This paper describes the design process for a digital instructional sequence on introductory quantum physics for upper secondary education. Based on a collaboration between teachers and physics education researchers, this sequence incorporates relevant theoretical foundations from the field of science teaching to promote meaningful and conceptual learning of quantum physics. The sequence is composed of units, which are being developed using the Go-Lab ecosystem (www.golabz.eu), a free online platform for teachers to create digital inquiry-based lessons. So far, the sequence covers the photoelectric effect, wave-particle duality, and tunnelling phenomena. This paper focuses on the sequence's first unit, addressing the photoelectric effect. The unit is used in this paper to exemplify the incorporation of the sequence's theoretical foundations: digital inquiry-based learning with simulations, collaborative learning, and conceptual change. The unit was pilot-tested with 114 students in four Dutch high schools. Answers to multiple-choice and open-ended questions were collected through the Go-Lab platform. Analyses showed the unit's potential to promote correct reasoning about the role of the intensity and frequency variables and revealed students' difficulties in grasping light's particle nature at the end of the lesson. These preliminary results are used to draw conclusions about how to improve this unit and inform the design of new instructional sequences.