Enhanced Photothermal Property of Dithienoindacenodithiophene Molecules by [2 + 2] Cycloaddition–Retroelectrocyclization Reaction for Efficient Solar Steam Generation

Abstract

The development of efficient photothermal materials for solar steam generation (SSG) garners significant interest as a solution to the global clean water scarcity crisis. Photothermal properties of organic molecules can be fine-tuned by molecular design. Despite this fact, the use of organic small-molecular photothermal materials in SSG applications is seldom explored due to their limited optical absorption range for solar energy harvesting. In this research, 6,6,12,12-tetrakis(4-octylphenyl)dithieno[2,3-d:2′,3′-d′]-s-indaceno[1,2-b:5,6-b′]dithiophene (DTIDT) is focused upon as the potent conjugated core unit, and the [2 + 2] cycloaddition–retroelectrocyclization (CA-RE) reaction is applied to introduce additional intramolecular charge-transfer chromophores. DTIDT derivatives exhibit broad optical absorption, weak photoluminescence, and high nonradiative decay rates, which are useful for efficient photothermal conversion. In addition, the DTIDT derivatives are placed on the top surface of a filter paper, and the SSG devices are fabricated as a Janus membrane to enhance the solar-to-vapor efficiency. The DTIDT derivatives produced by the [2 + 2] CA-RE exhibit a maximum efficiency of 78.3% under simulated sunlight irradiation for 30 min. The result suggests that the CA-RE reaction is an effective method for synthesizing organic photothermal materials tailored for SSG applications.