Arshad Muhammad, Alkhalifah Mohammed A, Sheikh Nadeem S, Mahmood Tariq
Department of Chemistry, University of Management and Technology (UMT), C-11, Johar Town, Lahore 54770, Pakistan.
Department of Chemistry, COMSATS University Islamabad, Abbottabad Campus, Abbottabad 22060, Pakistan.
Molecules. 2023 Aug 28;28(17):6283. doi: 10.3390/molecules28176283.
Switchable nonlinear optical (NLO) materials have widespread applications in electronics and optoelectronics. Thermo-switches generate many times higher NLO responses as compared to photo-switches. Herein, we have investigated the geometric, electronic, and nonlinear optical properties of spiropyranes thermochromes via DFT methods. The stabilities of close and open isomers of selected spiropyranes are investigated through relative energies. Electronic properties are studied through frontier molecular orbitals (FMOs) analysis. The lower HOMO-LUMO energy gap and lower excitation energy are observed for open isomers of spiropyranes, which imparts the large first hyperpolarizability value. The delocalization of π-electrons, asymmetric distribution and elongated conjugation system are dominant factors for high hyperpolarizability values of open isomers. For deep understanding, we also analyzed the frequency-dependent hyperpolarizability and refractive index of considered thermochromes. The NLO response increased significantly with increasing frequency. Among all those compounds, the highest refractive index value is observed for the open isomer of the spiropyran (1.99 × 10 cm/W). Molecular absorption analysis confirmed the electronic excitation in the open isomers compared to closed isomers. The results show that reversible thermochromic compounds act as excellent NLO molecular switches and can be used to design advanced electronics.
可切换非线性光学（NLO）材料在电子学和光电子学领域有着广泛的应用。与光开关相比，热开关产生的NLO响应要高出许多倍。在此，我们通过密度泛函理论（DFT）方法研究了螺吡喃热致变色材料的几何、电子和非线性光学性质。通过相对能量研究了所选螺吡喃的闭合和开放异构体的稳定性。通过前线分子轨道（FMO）分析研究了电子性质。对于螺吡喃的开放异构体，观察到较低的最高占据分子轨道（HOMO）-最低未占据分子轨道（LUMO）能隙和较低的激发能，这赋予了较大的第一超极化率值。π电子的离域、不对称分布和延长的共轭体系是开放异构体具有高超极化率值的主要因素。为了深入理解，我们还分析了所考虑的热致变色材料的频率依赖性超极化率和折射率。随着频率增加，NLO响应显著增加。在所有这些化合物中，螺吡喃的开放异构体观察到最高的折射率值（1.99×10 cm/W）。分子吸收分析证实了与闭合异构体相比，开放异构体中的电子激发。结果表明，可逆热致变色化合物可作为优异的NLO分子开关，并可用于设计先进的电子产品。
